Sinclair Spectrum ZX stuck on random graphics colours. - UK Vintage Radio Repair and Restoration Discussion Forum

Llwyngwern · 12th Aug 2013, 6:25 pm

Hiya all ,
Just wondering if someone could help me.

I have got a spectrum zx 128 +2; it did work but then wouldn't go back to the main loading page and is stuck on random graphics colours. I have tried resetting it and leaving it off but still stuck on the colours.

Thanks .

Laurdys · 12th Aug 2013, 8:16 pm

try resetting the machine while holding the break key down. this should produce a test tone and pattern.

SiriusHardware · 12th Aug 2013, 11:05 pm

Quote:

Originally Posted by Llwyngwern

Hiya all just wondering if someone could help me , I have got a spectrum zx 128 +2 it did work but then wouldn't go back to the main loading page and is stuck on random graphic's colours , have tried resetting it and leaving it off but still stuck on the colours thanks .

What Laurdys said, but if that doesn't produce a sensible result I'm afraid the multiple flashing coloured blocks symptom is generally a sign that there is a serious system-stopping fault. Typically this was what you would see if the ULA chip had failed, for example.

If you are lucky, it's just an IC jolted half way out of a socket, so you may as well have a look and try pushing any ICs which are in sockets firmly back in.

DragonForce · 14th Aug 2013, 10:39 pm

Right, first things first. Are we talking about a black +2 or a grey +2? The grey +2 is very different internally from the black version (known as the +2A or +2B)

The Black +2 doesn't have a ULA as such, it has an ASIC chip, and if that's gone, the only source of spare parts is a scrap +2A machine. That's also true of the grey +2 to be honest, but the ASIC is a small rectangular surface mount IC and needs pretty specific soldering skills to replace.

The good news (sort of) is that these ULA/ASIC chips are pretty hardy beasts and your problem is probably down to a bad RAM chip (or three).

First thing to do is find out why the RAM failed in the first place - this could be down to a bad capacitor - so recap ALL the electrolytics before you power it up again. Then, in the case of a grey +2, you should find a ZTX 650 transistor - test it! Replace if you need to. If you need to replace the ZTX 650, find out why it blew - check the small coil for shorted turns, Zener diodes etc. A shorted capacitor could cause the magic smoke to escape also, but don't be complacent about it, TEST IT ALL!

If it's a black +2, test the PSU for the correct voltage levels, remember these have electrolytics inside them too, and so you's best replace those too.

Assuming you now have the correct voltages on the RAM IC's (consult the datasheets for the specific pins to test) and rectify any faults found if the voltages are out.

OK, if it's a Black +2, you will probably need up to 4x 4464 RAM chips - you can grab those off of some old ISA graphics cards.

If it's a grey +2, you will need up to 16x 4164 RAM chips.

Carefully remove your old RAM chips - use either a hot air gun (and be VERY careful) or use your favoured method of desoldering chips. FIT SOCKETS and then replace with new RAM.

This will probably get you working again. If you haven't understood a word I've said, then don't mess with it - there is a guy who repairs these on Ebay, just search for Spectrum Repair. (No, it isn't me).

12th Aug 2013, 6:25 pm	#1
Llwyngwern Retired Dormant Member Join Date: Aug 2013 Location: Carmarthenshire Posts: 1	Sinclair Spectrum ZX stuck on random graphics colours. Hiya all , Just wondering if someone could help me. I have got a spectrum zx 128 +2; it did work but then wouldn't go back to the main loading page and is stuck on random graphics colours. I have tried resetting it and leaving it off but still stuck on the colours. Thanks . Last edited by Mike Phelan; 13th Aug 2013 at 8:46 am. Reason: Typos.

12th Aug 2013, 8:16 pm	#2
Laurdys Pentode Join Date: May 2009 Location: Stockton-on-Tees, County Durham, UK. Posts: 154	Re: Sinclair zx spectrum try resetting the machine while holding the break key down. this should produce a test tone and pattern. __________________ If it can be built, it can also be fixed. Last edited by Station X; 12th Aug 2013 at 9:52 pm. Reason: Posts moved to new thread.

14th Aug 2013, 10:39 pm	#4
DragonForce Retired Dormant Member Join Date: Nov 2011 Location: Bristol, UK. Posts: 168	Re: Sinclair Spectrum ZX stuck on random graphics colours. Right, first things first. Are we talking about a black +2 or a grey +2? The grey +2 is very different internally from the black version (known as the +2A or +2B) The Black +2 doesn't have a ULA as such, it has an ASIC chip, and if that's gone, the only source of spare parts is a scrap +2A machine. That's also true of the grey +2 to be honest, but the ASIC is a small rectangular surface mount IC and needs pretty specific soldering skills to replace. The good news (sort of) is that these ULA/ASIC chips are pretty hardy beasts and your problem is probably down to a bad RAM chip (or three). First thing to do is find out why the RAM failed in the first place - this could be down to a bad capacitor - so recap ALL the electrolytics before you power it up again. Then, in the case of a grey +2, you should find a ZTX 650 transistor - test it! Replace if you need to. If you need to replace the ZTX 650, find out why it blew - check the small coil for shorted turns, Zener diodes etc. A shorted capacitor could cause the magic smoke to escape also, but don't be complacent about it, TEST IT ALL! If it's a black +2, test the PSU for the correct voltage levels, remember these have electrolytics inside them too, and so you's best replace those too. Assuming you now have the correct voltages on the RAM IC's (consult the datasheets for the specific pins to test) and rectify any faults found if the voltages are out. OK, if it's a Black +2, you will probably need up to 4x 4464 RAM chips - you can grab those off of some old ISA graphics cards. If it's a grey +2, you will need up to 16x 4164 RAM chips. Carefully remove your old RAM chips - use either a hot air gun (and be VERY careful) or use your favoured method of desoldering chips. FIT SOCKETS and then replace with new RAM. This will probably get you working again. If you haven't understood a word I've said, then don't mess with it - there is a guy who repairs these on Ebay, just search for Spectrum Repair. (No, it isn't me).