Spectrum 48k ULA replacement

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Spectrum65535
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Joined: Tue Feb 16, 2021 8:19 pm
Location: Warrington

Spectrum 48k ULA replacement

Post by Spectrum65535 »

Hi all
Bought a Spectrum 48k issue 2 listed as not working, just come to renovate it and noticed they have put a 6C001E-7 ULA in the socket instead of the usual 5C112E, will this work without any other component change?
I’m asking because I don't trust the repairs they did to the board, due to the fact they put an NEC Rom in and not changed the links over from Hitachi, I haven’t powered this board up till I’m sure everything is right.
Simon
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1024MAK
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Re: Spectrum 48k ULA replacement

Post by 1024MAK »

Later ULA chips made by Ferranti are generally backwards compatible so can be fitted in older issue boards.

Mark
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Spectrum65535
Posts: 14
Joined: Tue Feb 16, 2021 8:19 pm
Location: Warrington

Re: Spectrum 48k ULA replacement

Post by Spectrum65535 »

Thanks Mark
I found a list of which ULA went in what machine, and you are correct, although this ULA I believe is dead, I just get a black screen with white lines across it, like static, I have replaced the Video decoder (LM1889), the Z80, all DC-DC converter transistors, although all the voltages were in tolerance and still are, I also re capped it by default. I have a Retroleum Diagrom sat in there now, not a beep out of it. I have ordered the correct ULA, I shall continue when that arrives, unless you have any other theories? :roll:
Simon
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1024MAK
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Re: Spectrum 48k ULA replacement

Post by 1024MAK »

Is there a 3.5MHz clock signal on pin 32 of the ULA?

What DC voltage do you get on pins 13 and 14 of the ULA?

Are all the socket contacts okay?

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Spectrum65535
Posts: 14
Joined: Tue Feb 16, 2021 8:19 pm
Location: Warrington

Re: Spectrum 48k ULA replacement

Post by Spectrum65535 »

Pins 13 and 14 are 4.98 volts, and hello, no activity on pin 32, checked the solder side and found a minute solder splash pulling it to ground, cleaned that off, hurrah! Activity, put the new ULA in and it lives again, well, limps a bit, some lower ram failure due to dodgy chip sockets (See photo), I think the original repairer best not give up the day job :lol:

Cheers mark
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Simon
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