ZX Spectrums problems : diagnostic software ?
- 1024MAK
- Posts: 5103
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX Spectrums problems : diagnostic software ?
Yes, very frustrating!
Hence why you have me stumped as well...
If the ROM is in a socket, remove it. Power up the board with it not fitted and take a photo of the screen.
Mark
Hence why you have me stumped as well...
If the ROM is in a socket, remove it. Power up the board with it not fitted and take a photo of the screen.
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.
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.
Re: ZX Spectrums problems : diagnostic software ?
Here is the photo of the display without ROM :
- 1024MAK
- Posts: 5103
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX Spectrums problems : diagnostic software ?
Leave it running for say 20 to 30 minutes, keep checking to see if the pattern stays the same.
Mark
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.
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.
Re: ZX Spectrums problems : diagnostic software ?
The red, on the blue columns, moves.
I will now try to let it run for 30 minutes.
I will now try to let it run for 30 minutes.
- 1024MAK
- Posts: 5103
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX Spectrums problems : diagnostic software ?
Yeah, it will. The Z80 is constantly executing RST38h, which pushes the contents of the PC (program counter) to the stack. But as we never take anything from the stack, the stack pointer in the Z80 continues to grow. The result is that the same two byte value ends up filling every RAM location. The Z80 will just keep doing this, constantly looping through memory until you remove power...
It’s a good quick test.
Mark
It’s a good quick test.
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.
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.
Re: ZX Spectrums problems : diagnostic software ?
After having wait for about 25 minutes, here is the result :
the red things, which appear on the blue columns, flash every second :
the columns are totally blue for one second, then the red appears on them for one second, then the columns are totally blue for one second, and so on ...
the red things, which appear on the blue columns, flash every second :
the columns are totally blue for one second, then the red appears on them for one second, then the columns are totally blue for one second, and so on ...
Re: ZX Spectrums problems : diagnostic software ?
I finally replaced TR3, no difference (but I was not expecting much as the clock is present on the Z80).
So still investigating ... Here is the current behaviour of the Spectrum : I turn it on, it displays the sinclair copyright. If I don't do nothing with it, then, after about one minute, it resets itself and go back to the sinclair copyright. And so on ...
So still investigating ... Here is the current behaviour of the Spectrum : I turn it on, it displays the sinclair copyright. If I don't do nothing with it, then, after about one minute, it resets itself and go back to the sinclair copyright. And so on ...
Re: ZX Spectrums problems : diagnostic software ?
I wonder if my problem could come from the RAM capacitors ...
Last edited by dizzy33 on Mon May 04, 2020 5:41 pm, edited 1 time in total.
Re: ZX Spectrums problems : diagnostic software ?
That's very strange, here are my new investigations :
by replacing the RAM chips by others (old and new ram chips are known as working), and mixing different brands of RAM chips, I could find a RAM chips set which is "quite" working fine.
I mean that with this set of selected RAM chips, the Spectrum does almost work fine :
when I start a game, it works fine for a few minutes then, some graphical bugs appear on the very left side of the screen. But the game still works fine.
If I run my Diag ROM, it does not find any RAM chip failing. But if I ask to my Diag ROM to run some programs execution tests in lower RAM, then the test fails ...
So I feel like a small electronic component (not an IC) let the lower RAM bug. I measured the voltages on all lower RAM chips and they are OK.
That's why I'm wondering if this problem could come from the RAM capacitors (C1-C8) .
Does anyone have an opinion about this (Mark seems to be unavailable these last weeks, I hope he is well) ?
by replacing the RAM chips by others (old and new ram chips are known as working), and mixing different brands of RAM chips, I could find a RAM chips set which is "quite" working fine.
I mean that with this set of selected RAM chips, the Spectrum does almost work fine :
when I start a game, it works fine for a few minutes then, some graphical bugs appear on the very left side of the screen. But the game still works fine.
If I run my Diag ROM, it does not find any RAM chip failing. But if I ask to my Diag ROM to run some programs execution tests in lower RAM, then the test fails ...
So I feel like a small electronic component (not an IC) let the lower RAM bug. I measured the voltages on all lower RAM chips and they are OK.
That's why I'm wondering if this problem could come from the RAM capacitors (C1-C8) .
Does anyone have an opinion about this (Mark seems to be unavailable these last weeks, I hope he is well) ?
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Re: ZX Spectrums problems : diagnostic software ?
Replacing those capacitors is recommended to help reduce jail-bars (https://www.sinclairzxworld.com/viewtopic.php?t=3059) so I would certainly give it a go regardless.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA