Issue 3B - White screen, Retroleum smart card runs - Screen corrupt

[DR400]

Hi, first post here, but a long time lurker! and always find out something new.

I have a Issue3B, it has never been opened/modded or powered on for 15+ years, opened to do the composite mod, powered on and got the Sinclair message OK, powered on a second time and it now starts to a white screen and border, no Sinclair message, plugged in my Retroleum Smart card and the diag rom screen is shown, see pic 1, but the text is corrupt and looks like is being repeated in the next character.

The Ram test runs and does not report any errors, but each character is doubled?, usually just one coloured square, not two as shown in PIC 2

PIC 3 shows the SDmart Card menu or a working issue 2 machine, PIC 4 is the same menu on the faulty 3B

Diags so far - All voltages are correct and within the limits on various posts on this site, disabled the the upper 32RAM with the 5v to the 74ls32 trick, checked for shorts etc, stray solder blobs etc.

Was going to swap the ULA as a test with the one in my working Issue 2 , but not sure that's the problem, are the ULA's swappable between issue 2's &3's ?

I have a spare Zilog Z80, current is a NON socketed NEC, so don't want to de-solder unless it gets to that stage, also have spare RAM chips as well as a Retroleum NEBULA replacement to try, but the existing socket needs replacing to use this.

Thanks in advance for any clues as what to try next.

Regards

PIC 1


PIC 2



PIC 3



PIC 4

[Ast A. Moore]

Was going to swap the ULA as a test with the one in my working Issue 2 , but not sure that's the problem, are the ULA's swappable between issue 2's &3's ?

Generally, ULAs are backward compatible. That is, you can use a later version of the ULA in any board that came out before it, but not the other way around. So you can test the ULA from your Issue 3 by sticking it into your working Issue 2, but using the ULA from an Issue 2 in a later board may not work.

ULAs marked 6C001E-6 and 6C001E-7 will work in any 48/16K Speccy. 5C112E were used on most Issue 2 boards and may not work in later board revisions (although it’s not set in stone).

[DR400]

Thank you for the reply, I put the ISSUE 3 ULA (faulty) into my working ISSUE 2 and get exactly the same white border and screen , so it looks like the ULA is faulty, so will replace with the NEBULA tomorrow.

Thank you for your help
Regards
DR400

PIC is of the offending ULA from Issue 3A PCB

Are there any other 'new' replacement ULA's out there similar to the NEBULA?

[MrClump]

Are there any other 'new' replacement ULA's out there similar to the NEBULA?

There is also the vLA82, which you can get from Retro Revival in the UK (currently out of stock though). It's more compact than the Nebula, but a little more costly and less readily available.

I have both and they both work absolutely fine, although if you're in the UK there is the benefit that you'd be buying the Nebula from the guy that actually makes them. He fixed mine when I blew up the CPLD.

[DR400]

Are there any other 'new' replacement ULA's out there similar to the NEBULA?

There is also the vLA82, which you can get from Retro Revival in the UK (currently out of stock though). It's more compact than the Nebula, but a little more costly and less readily available.

I have both and they both work absolutely fine, although if you're in the UK there is the benefit that you'd be buying the Nebula from the guy that actually makes them. He fixed mine when I blew up the CPLD.

Thank you Mr Clump, I am UK based and RETROLEUM is my usual place for parts, thanks for the info, will keep watch for return of stock on the vLA82 site.
Regards
DR400

Wish I had half the knowledge these reverse engineers have, I do a composite mod and think I have invented the ZX Spectrum

[Ast A. Moore]

Are there any other 'new' replacement ULA's out there similar to the NEBULA?

Sometimes it’s actually cheaper to get a few “untested” Spectrum boards and harvest a ULA from them, than to buy a modern ULA replacement.