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This IBM PC XT won't turn on, let's fix it
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- Опубликовано: 28 июл 2024
- On today's video, I have an IBM PC XT 5160 that isn't turning on. This is a super common issue with these machines, so let me show you how to find and fix the problem.
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--- Instructional videos
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Adrian, I’ve seen the fault detection technique you used in this video demonstrated on other channels but none of them broke it down step-by-step like you did so that novice electronics repair hobbyists like myself could understand how to do it ourselves. After watching your video, I feel that I can deploy this fault finding technique myself. Thanks for the excellent content. That’s why folks like myself subscribe and continue to find value in what you do. Keep up the good work and know that you are appreciated.
I had an XT clone growing up. You might think I'd have some nostalgia for it, but I really don't. It was so slow, especially compared to my friends' computers at the time. It had a monochrome monitor with a Hercules knock-off graphics card, no sound card, and later in its life, a pokey 2400 baud modem that was only ever used to connect to the library's card catalog. It also didn't boot off its hard drive half the time--usually the half that I had a school paper due. The day I landed my own PC, with a 386 processor, a Sound Blaster card, and a VGA monitor, and I never had to touch that old XT again, that was one of the happiest days of my life!
I have mixed feelings towards my first PC as well - a 5170 AT clone my parents bought in 1987. I did learn a lot about computers from using it but it was slow (6 MHz) and the power supply fan was super noisy. In around 1990 I upgraded it to a 386SX-16, which was speed demon in comparison, but still laughably slow compared to today's PCs. An expensive upgrade, and I was still using the old noisy 5170 power supply. I don't think many people truly understand just how expensive PC parts were back then!
I have more fond nostalgia for the early 1990s era of 386DX clones, when I began running OS/2 and learned to code in C. To me, this is when PCs started to become truly useful. We take it for granted now but having a 386 machine in 1992 doing proper multitasking, and where the OS pretty much un-crashable, was revolutionary.
It's interesting how '80s PCs have now become collectible and often fetch a lot of money. I suppose it's because a lot of them were recycled or more likely became landfill, so any good ones left are a bit rare, at least here in Australia.
I love that the one time you try to show off how to find a shorted cap the proper way, it makes itself immediately obvious by being burnt out. The *one* time you actually wouldn't have minded it being a little less obvious!
imagine what happens when you replace the hard disk with an ssd
I am a retired Avionics engineer... I used a 5160 up until 2012... It was connected to a test station designed to test Audio Control Panels which reside
in a Boeing 747 cockpit... Changed plenty of tantalums over the years.. Love your video's mate
We are house shopping, and ever since I started watching this channel, I get way more excited over houses with enough basement to make my own underground digital domain.
Thanks for the great video. I sold IBM PCs and XTs from 1984-1987. The XT was discontinued by IBM in April 1987 when the PS/2 was introduced. A manufacturing date of 1986 would be late in the life cycle of the XT. Based on the full height 5.25 inch drive, this system would have been early 1986 as by mid year 1986, the XT switched to half height drives, allowing two dives in one bay and one HDD in the other front bay. At the same time MLB was updated to support 640KB on the main board without some form of memory expansion card. I installed lots of XTs with AST 6 pack + cards to add 384KB, Parallel port, serial port(s), game port and clock. At the same time that the XTs with half height drives were release, IBM also released the PC XT 286, with a 6 MHz 80286 to replace the 6 MHz AT which was speed bumped to 8 MHz. Lots of nostalgia for me watching this video. Thanks again!
Thank you for this glimpse into the past.
It is super cool to hear about the industry from the reseller perspective.
It is amazing you still remember every detail of what happened. I don't even remember 5 years ago LOL!
