Are bad caps a thing? ZX Spectrum 48k rubber key repair!
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- Опубликовано: 2 авг 2024
- Another quick(ish) vintage computer repair.
This poorly Sinclair ZX Spectrum has a corrupted display. Bad RAM? CPU?
Capacitors?!?! Maybe!
Initial checks video
• ZX Spectrum (48K & 16K...
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00:00 Introduction
00:39 We're going in!
01:47 Mostek CPU
02:20 Checking resistance
02:35 Removing the Voltage Regulator and Transistors TR4 and TR5
03:33 Powering on
03:53 Composite mod
04:53 Powering on (Again)
05:31 Checking Voltages (and a slip)
06:38 Replacing the Capacitors
06:50 A Clumsy Mistake
08:54 Testing
09:13 More Recapping
09:37 Testing and Success!
10:00 Finish the Recap
12:12 Replace TR1 and TR2 Transistors
12:56 Screen Test
13:15 Put it Back Together
13:37 Testing with CRT and loading Jetpac
14:08 Check Scraped Trace
15:19 Goodbye!
#zxspectrum #computerrepair #sinclairzxspectrum 
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Thanks for posting these speccy repairs as I'm trying to have mine more functional.
Thanks for watching! Good luck with your repairs 😁
Today I found out that the NES games "Solar Jetman"(which I loved as a kid) is actually the 3rd in the series, where Jetpac and Lunar Jetman where the number 1 and 2 and both ZX spectrum games.
I will have to give that a try!
Another disadvantage of sockets is that they add extra parasitic effects on the signals, which may become a problem when running the system at 4 GHz for higher fps...
How I laughed ... "That is odd ... so is your face!" Another cracking video showing that even the best of the best are always learning and refining their techniques. Everyone's human and most of us have odd faces.
Never stop learning!
Never stop having an odd face!
no need to disconnect the 2 modulator leads to composite mod it, you can even leave the resistor connected to get 'simultaneous' rf and composite out .. also reducing the emitter resistor of the modulator drive transistor by half can improve negative going parts of the signal as for recapping, i dont generally hold with 'blanket' recapping, its mostly unnecessary, they last better and longer than many think, dried up reset cap can cause a 'no start' issue, dried up c46 can result in fried lower ram, so i'd replace those first , maybe fit a non electrolytic instead, so should last 'forever'..
Love these quick fix videos. Maybe I've been lucky but I've tried the earlier Speccy's with LCD and plasma TVs and the image was better than a portable CRT.
Thanks Captain! I think the one I'm using as a test screen is just not very good. My old one was great, smaller and better picture. But that one developed a fault where the earth shielding on it was at 100v 😱
Nice too see, keep up good work!! , and thanx for making me smile 🙂
Hey! You made me smile too! 😁
Wise man is Future Lee
He'll read your tealeaves if you cross his palm with a broken 8bit computer
Nice video and interesting to see a fault like that caused by dodgy caps. Its actually making me wonder about a system I'm trying to repair at present with odd behaviour, its not a spectrum but its got plenty of old caps on there...
Thanks Glenn 😁
Hope your fault is simple but interesting!
Entertaining and educational as always!
Thank you Chad. I always look forward to your super positive comments :D
I've pulled some very bad caps out of speccys. The last one had a 22uf measure as 66uf and that computer was working!
I did measure some of these and they were similarly terrible
Nothing as bad as that but recently had some measuring 40+!
Lovely as always! Interesting stuff!
Thank you Snorkers!
Subscribed!
Thank you!
My guess is C27 was the bugger here. This capacitor is part of the reset circuit which holds the RESET line low on power up as it charges. If it charges up too fast (due to decreased capacitance) or doesnt charge up at all, the system doesnt get reset properly.
I think you described exactly what was happening here. Other than that things seemed functional. The dcdc was working as expected, just wasn't starting up every time.
Great video, and very valuable for new and old enthusiasts to be mindful errors can be made! Great content as ever!
Thank you Jonathan 😁
Love these videos thank you!
I love that you love these videos! Thank you 😃
I hope that you re-fitted the heatsink when you opened it again to check the trace.
Very well spotted! I did indeed fit that. 😂
cracking vid matey :D
Cheers Sparks! I really enjoyed this one. I've got the other one from you in the pile for when I want to scratch my speccy itch 😋
Great video. I have an old 48k wonder under the bed that last time I tested it (about 10 years ago!) It had very wobbly video out so I think it's due a recap, so got the ZXrenew kit that I need to install and do the comp mod, so your video is a nice reminder to do that! Nice tip on heating a blob to extract from the top.
Thank you Chris! 😁 Good luck with your Spectrum. Hopefully the cat didn't find it under the bed and use it for keeping hairballs in.
Another great video. Well done.
Thank you Curtis 😁
Another one coming tomorrow. I'm on a roll!
@@MoreFunMakingIt Nice.
@@MoreFunMakingIt I’m also glad that Jan Beta resent your message on mastodon so I could find you there.
Same! I'm sure eventually we'll work out how the new platform works and find everyone we need to
Ouchy regarding the thumb. I hope its okay!
It was so quick it didn't even leave a mark! I'm invincible!
Muy bueno👍
Thank you! 😁
By default I generically replace the caps on all machines these days. Especially where heat has is involved...
I'm far too lazy and short of time to recap everything! 😂
Just so you know, shorting the output of a 7805 to ground shouldnt kill it. They have internal short circuit protection, so they should just shut down. The voltage converter circuit may not like it though as it uses the 5V line as a reference voltage
Always good to know!
i cut the legs before desoldering on pin at a time
That's absolutely the safest way.
You must also jam in a TRS-1 2450.
If it was my own I certainly would! Love a Traco 😁
Can you do a video on reducing jail bars on a 48k Spectrum please ? I repaired one once and no matter what I did to it (all new caps, composite mod) it had terrible jail bars.
If I come across a machine with that problem then sure!
Did you miss the center screw to fix the pcb to the lower case when mounting it back? ^-^
That's very well spotted. It was actually missing when I opened it up!
@@MoreFunMakingIt Nice repair video as usual. It reminds me that I still need to do a recap on one of my Speccy 48k 🙂
Isn't it easier to cut off these capacitors and then desolder their pins?
Sometimes!
So it's not always the RAM ?
No. It's always the ram.
Always!
@@MoreFunMakingIt Thank you for the spectrum measuring video link I will bookmark that one, perhaps you should bring it up to date with less stiff upper lip ness ? also add waveforms from the scope
@@leesmithsworkshop that would mean pretending I know what I'm talking about 😂
Why is "JETPAC" without a "K"?
Because it's cool! Probably.
Are each of these quick repairs getting longer? are you just slowly weaning us to watch a three hour repair?
You've seen right through my plan! Now go and watch my 13 episode pinball build!