Poorly issue two Spectrum

Lardo Boffin
Posts: 1432
Joined: Sat Nov 26, 2016 2:42 am

Poorly issue two Spectrum

Post by Lardo Boffin »

I just got an issue two Spectrum which doesn’t boot, as below. The two lower RAM chips marked with splodges get very hot quite quickly so I’m assuming are faulty?

I have a couple of 4116s somewhere but is there anything I should check / change first to avoid them also becoming broken?

7EF8AFF1-9FCC-4CB4-9705-6B1EE8D856EE.jpeg

Thanks!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Toastrack
Lardo Boffin
Posts: 1432
Joined: Sat Nov 26, 2016 2:42 am

Re: Poorly issue two Spectrum

Post by Lardo Boffin »

Looks like it lead an interesting life - pretty sure that isn’t the original ULA (the serial number is 001-057303) and also an interesting daughter board near the Z80. Part of the 48K glue logic?

2ECB171E-6711-47F1-9A22-4376F8303D10.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Toastrack
Lardo Boffin
Posts: 1432
Joined: Sat Nov 26, 2016 2:42 am

Re: Poorly issue two Spectrum

Post by Lardo Boffin »

Is the broken trace / gap intentional?

9D65155A-E23F-4D0A-827D-B4537091BC99.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Toastrack
User avatar
Erm
Posts: 201
Joined: Thu Jun 20, 2019 7:07 pm

Re: Poorly issue two Spectrum

Post by Erm »

I had one with a little board like that once. It seemed to be an adapter so that a different type of 74X chip (with different pin out) could do the same job as the one that should go in that socket. I replaced it with whatever should normally go in that socket just because it looked tidier.

You don't by any chance have a very early ULA spare? I have an issue 1 board with a later ULA and would like to revert it to original (with the Spider mod).
I'm Chris, a Brit in Germany (Chr$ on the QL forum).
Lardo Boffin
Posts: 1432
Joined: Sat Nov 26, 2016 2:42 am

Re: Poorly issue two Spectrum

Post by Lardo Boffin »

Erm wrote: Tue Apr 20, 2021 4:52 pm You don't by any chance have a very early ULA spare? I have an issue 1 board with a later ULA and would like to revert it to original (with the Spider mod).
Sorry I don’t have one. I bought this mainly in the hope it would have one being a fairly low serial number!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Toastrack
User avatar
Erm
Posts: 201
Joined: Thu Jun 20, 2019 7:07 pm

Re: Poorly issue two Spectrum

Post by Erm »

Everyone wants a 5C102E!
I'm Chris, a Brit in Germany (Chr$ on the QL forum).
Lardo Boffin
Posts: 1432
Joined: Sat Nov 26, 2016 2:42 am

Re: Poorly issue two Spectrum

Post by Lardo Boffin »

Replacing the two RAMs means it now boots fine to the Sinclair logo!

Is there anything else I should check before leaving it switched on for any length of time? Presumably something caused the chips to fail in the first place.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Toastrack
User avatar
Erm
Posts: 201
Joined: Thu Jun 20, 2019 7:07 pm

Re: Poorly issue two Spectrum

Post by Erm »

Lardo Boffin wrote: Wed Apr 21, 2021 2:19 pm Replacing the two RAMs means it now boots fine to the Sinclair logo!

Is there anything else I should check before leaving it switched on for any length of time? Presumably something caused the chips to fail in the first place.
I think you should be fine (if the 3 voltages are good). The 4116's tend to just fail on their own, quite a lot.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Poorly issue two Spectrum

Post by 1024MAK »

Lardo Boffin wrote: Tue Apr 20, 2021 2:48 pm Looks like it lead an interesting life - pretty sure that isn’t the original ULA (the serial number is 001-057303) and also an interesting daughter board near the Z80. Part of the 48K glue logic?
Check the +9V, +5V, +12V and most importantly the -5V supplies.

The +9V (nominal) MUST be less than 11.9V unless the power section has been upgraded to this standard.

The -5V must be between -4V and -5.5V.

Type in

Code: Select all

 PRINT PEEK 23732 + PEEK 23733 * 256
Then Run a diagnostic test to confirm that all the RAM is okay. A tape based version is fine.

Definitely not the original ULA, so it’s been repaired at some point in the past. Likely started off as a 16k machine.

The daughter board allows OKI DRAM chips to be used instead of Texas Instruments DRAM chips, as the issue two board was not designed with as many link options. It’s not so much glue logic, rather the wiring of the address lines via the multiplexer chips. I can’t remember there being a track break, but then, I don’t have an operational Speccy with one of those daughter boards... But given that the other end of that track goes to another pin, yes, I think it’s intentional.

Mark
Lardo Boffin
Posts: 1432
Joined: Sat Nov 26, 2016 2:42 am

Re: Poorly issue two Spectrum

Post by Lardo Boffin »

So I get:

-4.39V
5.01 V
12.2V

The 9V (measured on the legs of the 7805, red to left leg, black to middle leg, looking down) is 8.9V. But I am using a modern PSU. Will find an original one and test again.

Where is best to measure the 9V?

Assuming I got a good measurement of the 9V all is looking to be ok.

The ULA case gets too hot to comfortably touch after a minute or two. Not sure how quickly that should heat up?
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Toastrack
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