I still have my first computer, and it still works: an IBM PC 5150 (type B) with CGA and an AST Six-pack Plus like you mentioned (it has a bad memory chip so I have to run it with a little less than 640k. I should fix that.) It has a half height Seagate 20MB hard drive and some ROM chips dated 1984 which I think were to make it support hard drives. We got it used for Christmas 1987. I need a proper monitor for it (I can use CGA’s composite out though), or whatever that RGB to HDMI thing is. I added a Sound Blaster in it at one point. Wish I had kept it in there too. It remained my only computer until 1993 and it was really getting obsolete.
I have an xt and monitor only I am trying to sell. I am mulling over whether or not to scrap it for gold or preserve it.
Dont forget the good old smell test, I have found more than a few dead caps that way
Here’s a trick I use to remove those 3-legged caps:
Use side cutters to cut through the cap body diagonally from the top toward the middle, to shear the left and right legs off. It leaves a chunk of cap on the middle pin. Add a little extra solder on the center pin, and what’s left of the cap may just fall out. Then tweez the side legs out with some fresh solder to help warm them up. Use a solder sucker to clear the holes and replace with a new cap.
This really makes it easier because IBM liked to bend the legs out. If you only have one leg at a time to deal with, you can tweez it out at an angle or bend the leg back straight again. That’s much harder to do with the cap intact.
00:14:10 You can grind the longer jaw down to meet the shorter side while the cutters lead their new hard knock life. (you can re-sharpen the cutting surface with a few file swipes too)
The 5v rail isn't so carefully protected. IBM's power supply happily smoked the speaker cable on mine when I brought it through to an external speaker.
I see "quickly" in the video title and I immediately think: "Since when does Adrian does anything quick???".
Then look at the length, and go: "Oh ok, not THAT quick..." feeling reassured ;)
A quick visual survey of components can save tons of time when troubleshooting.
Exactly, the first step to any troubleshooting is a VMI; Visual Mechanical Inspection.
Used a modern PS with a 386SX board the other day. It was happy to supply enough 12V to flame 4 tantalums. Workshop still stunk the next day.
A customer called about a 486 pc with smoke pouring out of it, they put it outside on the lawn and called for service. One of the tantalum caps shorted and ignited a ribbon cable while the fans provided additional oxygen, it burned a hole in the motherboard. Tantalum caps are dangerous do not run power through them unattended.
I thought you were suppose to use a paper clip.... I hope you have a go at that power supply. Thanks for the video.
This got a good chuckle from me :D
Forcing a tantalum capacitor to go 'open' is hard. Tantalum capacitors are made from a small block of sintered tantalum metal powder coated with an oxide of tantalum, then further coated with silver for making the contacts. When a tantalum capacitor shorts out, the metal bits 'weld' together, making a very low impedance (and high current) connection. The more the tantalum cap fails, the more it gets welded together, and thus the lower it gets in resistance. Forcing a tantalum capacitor to 'open' like a paper/aluminum electrolytic takes immense amounts of current - at least on the PC power supply scale - so it is unlikely for the tantalum cap to eventually become an open-circuit. Aluminum/paper electrolytics will eventually explode or separate at lower currents, turning them into an open circuit that is harder to find (sometimes you just find the capacitor legs sticking out of the PCB). RIFA caps are similar, they'll explode and open-circuit, with an accompanying bit of bang and smoke. Anyhow, I love the channel and content, keep up the great work you do. Cheers!
p.s.: Tantalums are used extensively in Tektronix gear, mainly because they filter a wide range of noise frequencies. If you have a failed *older* (pre-1990) Tek device, look to the tantalums. After the 90s, they started using a lot of smd al/paper electrolytics, which leak and ruin the PCB. In either case, re-cap before powering up old gear, just to be safe. Newer tantalums (or niobium alternatives) are much safer, in general, due to improvements in the manufacturing process. MLCC ceramics can also come close to replacing tantalums in lower-capacity situations.
