Struggling to resurrect my +2 :-(

[zxplusplus]

also, if thermal expansion is the culprit, am I correct in saying that I could check all the traces on a cold board and still not find any faults!

[Ast A. Moore]

also, if thermal expansion is the culprit, am I correct in saying that I could check all the traces on a cold board and still not find any faults!

Use a good light source and a magnifying glass. Rotate the board to change the angle the light falls on it. You might still need to remove the IC sockets and inspected the vias underneath them. Reflowing all the joints with fresh solder will also help.

I’d start the inspection with the CPU socket/vias.

[1024MAK]

also, if thermal expansion is the culprit, am I correct in saying that I could check all the traces on a cold board and still not find any faults!

This is possible, yes. But often the resistance of a poor connection is higher than a unbroken and good track / conductor/ connection.

If continuity testing does not show up a problem, then the next step is to use the multimeter (on resistance) to look for short circuits / leakage paths.

If the fault then continues to be elusive, either heating (hot air) or cooling (freezer spray) different areas may help.

Then if an oscilloscope was available, it would be possible to compare signals, looking for any significant differences. In the absence of a ‘scope, a logic probe or a logic analyser can tell you the logic level of a signal and can also be valuable tools.

Mark

[zxplusplus]

Thanks both

I've ordered new sockets for the CPU and ROM, I'll replace both to firstly make sure there are no dry joints or other damage.

I'll then start working my way round the traces, starting with the CPU and ROM.

My multimeter has a continuity mode which should help

[zxplusplus]

quick update

I printed off the schematics and zoomed in on the CPU, ROM, PCF1306p area. I then worked through all of the connections between these chips (using the leg of the chips), all connections are fine on a cold board.

I'll run it for 20 mins or so and then do the same thing again..

[1024MAK]

quick update

I printed off the schematics and zoomed in on the CPU, ROM, PCF1306p area. I then worked through all of the connections between these chips (using the leg of the chips), all connections are fine on a cold board.

I'll run it for 20 mins or so and then do the same thing again..

As well as the PCF1306p (IC10), also include the connections between the Z80, ROM and the main ULA (IC14).

Mark