CPU not starting

[dfzx]

Sorry to stick by rather uninformed oar in again, but...

Are you not measuring variable voltages (i.e. AC) with a digital multimeter and trying to interpret the results as DC?

If I have, say, a 3.5MHz clock signal, which swings from 0V to +5V on a duty cycle of 50%, what would I expect to see if if measured that as a DC value? I sort of assumed 2.5V, but I guess it depends on the meter?

[1024MAK]

In the last set of tests, the ULA is not fitted, hence there is no AC signal, the circuit is only operating in a static / DC state. This is primarily to confirm that in a static state it is working okay. It's much easier to pick up basic faults in a static state.

As to what a digital meter will show when testing a 3.5MHz signal, that is unfortunately an unknown, as the bandwidth and sampling system for the meter comes into the equation. Hence I try to avoid this kind of testing.

Mark

[dfzx]

In the last set of tests, the ULA is not fitted, hence there is no AC signal, the circuit is only operating in a static / DC state. This is primarily to confirm that in a static state it is working okay. It's much easier to pick up basic faults in a static state.

Oh yes, of course, that's why the ULA had to be removed.

[Brendan1495]

Hi All,

I would like to thank you for all your help its all working now. I have got to admit I feel a bit a knob head admitting this but there nothing wrong with the clock circuit, I has spent a week trying to diagnose the problem and tonight after doing a few more tests it noticed the ULA didnt seem to be making a good connection, I removed the socket and discovered 2 bent pins so 2 pins were not making a connection, resoldered a new socket, put in the ULA and it booted up straight away.

Like I said thank you all for your help and assistance in trying to fix my stupid mistake.

Brendan

[1024MAK]

Thank you for reporting back

Glad that you have found the problem and now have a working board

And it’s good to confess mistakes. It allows other members to learn. You are not the first and will not be the last to suffer from bent pins...

Mark

[MustardTiger]

Were the bent pins on the ULA or the socket? How were they not making a connection? the pins to the socket or the socket to the board?

[Brendan1495]

Were the bent pins on the ULA or the socket? How were they not making a connection? the pins to the socket or the socket to the board?

Bent on the Socket, socket to board

[Brendan1495]

Were the bent pins on the ULA or the socket? How were they not making a connection? the pins to the socket or the socket to the board?

Have you tried replacing the lower ram board with chips, I have to admit I couldn't get the board to work (Same one as yours) just an idea and probably wrong as I am a noob at repairing these things but getting better with the advice from the guys on the forum.

Brendan

[MustardTiger]

Have you tried replacing the lower ram board with chips, I have to admit I couldn't get the board to work (Same one as yours) just an idea and probably wrong as I am a noob at repairing these things but getting better with the advice from the guys on the forum.

Brendan

I haven't but it's something I considered but I'd have to sink even more money into it. Currently I can't test any fixes as I don't have a ULA and I'm not prepared to buy another unless I find a definite fault with a component. I'm about to do the DC-DC mod fix and replace the power transistors to try get the +12v line working correctly. I hadn't focused on this before because the ram board doesn't use the 12v.
Seeing that your fix wasn't a problem with the clock filter made me realise that my fault is probably not the filter either. I'd been too focused on it before.