Indeed! some equipment that I serviced decoupled a power rail through a small inductor that would fuse when a tantalum shorted. Some 'Genius' had 'recapped' a Vital Industries SqueezeZoom (It was a $250,000 video processor in the early '80s) with cheap electrolytics, replacing the much more expensive sealed tubular Tantalums, so we were replacing them with the right parts at a cost of several hundred dollars a month. So much for the previous owner having a real Broadcast Engineer. 😡
@jshowa o In theory, but not in practice.
ESR can easily be measured in circuit Even a cluster of paralleled electrolytics can be tested. If you can identify the OEM, the series and type you can find the specification on a datasheet.
Keep in mind that as ESR goes up, internal heating also increases due to its inability to pass AC. I've been locating and replacing bad capacitors for over 55 years.
@jshowa o I have datasheets with the ESR information on hundreds of different series of electrolytic capacitors. Buy Panasonic or another premium brand that does publish datasheets, not no name floor sweepings from a Chinese factory. I supported mission critical systems, i didn't want more problems from cheap parts without proper data or quality control.
If five identical parts are in parallel, you will see 1/5 the specified ESR. If it is out of spec, they all need replaced because the ones that are in the worst shape are putting additional AC current through the rest. If you find no name crap in a switching power supply, you can look at the average ESR for that type to get a fairly good idea of what to look for. I prefer a digital ESR meter since most of what I find as defective are high capacitance. I first used a Sencore LC53? unit 34 years ago, to get a TV station straightened out after a lightning strike and power outage took down a lot of equipment that was powered 24/7. Every computer terminal was dead because of marginal ESR
I have also worked on industrial electronics, both in the field and at the factory.
Some of my work went into space, for the ISS.
@jshowa o Hi, the short failure mode is due to the teensy-tiny distance (a few tens of microns) between the positive and negative elements of the tantalum capacitor. When the capacitor fails, it is usually due to a breakdown of the separation (dielectric) between + and - plates. Essentially, the + and - plates are being connected by a small, but significant, conductor. As the capacitor starts to heat up, more of the electrolyte (spacer) degrades and the connection becomes stronger, eventually resulting in some smoke and even fire. *ESR* is another parameter of a capacitor, unrelated to a short, which determines the electrical conductivity of the dielectric when presented by an electric field - tantalums usually have very good ESR (less than one Ohm) because the dielectric thickness is small and dielectric constant is high, resulting in low *AC* resistance. A major advantage to tantalum capacitors is that they have a low ESR at low frequencies *and* high frequencies, making them a 'best of both worlds' solution. An aluminum can electrolytic has good low-frequency (LF) ESR, but it gets bad at high frequency (HF), so those are often paired with ceramic capacitors that have better HF performance, but lower top-end capacitance (usually a few uF). So, since a small tantalum capacitor can be rated in the 10s or 100s of uF, it is a great all-around solution, just a little more costly. And if you don't care about HF performance, such as in an audio device, tantalums are not necessary, since aluminum electrolytics are perfectly fine. I hope that helps - cheers!
I've lost count how many tantalum caps i have replaced in the last 10 years or so. Any its only going to get more common as time goes by. Basically Tants were very fashionable in the 80's to early 90's and work for around 20-30 years or so (roughly). So yes, here we go. Quite common now for them to go into short mode. But unlike in this video with a visibly burnt cap, they are usually not visible. Thats where you need a decent meter to find the fault. Good video!.
You can take a somewhat educated guess by looking at which ones are over rated by the smallest margin (16V tantalums on 12V lines tend to go faster than 10V tantalums on 5V lines for example) and/or on high ripple lines. Those go first, while others might last 3 times as long.
Thanks. You just helped me to identify the problem I have. I acquired a 2nd hand PC that, when switched on, went PSST and smoke came out. Now I know where to look.
Take a second look at your Hercules graphics card! It's not just a "original Hercules branded monochrome graphics card", but it is the second generation: It's the "Hercules Plus" also known as "Hercules RamFont". It has a mode where the 64KB accessible memory space is divided into 16KB of text/attribute memory and 48KB of font memory, allowing up to 8000 character/attribute pairs to be in video memory (and it provides hardware-assisted scrolling), which are chosen from a character set of 3072 software-defined characters.
