The Sinclair QL Forum

Nice step forward.

Please, write down what you have done of advises or what not yet. In order to know how is going on the real state.
Otherwise we are not synchronized.

Just checked IC21 on the A side I am getting this.
https://youtube.com/shorts/Jo_yYMqE690?si=1ZEYW0wfYpTOwIbr
And on the B side I am getting this
https://youtube.com/shorts/1tZc5g3p2wQ?si=xRoPIPWu6W-mENJz


On Side B this happen to each line?

So, everything that works on side A (CPU, etc) works ...

Re-reading the thread but didn't find this...
have you remove the ICs from the sockets, cleaned the sockets and also the pins from each IC and re-seat them?

That is also basic & easy to do, and could produce what you are suffering.
Since you have activity, it may be related with bad IC connections ...

Hi
Forget what I said about the VCC voltage as the pinout I was following although it said it was the right chip was wrong so now have rechecked and voltage is fine and DOut and address lines showing activity. IMG_20250710_123608_edit_44377249836977.jpg


If I am not wrong (my eyes are ...

I have tested the ram chips DOut and the address lines A0 to A6 all showing activity but checked the VCC of each chip and it's showing 2.68v is this correct.


As far as I know, no.
That is not correct.
Those chips must be feed by +5v

I share a schema of one QL version in case it may guide to to ...

Hi
Tested the cpu the voltage is 4.91v the clock signal is showing this. IMG_20250710_100416_edit_41840307230913.jpg
With the reset it is showing this.
https://youtube.com/shorts/ag-cjybbV9M?si=DeN5qw4JgIvzISPY


Beautiful oscilloscope, I love it.
So the main rail of +5v is working fine & not ...

Hi,
There are some basis things to test first at all when getting a new old computer.
1. Power voltages from power supply.
2. Shorts in main board between power lines and GND
3. Measure of the power regulators inside the computer, in this case in QL the main one is the +5v from the linear regulator ...

A full memory test requires to:
1. Detect shorts
2. Fill the whole memory with at least 4 different basic patterns and read them are the same after it. "00", "11", "01", "10" and random. What takes some time.
3. In case of DRAM ICs, also check after a while the data remains (refresh).
4. If ...

I removed the soldered IC3 and replaced it with a socket. The chip tests as OK in my Retro chiptester pro! But it clearly isn't, or it's at least marginal in some respect.

And with a known working 4164 in the IC3 socket everything is fine.


Have you considered the idea that perhaps the problems ...

...
Unfortunately, with just the dodgy IC3 in place on its own, the Diagrom completed its tests and reported no issue. I'm not complaining of course, because as you say, the diagrom is just one tool is the diagnostic arsenal and whatever issue there is with IC3, it seems an unusual one.


It's a ...