Sencore VG91 repair part 2
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- Опубликовано: 12 сен 2024
- With schematic in hand I forged ahead and was greeting by success! Replace those power supply caps before it's too late!
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Congrats Bob! All you needed was the schematic and some voltages. WTG!
Wow Bob Great job but not surprised you really have amazing skills and really know what your doing. I cheat I watch and learn the ez way. Thanks for allowing me the great joy of learning from you and teaching me so much. Love this channel.
Congrats!! Glad to see it wasn't anything logic related! May be worth checking the tva92 for corrosion woes too...
the 78xx series tops out at 24V, so that could be one reason. you can shift a fixed regulator's output up though by putting diodes and/or zeners in its ground pin to raise it up by the drop of the zener(s)/diode(s). The 317 is pretty nice though since it only needs two resistors to set its output and it can handle higher voltages than the 78xx series can. it is also rather precise when when using 1% resistors
I should have checked this video was out before commenting on the previous video. Glad you got a schematic and was able to resolve the problem.
Bob- You are very lucky to have found the problem. Last piece of Sencore equipment I spent days on it, and an EE did too with no luck. Sencore wanted (at that time) $250.00 just to look at it, plus shipping. At that time I vowed not to ever buy their equipment new again.
Congratulations on the successful repair.
Wow. I never knew there was a backlight in the display! I'm glad to see you got it fixed.
The protection in those linear regulators seems like it could have been better thought out. I believe that instead of shutting completely down, that it just "folds back" the output until the temperature drops to a safe level. Then it starts all over again, until something breaks. It seems that a lot of designers like to push those regulators right up to their very limits, and I'm sure that doesn't help either.
I will definitely be inspecting my own VG91. (Another thing that probably doesn't help -- I'd guess these things all have tons of hours on them, having just been left on constantly when not in use.) It's disappointing that Sencore chose to say "you probably can't fix this, just send it in" as opposed to providing complete service info. That's all well and good until the company ceases to exist or won't support a product any longer! It's almost like they went out of their way to make it "service hostile", with no basic markings on the boards for voltages and such.
I'd guess that Sencore keeps complete modules on their shelves, perhaps ones that have been refurbished, so fixing is fairly easy if expensive.
Congratulations!! Hope someone will Please be kind enough to post some of the service information where some of us VG91 owners can see it. I have one of these which was damaged in shipping a few years ago and noticed the same "grunge" on the PSB you noticed and wondered about the caps leaking. That grungy area also lines up with the vents on the top so it also tends to have dust and debris there. Will get those caps replaced when I can. Thanks again for this great video!
Back in the saddle!
Really nice repair Bob! I swear you can fix pretty much anything!
Nice work, glad to see the repair turned out ok and the VG91 is up and running plus a display backlight. It should go brighter so the EL lamp is probably getting weak but at least there is some glow now.
Glad it came together and was a pretty straightforward fix. Regarding why Sencore use the Adjustable 317/337 instead of fixed is they could supply some non-standard output voltages if required by only changing one resistor.
Sure, but aside from 30, the rest are standard. They could have reduced part count and complexity.
0:36 Inspecting equipment using the old troublesome series of Nichicon caps for leakage is a good tip, but if those caps are mounted like these one; sitting right on top the board with no space inbetween, the leaking electrolyte is trapped underneath and when you see it oozing out the damage is already done. I had some of them literally fall off the board at the slightest touch because the leads had been eaten away and only the gunk was keeping the caps in place.
This is why I came to mount even the bigger electrolytic caps with a 1-2mm gap to the board.- Unless it is an application where constant vibration may stress the solder joints or vias, or height is an issue, there is IMHO no downside to it.
And some of you may recall even how in the 80s a lot of radial electrolytic caps even up to several 100uF on PCBs actually had S- or U-shaped bends in the leads near the case, that would prevent them from dropping in flush with the board on the assembly line. On those designs leaking electrolyte could easily be identified by green or white crusties on the legs where it could at least partially dry up - and emit the fishy smell we all know.
Good advice. I left about 2mm under the new caps.
I guess one could turn the caps completely upside down, extending the leads as necessary and hot gluing the body end onto the board. But why is the vent on the bottom, not the top, anyhow?
Good work, Bob. Very nice troubleshooting.
I am half way through, and I wondered if the LM317 has current limiting, and yes it does. Now watching the rest to see if the problem is something loading down the regulator output.
Happy for you to see you got it fixed Bob
Bob,
So happy for you! Now if I can do the same for mine. I think this was a good lesson for all of us with broken VG91’s! Any chance you could share the schematics for us?
I only have the power supply schematic. I posted it in the community tab of my RUclips channel.
Glad you were able to get it going!
Well done, Bob!! 👍
Awesome work Bob!
Sweet! Congratz! :)
We know a guy in LA with a very cool document scanner; would be nice if the folks with the full manual could loan it...
There is only a schematic - no service manual was ever produced.
@@bandersentv oops. Thought you mentioned someone had the whole thing but was too big to scan and send. We can dream...
HOO-RAY
Lm 317 does have more amperage output if I remember correctly. Also possable they wanted future upgrade possabilities as the LM317 has different pinout than fixed 7805 15 ect.
No they are both 1.5A
I may have posted in part 1. I would like a recommendation of a prom programmer to read out all my Sencore proms. I may have some, but don't want to go pulling the chips out until I am ready.
TL-866 style programmers are widely cloned by seemingly everyone in China (so extremely low priced) and tend to work pretty well.
How about a link for the schematic and BOM. Thanks and keep up the great work.
It is not online. I was emailed just the power supply schematic.
Bob, what is the best way to send you a photo of a radio.
Email bandersentv@gmail.com
What is it!!!
I will never use Nichicon caps this is a common problem with them ruining the PC board.
Had them do this in a computer a pain to fix the board near the processor.
Only use good caps made in US or Europe more money but worth this not happening.
It wasn't a Nichicon-specific problem, every major manufacturer of low ESR caps used similar dielectrics that have all aged terribly. Have found low ESR caps from Chemi-Con, Rubycon, Elna, Panasonic, Sanyo, Philips, etc leaking. I don't really think it was quality control issues, just the known dielectrics to get low ESR 30 years ago were primitive and as we're learning now volatile and not long lasting.
What caps are made in the US?
@@bandersentv..."Sprague"...(?)
@@daleburrell6273 they went out of business years ago. Vishay owns the brand name now and they only make a few types. The old orange drop and atom caps that cost a premium and I'm not sure where they are made. The old Sprague factory closed in the 90s.
I use Kemet. They seem OK so far.