For the hardware nuts among us: Count the memory chips on the HGC+! There is 80KB of dynamic random access memory (10 chips of 16K * 4), although in no mode, the ISA bus is able to address more than 64KB. I reverse engineered the memory scheme on that card, and it turns out (unsurprisingly) the card primarily consists of four "banks" each being 16K * 8, all of them directly adressable from the ISA bus. In RAMFONT mode, the banks are split into one char/attribute bank and three font banks (the three font banks at the non-slot-end of the card), in graphcis mode, all four banks are just used as bitmap memory. The interesting catch is: The char/attribute bank is backed by a second 16K * 8 "shadow" bank that contains a mirror of the odd bytes (attribute bytes) at the corresponding even addresses (the addresses of the character bytes), or possibly it was the other way around (i.e. character bytes stored at odd addresses). This means this bank is 16K * 8 and 8K * 16 at the same time. For the ISA interface, that bank is 16K*8, no matter what mode the card is in. When scanning out text modes, the bank is read as 8K * 16, so the character and attribute are read at the same time. This doubles the memory bandwidth compared to the CGA card (which has a single 16K * 8 bank) using comparable memory chips, and thus avoids the "snow" issue.
BTW: on the original Hercules, there was a similar design, although the card just is built to support basic MDA capabilities in text mode, so there are no more than 2048 characters in video memory. The shadow bank on the original Hercules is a single 2K * 8 static RAM chip.
The late Hercules clone cards everyone and their dogs have probably use page-mode addressing to fetch the character code and attribute byte from a single 64K*8 banks. They do not have such a tricky memory layout as the original Hercules card, but more complicated logic chips instead.
That’s a pretty interesting memory layout! Were there many alternate fonts for latin, for typeface nerds, or was it only used for the original Hercules mission of providing non-latin characters?
@@kaitlyn__L While I do have a Hercules Plus somewhere, I didn't manage to obtain the original software. I wrote a small test program that switches to ramfont mode and copies the 8x8 CGA graphics font from the XT BIOS ino the Hercules Plus, which worked fine.
Apart from non-latin characters (maybe even kanjis?), a multitude of fonts is also interesting for WYSIWYG word processors that can display bold or italic characters in text mode, without falling back on color or intensity coding.
Hello sir, as I have seen more of your videos you sound more and more like my electronics teacher at Vocational School. This is a positive thing for me and I enjoy watching and learning about XT's, I am an ATX fan myself from 2007 - 2010 era. Thank you for making videos and sharing your knowledge with the world. I hope you have a pleasant day, and also everyone else have a pleasant day.
Great video as always Adrian.
Yes the common used name for the clock module was the SmartWatch that was also used in the Tandy 1000's as a optional upgrade.
Worked for a school system. Lost count of how many of these and similar XT AT cases Ive sent to the dumpster or later a recycler when they started getting picky about what went into the trash can! We literally couldnt give them away!!! Even us IT guys didnt want these boat anchors...........until now!!!!
11:30 - LOL, looks like a failed popcorn attempt :D
Another fantastic repair and diagnostic video. Your videos are quickly becoming a must-watch for me. Keep up the good work!
as a guy who often does component level repair on newer stuff(typically GFX cards and motherboards)(Mainly Gigabyte motherboards cause they all fail the same way between the 7-10 years worth of moderate use mark)
this channel is awesome to watch, gives me the old time repair nostalgia feels.
I had an XT, a 486 and a 233mhz machine, and tried to get the XT running on the internet via a TCP/IP stack over RS232 and Windows 98SE internet sharing, and got it working with a DOS IRC client and a text only dos browser of the time so my mother could continue chatting in IRC channels(the site she normally used, had a webpage overlay, that was just a hidden IRC client that I found what server it connected to.) while I used the main computer for something actually useful.
Sometimes, the easiest way to locate a shorted component is to source a current-limited voltage on the shorted rail. The shorted part(s) will get warm and is detectable via touch or IR temp.
I also use the "low ohms" function of my Fluke 289. It sources 100mA and is better than the regular ohms function at finding shorts.
I've used that method a lot. It's especially helpful when then the problem is an IC.
it gets better as the video progresses, as he focuses more on the task at hand, and less on using a radio broadcaster's modulated voice.
I remember having issues removing from an old GPU leaking through hole capacitors, fortunately there were some alternative pads for an SMD, so I just cut the old caps off and soldered some new caps onto these.
A nice one, Adrian. I wish you success when you attempt to fix the rest of the computer.
i haven't heard that harddrive sound in decades. brings back memories. i grew up calling the xt power switch the "BRS" interrupt...aka "big red switch" interrupt.
Great video. I hope you will doing more repair videos on this very computer!
I've had exactly the same issues on the same rail on the same genuine IBM motherboard. I ended up looking at the schematic to trace it down, as mine wasn't visually damaged. It was also a super easy fix....
Now I bought one of these XT class machines and before turning it on I measured for shorts on mother board power supply connector - everything was ok. Turn on lever up - power supply not working. I measured motherboard again and found that there is short on -12V so Your video will be helpful for me. Thank You.
All hail the 70's Towel! That PC looks in fairly good condition. I remeb er my first time seeing these at work they were so expensive!
Thumbs up for helping people. If anyone wants to actually do this, find the closest IC, bigger the better, and simply tack any new caps across the rail and ground pins. Don’t screw around soldering on vintage PCBs unless you are seriously experienced. Your going to wreck the board, typically by delaminating. And absolutely don’t use a USB soldering iron. They are useless for board level work.
Another great video-thank you!
I have an XT I need to ressurect, thanks for making this video, now I have a place to start.
Loved the video, my first ibm xt’s all had Hercules cards loved the hi res with orange and black mono display. Cga came as a shock because despite having 8 colours the resolution compared was terrible.
One of these were my very first PC type computers. I got all the pieces to put it together so I got a crash course in IBM XT computers. This video makes me miss mine. LOL
Super usefull video Adrian. Thanks..
Putting the board on a heating plate like a candle warmer can in most cases add enough heat to make soldering possible on the ground plane of those old 5150s. I chose a candle/coffee warmer because it won't be hot enough to damage anything but adds enough heat to the traces that the soldering iron can do the rest. It was a real pain where you sit before cheap mug warmers existed though.
Keep up the good work.. very interesting fault finding video. 👍
i use a hair dryer too heat the whole board up before, makes the desoldering easier for me
Some some low melt solder for areas that are hard to melt. Works wonders. You don't need the crazy heat.
Thanks for the tutorial!
always enjoy your videos !!!!! Thank you !!!!!!
Hey Adrian, I just saw an interesting video by Cathode Ray Dude (Headstart's PC With The Weird GUI "OS") who looked at an old PC clone and he did a nice quick history on graphic card standards. I'm sure you may know how they all fit in, but it was nice to get that perspective. The other interesting point he made is that the original IBM PC standard lasted almost a decade from 81 to early 90's (even with the XT and AT additions, which didn't supplant the original).
Watch out for those clippers snapping and putting an eye out! A big piece of one of the tips snapped when I was cutting through plastic and hit me square in between the eyes. It would've been a bad day if it hit me in the eye. I guess the fatigue finally built up enough in the very brittle / hardened metal.
0:01 Oh I seen this before on 8-bit guy. You just need a paperclip. Make sure it's super rare and collectable first.
Nice job! Cool shirt 👍
I have the 5160 which did work when i did get it (including some disks). Weeks later, when i did want do do something, it didn't. In the psu, a capacitor was shorting 12v. Now repaired, and the computer works again.
