Sinclair ZX Spectrum+ repair attempt - Several faults - Part 1

This ZX Spectrum+ did not power on, and after fixing that, there where more faults!
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Repair attempt on an old Sinclair machine. It did not go well in this first part.
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[@miked4377]

i hope to see you soon tommy.. you have a great channel for a retro collecter and game player...like me

[@Arcticretro]

I hope so too! Thx!

[@Xoferif]

13:02 It's very important to measure all three voltage supplies to the lower RAM chips as soon as the machine is powered up. It's very common for a faulty 4116 chip to overload the voltage generation circuitry, which then fails, and in turn damages more 4116 chips.

[@pe1dnn]

Yes, the 4116 is actually a 12 V chip and 5V is just for the data- and address bus interfaces and -5V is just a bias voltage. And they no not like to have the bus buffers powered but not the whole chip.

[@JonnyFix]

@@pe1dnn He only measured 8.5 on the 5v reg input, could his power supply be too low or would the 12 in be stepped down before the reg?

[@Xoferif]

@@JonnyFix The voltage generator circuitry takes the output of the 5V regulator and generates 12V and -5V from it. 8.5V going into the 5V regulator sounds about right.

[@Arcticretro]

Yes. I actually did. Not everything is shown in the video

[@congestiontv]

Another one saved. It's always bad when keys are missing. I'm sure you'll find a decent solution. Thank you for the video.

[@Arcticretro]

You bet. Got an original one from Noel :)

[@davedobbs]

I suspect that you still have an issue somewhere in the voltage conversion circuit as the picture is only black and white. The video encoder chip will only output a colour signal when the 12v line is working correctly. It would probably be worth removing all the lower RAM until this (and the -5v) line is confirmed as working, as the 4116 ram ICs tend to fail prematurely if run without these voltages present. It would also be worth confirming that the new previously good TR4 hasn't now become faulty as these tend to fail if there any faulty 4116 ram present when power is applied. I suspect this is more likely than both of your ULAs being faulty.

[@G7VFY]

You should try the cooler running switching regulator substitute for the 7805 and similar regulators. No heatsink required.

[@Arcticretro]

Thanks for the tip!

[@pe1dnn]

The plus case said Upgraded. This was an option for rubber key ZX Spectrum owners to upgrade to the plus case. It was a kit and the owner just moved the motherboard from the rubber key case to the Plus. That's also why the reset switch has this strange soldering to the wire. That is also why your ZX Spectrum board is an early Issue 2 board, which was the board of the first mass produced (rubber key) ZX Spectrums. It also has a older ULA and I think you even have an early Issue 2 board because the botch fix on an Issue 2 is normally a transistor on top of the CPU and not a resistor and a diode like you have. And before troubleshooting always check the 12V and -5V first because without those voltages the 4116 chips will die very soon in a few seconds. It not present then TR4 and TR5 need to be replaced.

[@Arcticretro]

Thanks for the info!

[@patzik1910]

I was thinking the same, your spot on. Just wanted to add that the ULA’s also have different resistors on 4 places. @Tommy, there is repair guide on spectrumforeveryone that might help you, also there are some good KZbin video’s by zxzigg for initial diagnosis before turning on the speccy. Also regarding swapping ic’s, don’t put a good ic in a possible bad system, put the suspected bad ic in the known good system. It would have been better to put the ula of the system you were working on in the know good zx spectrum.

[@pet.a.928]

I am surprised you did not check the other voltages on the spectrum it also used -5 -12 and +12 volts for the ram.

[@Arcticretro]

Actually I did later. I did not film everything

[@pe1dnn]

When you used the diagnostic EPROM, did you modify the board? The ZX Spectrum ROM is almost compatible with a 27128 EPROM but not completely. There is a simple mod with 2 diodes and a resistor to make is compatible, the enable signals on a 27128 EPROM are different from the ZX ROM and even there are 2 versions of the ZX ROM (same contents but different chips) and the main board has bridges to select the correct type that is installed. That's also where the EPROM mod has to me made.

[@Arcticretro]

No, was not aware of that. I'll check into that next time :) Thanks for the insight!

[@staalklang]

You need a PEX plate from wham bam so the tiny parts stick when printing.

[@Arcticretro]

Thanks!

[@NoelsRetroLab]

Nice repair. Glad you got it working. By the way, from the look of the video signal, I think the capacitors are starting to fail. I'm not one to replace capacitors all the time like some people, but unless it's some weird tuning on your display, that image should be a lot cleaner than that. Did you receive the shift key I sent you yet? 🙂

[@Arcticretro]

Thanks Noel. Yes, thank you for the shift key. Just got it the other day :)

[@patzik1910]

This is and issue 2 board that has the 2 tuning capacitors. The picture in my experience is always a bit worse than the other models. Getting the caps properly tuned is also a pain, and they drift so next time you switch on they might need tuning again.

[@AndrewTubbiolo]

Wow, Norway is so beautiful. It's 110 F 38 C in Tucson Az USA. Wheeeee.

[@Arcticretro]

That is too hot for me!

[@tenminutetokyo2643]

Yes but it’s a dry heat.

[@AndrewTubbiolo]

@@tenminutetokyo2643 We like to tell ourselves that. Sometimes it's even true.

[@natireson4140]

👍

[@RudysRetroIntel]

Excellent video as always. Could you tell us what the EPROM you are using to make the diagnostic ROM? Also, are you using the DiagROM.v59 file? Thank you for sharing.

[@Arcticretro]

I use a Minipro TL866 II clone that I got on Ali express. Works great. Costed like 60 USD

[@RudysRetroIntel]

@@Arcticretro Sorry, I mean what size and manufacturer of the EPROM itself. Thanks for sharing

[@CommodoreVic20]

Is there a part two?

[@Arcticretro]

Yes. Check out "Building a ZX Spectrum diagnostics card to try to fix my ZX Spectrum Plus"

[@CommodoreVic20]

Thanks, I actually found it after I posted this. Love your videos - glad you got it sorted.

[@byteforever7829]

If it had been the ula chip faulty you can buy vla82 I believe is a replacement fpga version, doesn't get as hot and used less power too 😀

[@horusfalcon]

Thanks for sharing this data.

[@Arcticretro]

Thanks! I will order chips after the vacation

[@tenminutetokyo2643]

DOOD!