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Sinclair QL Diagnostic
Posted: Mon Jun 24, 2024 5:00 pm
by RWAP
All,
I have a QL here which has been in storage - I have removed and reinserted all of the socketed chips and replaced the membrane.
Turned it on and it starts up OK
However, neither microdrive responds to a command. The BEEP command also fails to do anything.
Has anyone come across anything like this before?
Re: Sinclair QL Diagnostic
Posted: Mon Jun 24, 2024 6:33 pm
by Derek_Stewart
Hi Rich,
Have you tried replacing the speaker unit.
Re: Sinclair QL Diagnostic
Posted: Mon Jun 24, 2024 7:45 pm
by tofro
That's a bit of a weird problem - and, in fact, it rather sounds like two independent ones:
BEEP is entirely under the control of the IPC - Nothing else must work in the QL than the IPC and its communications to the CPU for BEEP to work (of course, the speaker must...).
On the other hand, the IPC has nothing to do with Microdrives - they are nearly entirely controlled by the 8302 ULA. It is really hard to imagine a fault that would cause both problems.
I guess if you can verify that BEEP doesn't work, keyboard (also controlled by the IPC) and everything else is working?
Re: Sinclair QL Diagnostic
Posted: Mon Jun 24, 2024 10:04 pm
by Derek_Stewart
...so test the IPC, replace with Hermes, check the speaker, trace the sound circuit:
Here is the Issue 5/6 Sound circuit:
Re: Sinclair QL Diagnostic
Posted: Tue Jun 25, 2024 12:30 am
by martyn_hill
Hi there!
Given that the IPC (which handles the beeper, Serial input and the keyboard) is connected to the rest of the system/CPU via the 8302 ULA, and that ULA also directly handles the Microdrives, it seems likely that the 8302 is at least partially faulty.
That said, if the keyboard itself is responding as expected, then the comms between the ULA and the IPC must be working and the IPC at least partially working...
If the speaker cct proves to be OK (it's a simple transistor/resistor driven by a digital output of the IPC) I'd then suggest trying to source both a new IPC (or better still, a Hermes replacement as Derek suggests) and then a replacement 8302 (getting hard to find/expensive.)
When you say neither MDV respond, do you get zero activity from them, or that they spin-up but don't read the cartridges correctly?
Re: Sinclair QL Diagnostic
Posted: Tue Jun 25, 2024 7:54 am
by RWAP
martyn_hill wrote: Tue Jun 25, 2024 12:30 am
Hi there!
Given that the IPC (which handles the beeper, Serial input and the keyboard) is connected to the rest of the system/CPU via the 8302 ULA, and that ULA also directly handles the Microdrives, it seems likely that the 8302 is at least partially faulty.
That said, if the keyboard itself is responding as expected, then the comms between the ULA and the IPC must be working and the IPC at least partially working...
If the speaker cct proves to be OK (it's a simple transistor/resistor driven by a digital output of the IPC) I'd then suggest trying to source both a new IPC (or better still, a Hermes replacement as Derek suggests) and then a replacement 8302 (getting hard to find/expensive.)
When you say neither MDV respond, do you get zero activity from them, or that they spin-up but don't read the cartridges correctly?
I have tried swapping the 8049 from a working machine so my next guess was going to be the speaker itself.
The 8302 is more problematic, as I do not want to risk removing the one from my working QL. The microdrives simply do not respond to anything - as though there is no power at all.
Re: Sinclair QL Diagnostic
Posted: Tue Jun 25, 2024 8:44 am
by Pr0f
The Microdrives take their power from the 9v rail, from the power supply, which also feeds the main regulator.
If the rest of your QL has power, then the Microdrive units should also be seeing that power.
Re: Sinclair QL Diagnostic
Posted: Tue Jun 25, 2024 10:40 am
by Martin_Head
You might want to try removing the MDV1 unit and replacing it with the MDV2 unit. In case the ULA on MDV1 is faulty and blocking the MDV2 unit.
Re: Sinclair QL Diagnostic
Posted: Tue Jun 25, 2024 12:01 pm
by martyn_hill
Hi again Rich!
I'd also be tempted to reseat the existing 8302 - especially if the legs look in any way tarnished after so long in storage.
Given no MDV activity what-so-ever, either the 8302 is not managing the COMMS Clk and COMMS Data/out lines properly, or else one or more of the pair (PNP and NPN) of transistors that form the power drive cct on each MDV (as installed on the QL main board) are faulty.
That 9v rail should be working OK if the rest of the board is up and, even if it was below spec, the LED/Motor should start to light-up/ spin.
That said, if the 500mA linear regulator is dead on either MDV head-board, then the respective MDV ULAs might not be driving the COMMS Out signal which then drives both the power cct for its own drive, plus the next MDV's COMMS In, so as mentioned below, swapping over MDV2 for MDV1 would be a useful check. In so doing, you'd also get a good look at the inter-board connectors that join to the MDV head-board.
Along with the lack of beeper, a curious combination of errors indeed!
Re: Sinclair QL Diagnostic
Posted: Tue Jun 25, 2024 1:27 pm
by RWAP
martyn_hill wrote: Tue Jun 25, 2024 12:01 pm
Hi again Rich!
I'd also be tempted to reseat the existing 8302 - especially if the legs look in any way tarnished after so long in storage.
Given no MDV activity what-so-ever, either the 8302 is not managing the COMMS Clk and COMMS Data/out lines properly, or else one or more of the pair (PNP and NPN) of transistors that form the power drive cct on each MDV (as installed on the QL main board) are faulty.
That 9v rail should be working OK if the rest of the board is up and, even if it was below spec, the LED/Motor should start to light-up/ spin.
That said, if the 500mA linear regulator is dead on either MDV head-board, then the respective MDV ULAs might not be driving the COMMS Out signal which then drives both the power cct for its own drive, plus the next MDV's COMMS In, so as mentioned below, swapping over MDV2 for MDV1 would be a useful check. In so doing, you'd also get a good look at the inter-board connectors that join to the MDV head-board.
Along with the lack of beeper, a curious combination of errors indeed!
I have an 8302 and spare speaker on their way to help me test. I will then try swapping over the mdv units.
All chips have been reseated
The previous owner said he was getting a white screen on start up - I did get that briefly, but then after a reset, it came up with the F1/F2 screen (and now does so every time, even starting from cold).