Fun video, thanks!
I believe the culprit for my XT was actually the same cap, though on an older board. The PCB being hard to solder on is legit. In my case, I think I just left the cap off since I read that it tends to be fine. And so far that's been the case. MinusZeroDegrees has a really good guide to pinpoint a bad cap as well since it's so common.
As the rail isn't used by the motherboard itself you should be fine without the onboard capacitor. Any cards which need the extra filtering probably have their own capacitors on the rail.
Groundplanes sucking away the heat I need for soldering is a problem that common, that I tend to call power planes "heat sinks for soldering joints". You don't necessarily need a high thermal mass iron, but you definitely need to put in a lot of power for some seconds into that joint to melt it. That heat can come from a high thermal mass, or you have a powerful heating element close to the tip that creates the heat just in time. Having the temperature sensor in the tip instead of the heating element also helps to prevent the tip to cool down when a high demand for heat exists. Professional JBC stations are known to be quite good at just-in-time heat delivery, but they also carry a quite "professional" price tag.
@@tw11tube I'm able to solder it with actually some cheap but nice Chinese soldering station I have. Before I had that I only had a RadioShack plug directly into the wall iron. Which combined with being so long and thus awkward to hold, was a very bad experience. Unfortunately one of the ISA slots bears the scars of this xD luckily it's not functionally damaged at all, just aesthetically.
@@tw11tube You don't need something that fancy. My old-school 140w soldering gun makes quick work of components on ground planes. The power is controlled by a finger trigger so if you let go when it melts you won't overheat the board. In this regard it should theoretically be safer than cranking the temperature on a thermostatic pencil iron.
New versions of the Weller soldering gun are available for much less than a JBC station.
@@eDoc2020 Those soldering guns are WAY too unreliable and hot. I've seen them overheat and destroy pads/traces so many times. They have so much power that by the time the solder melts the heat is just skyrocketing.
The ACTUAL trick to desoldering ground plane pins is to warm the area with a heat gun or ceramic hot plate at maybe 100-200 deg C for a couple mins. That heats up the entire ground plane so your iron has much less work to do. It results in a much better repair job and you're way less likely to destroy pads/traces.
When you break the point off your wire cutters, you can grind down the other side to match so at least they act like diagonal pliers. It won't make them good again, but it will make them somewhat more useful.
Thanks for another fun video Adrian! - Love the color of that mainboard (anything but green!). Also, does anyone know what the bodge-wires (Visible @ 12:05) on this mobo are for?
Your audio sounds great. What mic do you use?
I love your videos bro
Used to run my WWIV BBS on one of these with a USR 14.4. Snazzy.
What for a Big MFM Harddrive!! Your Videos are Great!!
Hello my friend! Nice to do something kind of 101 level instructional. What was the issue with the RGBTOHDMI? Just old settings getting in the way or an actual hardware issue?
Tantalum caps around 70s, 80s and even 90s are a common cause for failure, I normally replace all before I first try to power on anything.
Same here. They're cheap. Just replace them.
this unit reminds me of when i got into my first PC, just transferred to D.C. newly married, wanted PC went with USED< Newspaper Add listed units like this 200.00 with Monitor and Keyboard/mouse. this was around 1997 so many corporations were upgrading so getting read of old units any way they can made a cash cow for the Entrepeneur, so as "I don't know crap about PC" I bought one" that was the start of computer endeavor. wish i hung onto ti. was nice to work on.
you could've picked these for free in 90s.
should have stashed a lot.. a guy in university had some barn full of 80s and 90s stuff in '00s
If you have a hot air station, you can also use that along with a soldering iron to get the heat into the board.
My preferred method is to install an atx PSU (preferably with paper clips) and blow the thing right off the motherboard.
Yup, feels like real life. You fix one small issue, the tantalum, and then 10 other issues pop up. Well, it's going to be a great restoration series at least.
