ZX Spectrums problems : diagnostic software ?
- 1024MAK
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Re: ZX Spectrums problems : diagnostic software ?
I will help where I can.
First though, just play with it and get used to the controls and the effect they have.
What type of probe(s) were supplied? Do they have a switch marked 1:10 or similar?
With non-complex repetitive waveforms, adjust the signal level, timebase and trigger controls until you get a stable steady waveform. Try the CPU clock signal on Z80 pin 6. But note that the ULA sometimes pauses this when it wants to pause the CPU when it requires priority access to the screen RAM.
Unfortunately in a computer, like the ZX Spectrum most signals are complex so a different method has to be used.
If I find time, I’ll post up some example waveforms.
Mark
First though, just play with it and get used to the controls and the effect they have.
What type of probe(s) were supplied? Do they have a switch marked 1:10 or similar?
With non-complex repetitive waveforms, adjust the signal level, timebase and trigger controls until you get a stable steady waveform. Try the CPU clock signal on Z80 pin 6. But note that the ULA sometimes pauses this when it wants to pause the CPU when it requires priority access to the screen RAM.
Unfortunately in a computer, like the ZX Spectrum most signals are complex so a different method has to be used.
If I find time, I’ll post up some example waveforms.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
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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 ?
I already played with it, measured some audio signals, etc ... Yes my probe has a "1x" "10x" switch.
All I need is just you to tell me on wich pin of which component I should attach my probes and which signal should I see.
All I need is just you to tell me on wich pin of which component I should attach my probes and which signal should I see.
Re: ZX Spectrums problems : diagnostic software ?
Hello Mark,
today my Spectrum does not start anymore (I didn't try it for about a month). Here is how looks the display when I power it up :
As you requested I connected my oscilloscope to pin 6 (clock) of the Z80, here is the result :
What do you think about this result ?
today my Spectrum does not start anymore (I didn't try it for about a month). Here is how looks the display when I power it up :
As you requested I connected my oscilloscope to pin 6 (clock) of the Z80, here is the result :
What do you think about this result ?
Re: ZX Spectrums problems : diagnostic software ?
I tested the ULA voltages. Here is my (bad) results :
on pin 13, I should have 5v. I only have 3.5v -> BAD
on pin 14, I should have 5v. I have 5v -> OK
What could be responsible of this low voltage for pin 13 of my ULA ? (as a reminder my motherboard is an issue 2).
EDIT : finally this 3.5v may be normal ... Here : http://www.breakintoprogram.co.uk/compu ... rdware/ula
pin 13 is notified with 5v ... But here : https://spectrumforeveryone.com/wp-cont ... Manual.pdf it's said we should have 3v ... So I guess the "breakintoprogram.co.uk" pinout is wrong.
So I really need help here ...
on pin 13, I should have 5v. I only have 3.5v -> BAD
on pin 14, I should have 5v. I have 5v -> OK
What could be responsible of this low voltage for pin 13 of my ULA ? (as a reminder my motherboard is an issue 2).
EDIT : finally this 3.5v may be normal ... Here : http://www.breakintoprogram.co.uk/compu ... rdware/ula
pin 13 is notified with 5v ... But here : https://spectrumforeveryone.com/wp-cont ... Manual.pdf it's said we should have 3v ... So I guess the "breakintoprogram.co.uk" pinout is wrong.
So I really need help here ...
- 1024MAK
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Re: ZX Spectrums problems : diagnostic software ?
That’s a classic RAM failure screen. The ROM code found a problem and stopped (well, it actually runs an infinite loop).
That’s not quite right!
I’ll try to find time to post a photo of what it should look like later....
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.
- 1024MAK
- Posts: 5104
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX Spectrums problems : diagnostic software ?
Both those are acceptable results. Pin 13 is fed via a resistor so the voltage will be lower.
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 ?
Thanks a lot Mark. But I think I have found a RAM problem.
I don't understand as at the beginning of my investigations, I already have tested the RAM voltages, and as far as I remember they were OK.
Now, here is the result I have for IC6 and IC13 (didn't test all the RAM but I guess it's the same issue everywhere) :
PIN 1 = -4.4v -> OK.
PIN 9 = +5v -> OK.
PIN 8 = 0V -> BAD -> should have 12V ...
I don't understand as at the beginning of my investigations, I already have tested the RAM voltages, and as far as I remember they were OK.
Now, here is the result I have for IC6 and IC13 (didn't test all the RAM but I guess it's the same issue everywhere) :
PIN 1 = -4.4v -> OK.
PIN 9 = +5v -> OK.
PIN 8 = 0V -> BAD -> should have 12V ...
- 1024MAK
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Re: ZX Spectrums problems : diagnostic software ?
Going purely on the screen display, it’s possibly IC12 in the lower RAM that has failed.
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.
- 1024MAK
- Posts: 5104
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: ZX Spectrums problems : diagnostic software ?
Are you sure? With no +12V supply none of the lower RAM chips will work... (and loss of the +12V rail will also affect the video output).dizzy33 wrote: ↑Sun Apr 19, 2020 12:42 pm Thanks a lot Mark. But I think I have found a RAM problem.
I don't understand as at the beginning of my investigations, I already have tested the RAM voltages, and as far as I remember they were OK.
Now, here is the result I have for IC6 and IC13 (didn't test all the RAM but I guess it's the same issue everywhere) :
PIN 1 = -4.4v -> OK.
PIN 9 = +5v -> OK.
PIN 8 = 0V -> BAD -> should have 12V ...
A reminder that the pin out is here.
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 ?
Mark, yes, you are right, my diagnostic cartridge says IC12 is defective, but if I replace it, then it will say another one is.
That's my problem since the beginning of my investigations. Something is wrong on my motherboard which let the RAM goes bad.
Now I don't have no 12v anymore on PIN 8 of my RAM chips, I had it at the begining of my investigations. I guess I should test TR4, right ?
If yes, how should I proceed to check if it's good or not ?
Any other component may be related to the lack of 12v in my RAM ?
EDIT : I have found this video which shows how to test TR4 with an oscilloscope ... Will try it ...
https://www.youtube.com/watch?v=rZ641nqT8F0
That's my problem since the beginning of my investigations. Something is wrong on my motherboard which let the RAM goes bad.
Now I don't have no 12v anymore on PIN 8 of my RAM chips, I had it at the begining of my investigations. I guess I should test TR4, right ?
If yes, how should I proceed to check if it's good or not ?
Any other component may be related to the lack of 12v in my RAM ?
EDIT : I have found this video which shows how to test TR4 with an oscilloscope ... Will try it ...
https://www.youtube.com/watch?v=rZ641nqT8F0