Recently, I recovered a QL. A few days later, it started crashing at startup, and now it doesn't work at all.
The symptoms are as follows: when I connect the power supply, the video pattern appears on the screen, but unfortunately, it never completes. At the end of the random pattern, a white strip appears at the top of the screen, while the rest of the display remains in a random pattern. And that’s it—no further response.
It doesn't respond to the reset button. Occasionally, it reaches the F1/F2 screen, but the keyboard doesn't register any input, and it still doesn’t respond to reset.
Before replacing any ICs, I’d like to confirm where the fault is. Unfortunately, I currently only have a multimeter and a 200kHz oscilloscope.
Does anyone have any suggestions or ideas?
Thanks in advance!
SOS My QL is dying
Re: SOS My QL is dying
Start by re-seating all ic's , and verify if the 68 is warming up .
be very carefull when lifting them !!
be very carefull when lifting them !!
Zx80-1/3k exp.-zx81-16k exp.- Spectrum 48 - Spectrum+ -Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo - Velleman interface system - Currah microspeech - Ql - Miracle 512k exp.- Ql printer - Cst Qdisk interf.- Qubide - Double 3.5 floppy- Minerva - Ice 1.9 - Ql Usb mouse adapter - Qimi-and much more .
Re: SOS My QL is dying
Which Rom are you using? I think my first thought is ZX8302 that would cause all those issues.
Re: SOS My QL is dying
Thanks! My QL has a JM ROM and it's an Issue 6 board. I’ll try replacing the 8302—fortunately, I have a spare one.
I suspect there may be a bus-related issue. The last time I powered it on, after the random pattern appeared, it made some unusual noises and displayed a vertical pattern before crashing. Also, the microdrives activate randomly during startup, which doesn’t seem normal.
I think the 8301 is working, since the graphics appear to be generated correctly—VSync, HSync, and all video signals are present.
I suspect there may be a bus-related issue. The last time I powered it on, after the random pattern appeared, it made some unusual noises and displayed a vertical pattern before crashing. Also, the microdrives activate randomly during startup, which doesn’t seem normal.
I think the 8301 is working, since the graphics appear to be generated correctly—VSync, HSync, and all video signals are present.
Re: SOS My QL is dying
I’ve replaced both the 8302 and the 8049. There's been a slight improvement—now it occasionally manages to boot, and sometimes even responds to the reset button.
However, after a few seconds (no more than 5), the system starts to degrade and eventually crashes, showing random values in memory (and video, of course) and becoming unresponsive again.
However, after a few seconds (no more than 5), the system starts to degrade and eventually crashes, showing random values in memory (and video, of course) and becoming unresponsive again.
Re: SOS My QL is dying
I'm wondering if you have an unstable voltage - is this machine still running with the 5v regulator? If it is, you could try replacing that - they are not soldered (usually) so it's a just a matter of opening the case, removing the screw that holds the regulator to the heatsink - and then do your replacement.
Re: SOS My QL is dying
When it fails...
Could you touch the RAM ICs with your hand and feel any heat in any IC?
Could you touch the RAM ICs with your hand and feel any heat in any IC?
Re: SOS My QL is dying
Latest update:
The PSU is working fine, and the 7805 is also OK, but the situation remains the same.
I’ve observed that when the QL crashes, the DSMCL signal stays high (while KILLH is low). Curiously, everything seems to stop once DSMCL goes high. What’s more, this appears to be timed: during the first 10 seconds after power-on, the reset button works normally—but then the system crashes.
According to the service manual, a high level on DSMCL disables the 8301, which could explain why the system becomes unresponsive.
I’ve already replaced the 8302, although I can’t be sure the replacement is working properly. I’ll try to explore the communication lines to see if I can spot anything unusual.
Unfortunately, I won’t be able to continue troubleshooting until Wednesday.
Many thanks to all of you for your suggestions and comments!
The PSU is working fine, and the 7805 is also OK, but the situation remains the same.
I’ve observed that when the QL crashes, the DSMCL signal stays high (while KILLH is low). Curiously, everything seems to stop once DSMCL goes high. What’s more, this appears to be timed: during the first 10 seconds after power-on, the reset button works normally—but then the system crashes.
According to the service manual, a high level on DSMCL disables the 8301, which could explain why the system becomes unresponsive.
I’ve already replaced the 8302, although I can’t be sure the replacement is working properly. I’ll try to explore the communication lines to see if I can spot anything unusual.
Unfortunately, I won’t be able to continue troubleshooting until Wednesday.
Many thanks to all of you for your suggestions and comments!
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martyn_hill
- QL Wafer Drive
- Posts: 1064
- Joined: Sat Oct 25, 2014 9:53 am
Re: SOS My QL is dying
Hi there!
With regard to DSMCL remaining high - bear in mind that this signal, in the absence of anything holding it high, is merely a resistor-coupled DSL as generated by the CPU itself.
You might want to measure DSL directly to see whether or not it too is stuck inactive/high.
On the Iss6/7 boards, the HAL and TR8 are the only components responsible for disabling the 8301 (via KILLH as you noted being inactive), so unless some other electrical short (to Vcc) affecting DSMCL, then it would indicate that the CPU itself is stalling somehow.
One such electrical fault could be the transistor responsible for disabling DSMCL (pulling it high) based on the HAL's KILLH, TR8. That might be an easy replacement/test to start with...
Alternatively, the CPUCLK signal (as generated via the 15MHz crystal oscillator, then buffered/halved via the 8301) might be failing.
Another thought, less likely - could the BRL signal be triggering (active/held low) causing the CPU to relinquish the bus - effectively stalling until the CPU until the bus is released? In this state, the CPU should send DS in to high impedance, but that might be measured as high, depending on your test equipment.
Good luck!
With regard to DSMCL remaining high - bear in mind that this signal, in the absence of anything holding it high, is merely a resistor-coupled DSL as generated by the CPU itself.
You might want to measure DSL directly to see whether or not it too is stuck inactive/high.
On the Iss6/7 boards, the HAL and TR8 are the only components responsible for disabling the 8301 (via KILLH as you noted being inactive), so unless some other electrical short (to Vcc) affecting DSMCL, then it would indicate that the CPU itself is stalling somehow.
One such electrical fault could be the transistor responsible for disabling DSMCL (pulling it high) based on the HAL's KILLH, TR8. That might be an easy replacement/test to start with...
Alternatively, the CPUCLK signal (as generated via the 15MHz crystal oscillator, then buffered/halved via the 8301) might be failing.
Another thought, less likely - could the BRL signal be triggering (active/held low) causing the CPU to relinquish the bus - effectively stalling until the CPU until the bus is released? In this state, the CPU should send DS in to high impedance, but that might be measured as high, depending on your test equipment.
Good luck!