I consider myself a good tech, but Adrian is better than I am.
Nice fix.
I recently had an original IBM Seriell/Parallel card plugged into my 286 motherboard, and this card had a shorted tantalum. However, I wasn't so lucky and it simply burned through the thin +12V and -12V circuit lines on my motherboard in some positions on the bus. Luckily nothing else got damaged, but now I sadly have some patched conducting paths on my otherwise pristine 286 board :(
Scars of endurance! Just like sewn-up patches on a favourite piece of clothing, or indeed real scars on an actual person 😁
The ROM socket clock is interesting but too bad they didn’t leave external pins or terminals to install an external battery. How convenient that you have the cover off of an XT so that you can help VWestLife test the set of 8 bit ISA cards that he bought at the thrift store this week. 😆
And the mods to add battery terminals onto those chips are REALLY ugly! Albeit possible. But thankfully nowadays there’s Dallas Clock compatible hobbyist clones with a regular 2032 lithium slot :)
nice meter.. Dave would approve.
screeching switch mode psus can be caused by a bad base driver cap for the power switching transistor, assuming it uses a bipolar type not mosfet, this was an issue with many crt tv psus, especially in the 70s and 80s
The 106 on the capacitor is actually more than just some identifying number you have to look up--it's a code for its capacitance! It works the same as the resistor color code, with the first two digits multiplied by 10 to the power of the third digit, in picofarads. So this capacitor is 10×10⁶ pF, or 10,000,000 pF, or 10 μF. Voltage rating is usually not marked on capacitors this small, so generally just use your judgment on what an appropriate voltage rating is. On a -12 volt rail, I would say 20 or 25 volts is a good rating; 16 volts is a little too close to 12 for my comfort, but I tend to use wide margins where possible and 16 is probably fine.
It's usually fine to replace a tantalum with an aluminum electrolytic (I specify aluminum because tantalum caps are also electrolytic!), as long as you're replacing an *old* tantalum with a *modern* aluminum. The main advantage of tantalum caps historically has been their low ESR and small size, both characteristics that aluminum electrolytics have improved on since most of these computers were made. You can usually replace them with MLCCs or film capacitors too, but sometimes the low-but-not-super-low ESR of tantalum is necessary for circuit function (like stabilizing a low-dropout linear regulator), so make sure you aren't making the ESR *too* low.
I got my old dell dimension 2350 working again just by disconnecting power from a cd drive.
It's os is xp pro of course. Still browsing the web with it.
This video reminded me of something I've heard argued time and time again, that being, the argument both for and against "shotgun" cap replacement. I'm honestly of the opinion that just cause a cap hasn't shorted, opened, or leaked all over the board, doesn't mean it's still good. A lot of these "vintage" components have seen years, decades of use, they have gone through thermal cycles and undergone all the things that parts that have failed have also gone through... My opinion, is why risk it. If I have the device open already, I may as well replace any component that is suspect to fail. A cap that has not leaked or shorted, is one that could leak or short next month, or next year... then I have to open things again. Maybe the board gets damaged and I don't open the unit up again till the damage is already done... Not worth the risk, when parts are known for common failure modes. As far as arguing expense goes... Well, my argument is what's more costly, a handful of caps now, or hours of board troubleshooting and damage repair later, and potentially needing to replace whole boards, if the damage is not noticed in time before extensive damages occur?
My time and expense replacing all potentially unreliable components is worth my time later in having faith that the machine will continue to run, and not need more extensive work later.
I've lost count on how many of those computers I have tossed out back in the day. They were worth nothing in the 90s...
Nice faultfinding!
Fresh solder? Boards were wave soldered with a higher melting point solder than is used for rework.
