Faulty RAM or 8301

[Chris_68]

Hello all!

I'm afraid I need some guidance and help, I had a working QL..
Installed a memory upgrade and Minerva indicated a RAM failure in the expanded RAM, after some trials I decided to remove the expansion. I was really careful but managed to ruin the red CPU socket. Unsoldered pin by pin and placed a new socket.
I put back the expansion board but still got RAM error, removed expansion board but the QL started to behave more and more weird. Can post a video tomorrow, right now the screen is black.

IC19 and IC20 seems to be fine, not very nice signals on pin 4,7,9,12 (74LS257) but something. On IC21(74LS245) I don't get anything on B0-B7 which I guess I should?
If I like to measure 8301, should there be a signal on pin30-32? I'm using RGBtoHDMI
I have minerva ROM, is it possible to read data from it without unsolder from PCB?

Thank you for any input and help.
Chris
QL PCB is a ISS7

[Pr0f]

What are you using to measure your signals?

[Chr$]

Is it the RAM board from me? If so it's probably a good idea to check the traces on it (I can send you a list of where everything goes to ping out) as they can be a bit fragile of they are remove/re-inserted multiple times.

But you say the QL is behaving funny even without the extra RAM, so I suppose you need to sort that first!

The ROM board (if it's the one I'm thinking of) is mostly straight through to the same pins in the socket, apart from pins 1, 20 and 22.

[Chris_68]

What are you using to measure your signals?

Hi Pr0f,

Thanks
I have oscilloscopes, multimeters LCR meters so pretty well equipped.
/Chris

[Chris_68]

Hi Chr$

Thank you and others for help and input.

Is it the RAM board from me? If so it's probably a good idea to check the traces on it (I can send you a list of where everything goes to ping out) as they can be a bit fragile of they are remove/re-inserted multiple times.

Thanks, Can come handy, first I have to sort out what's causing the problems in standard setup though.

The ROM board (if it's the one I'm thinking of) is mostly straight through to the same pins in the socket, apart from pins 1, 20 and 22.

It's the "common" one. I have to check what those pins are, I think CE/WE. I might be wrong but then its not possible to read the contents with a programmer without removing the chip? Just like to verify the ROM is ok.

Regarding the IC21(74LS245), I will remeasure again, are pin 11-18 (B0-B7) output to memory and 8301. There's nothing on these pins, with voltage on pin 1 there should be right.

regards
Chris

[Pr0f]

So testing the R,G and B pins with a scope is not a bad shout, and test the synch signals (can't remember which pins), but see if the ZX8301 is at least producing a video signal.

If I recall Chr$'s RAM board - is that an internal one using a 512K SRAM ? If so - it's likely not going to affect the on board RAM.

There are a few places where things can go wrong:

The 257 Mux chips - these multiplex the QL's address bus to the on board RAM - they won't stop the ZX8301 outputting some sort of video though - unless the outputs are somehow 'held' on and thus holding RAM address lines and preventing sensible data getting to the ZX8301 to produce video

The 245 chip is the bus transceiver - similar role to the above chips - but this time it's concerned with the data bus only - again - if it's always outputting you'll get contention.

The ZX8301 chip - these are known for failing - usually down to plugging in anything into the QL video socket particularly when things are on. The Video outputs are not protected and the chip can suffer failures as a result of static or odd voltages going back into the chip - if you do have a spare one - a simple swap is a good way to diagnose

The Clock - sounds obvious - but the ZX8301 takes in the 15MHz signal from the crystal, and outputs the 7.5MHz CPU clock - you can validate these signals with the scope - at least you will know there is a heartbeat then.

The Processor - If you have had to remove and replug the processor - check for bent pins, solder bridges between pins on the socket or lifted tracks (some of them are small), on both top and bottom of board.

[Chr$]

It's the "common" one. I have to check what those pins are, I think CE/WE. I might be wrong but then its not possible to read the contents with a programmer without removing the chip? Just like to verify the ROM is ok.

Yes, sorry, for some reason I thought you meant reading (scoping) signals from it. That would indeed be difficult. I can lend you another one.

[Martin_Head]

The Processor - If you have had to remove and replug the processor - check for bent pins, solder bridges between pins on the socket or lifted tracks (some of them are small), on both top and bottom of board.

Also if you any trouble getting the old processor socket out, you might have damaged the through plating in the holes.

[Chris_68]

So testing the R,G and B pins with a scope is not a bad shout, and test the synch signals (can't remember which pins), but see if the ZX8301 is at least producing a video signal.

If I recall Chr$'s RAM board - is that an internal one using a 512K SRAM ? If so - it's likely not going to affect the on board RAM.

There are a few places where things can go wrong:

The 257 Mux chips - these multiplex the QL's address bus to the on board RAM - they won't stop the ZX8301 outputting some sort of video though - unless the outputs are somehow 'held' on and thus holding RAM address lines and preventing sensible data getting to the ZX8301 to produce video

The 245 chip is the bus transceiver - similar role to the above chips - but this time it's concerned with the data bus only - again - if it's always outputting you'll get contention.

The ZX8301 chip - these are known for failing - usually down to plugging in anything into the QL video socket particularly when things are on. The Video outputs are not protected and the chip can suffer failures as a result of static or odd voltages going back into the chip - if you do have a spare one - a simple swap is a good way to diagnose

The Clock - sounds obvious - but the ZX8301 takes in the 15MHz signal from the crystal, and outputs the 7.5MHz CPU clock - you can validate these signals with the scope - at least you will know there is a heartbeat then.

The Processor - If you have had to remove and replug the processor - check for bent pins, solder bridges between pins on the socket or lifted tracks (some of them are small), on both top and bottom of board.

Thank you!
there's an output from 257 on pin 4,7,9 and 12 so I leave those for now,
245 had DC on B0-B7 but no signal so replaced that one but still the same symtom and dc on output...
The RAM chips have a signal, will remeasure and document better.

I will measure on 8301 again and report back, could be something there, wasn't any proper signal. While fiddling around trying to find the RAM problem I realised the RGB cable was a bit loose....

CPU, well it could be something after the soldering, I know I got a solder bridge on the small external port but couldn't see anything wrong near CPU. Will do another check.

Thanks again

[Chris_68]

It's the "common" one. I have to check what those pins are, I think CE/WE. I might be wrong but then its not possible to read the contents with a programmer without removing the chip? Just like to verify the ROM is ok.

Yes, sorry, for some reason I thought you meant reading (scoping) signals from it. That would indeed be difficult. I can lend you another one.

Hi,

Very kind of you, I don't know why it should be the ROM, just desperate I think, don't want to mess upp more by delsodering the ROM so was hoping to read data from it.
I have C128,C256 and C512 so could try and program those. Which ROM and EPROM version/combination will be the best to try out?