Trying to use an ohmmeter to find shorted parts is not reliable, because of contact resistance. At my bench at Microdyne I used a HP651 test Oscillator and a 10:1 step down transformer to convert the 50 ohm output to 0.5 Ohms. (10*10/50=0.5)Then I used a Fluke 8920 True RMS voltmeter to follow the power rails or other traces with problems. A 0.1 volt P-P 1KHz signal wouldn't bias any semiconductors or cause any damage. Troubleshooting was simple. I would probe the ground at the four corners. The one that was the highest was the problem area. Then I would follow a trace. You would see the voltage drop, the further you were from where the signal was injected. Once the next spot had a lower drop, you had found the pad part because the short was at the last point with a significant drop.
I did this on new boards with problems coming out of our reflow oven. We had to keep rework to a minimum.
BTW, the power transformer that I used was from a damaged Commodore 1541 disk drive. You can use a scope in place of the fluke meter, but I had it and a Tektronix 2465B on my bench. With a schematic, I didn't have to look all over a board to find the dozens or 100+ connections to a power rail on VME/VXI cards.
That blown capacitor looks like a roasted corn kernel. 🌽😋
A couple weeks ago I picked up a pair of 5160s, a 5150 and a 5154 monitor. I haven’t gotten to checking them out yet, but I do know one of the 5160s doesn’t power on so this video is good timing.
dallas rtc chips are a maintenance nightmare, your best options being to carve into a sealed chip to solder onto internal traces... oh god why did they build it that way.
To make you buy a replacement when the old one went belly up.
Once you’ve dealt with a few boards ravaged by leaking NiMh or NiCd batteries, you’ll let a gasp of relief when you see a Dallas chip! Seriously, cutting into one and soldering two wires to it is so much easier than attempting to fix potentially dozens of bad traces or vias eaten away by battery corrosion.
In other words, the Dallas chip will never leak. It’s just a tiny coin cell (which is already unlikely to leak) potted in epoxy.
Saludos desde Mexico!!!
That burned capacitor looks like a burned popcorn kernel. 🤣🍿
A nice meter with 4wire resistance mode or a mOhm meter would help a lot.
Aaah the good ol Tantalum capacitors. We called them "the sweetcorn caps" because of their appearance. Hardy little buggers they are and hard to pop them. Must have been quite a high load to burn it out that bad. Crispy Scorched Sweetcorn, yummy!
I used to service them , the memory used to be comman as they used to creep out of the sockets. I belive the IBM psu also had a timed shutdown if the short persisted.
My XT had the build date on a cloth label attached to the PC speaker cable. Makes me wonder if there's one on this machine.
I started with an Atari 600 XL, but the IBM XT was my first "proper" computer!
You could build a dummy load to avoid having to risk valuable hardware. A couple of resistors will be enough.
yep, or car bulbs, although they have very low cold resistance so may male a psu overcurrent shut off ,, maybe bulb and resistor in series..?!
I think the hard drive was already cooked. I have a whole box full of dead drives with a few connected to a Molex splitter just for this purpose. They make great (and helpfully noisy) test loads.
please continue fixing it, please
Hello Adrian, idk why but RUclips unsubscribed me (I was just waiting for some of yours new vid, but nothing so I looked to your channel and…boom)
Fun fact - the little fabric tab attached to the speaker cable says when the machine was built. :)
Nice door stop.
Said it before, say it again; I find watching pepole do stuff in fast-motion, makes me laugh every time.
thenks you
I know there are kits to build an xt with new or new ish parts like you can for the pet or the apple 2?
That floppy drive sounds just dandy. Nothing wrong with it.
do you know anything about a hp multimedia 6100 desktop I looked and couldn't find any info about it
I'm surprised that the person you got the machine from didn't mention the foul stench that cap should have made when it burned up.
Can you investigate in that psu? Maybe it’s fixable.
Hi, had question on technique to find the bad rail. Did you have in continuity mode and then put neg probe on motherboard neg line and pos probe on 12v line? I just couldn't see because your hands were blocking and I know it is a tight space and I'm wanting to learn.
Yes, continuity mode and checking for shorted pins to ground.