Piggyback 4164 to Diagnose Memory Fault

[t0nyt]

I have a bare PCB and can take a photo later.

I still suspect the logic circuitry, since it’s random, which one is it you replaced?

The larger 20 pin one nearest the ROM sockets (SN74LS245N)

The Minerva error codes, since fitting the logic IC & IC8, are the same every time I switch on and I don't get the black & white lines any more

I did piggyback the other 2 logic IC's as my theory was that if one of the onboard logic IC's were faulty the combination of a piggybacked logic IC would cause random things to occur, but everything remained consistent which suggested to me the onboard and piggyback were working identically. But I know nothing about this so that is very much pseudo science!

Thanks
Tony

[Chris_68]

Hi,

Here's two photos, I will double check exactly which IC it is.

Maybe you have written it before, but do you have solder flux and wick? Clean up where you replaced the ICs and if possible send a new photo.

For me the 245 and 257 gave very noisy and if I remember correctly output signal even when there were no input so if it's the same problem with yours I doubt it helps to piggy back.

[t0nyt]

Hi Chris,

Sorry, I thought it was going to be a photo of the IC11, but that seems to be something else?

Thanks
Tony

[Chris_68]

I thought it was IC8 you had problem with now, sorry. A new photo in bit

[t0nyt]

I thought it was IC8 you had problem with now, sorry. A new photo in bit

Sorry, my fault. As far as I can tell from photo I took before I changed IC8 it seems ok (even though it's the one generating the fault)

Am looking to double-check IC11 as it's where I made such a mess

Will use your photo to double-check IC8 though too, thanks

Thanks
Tony

[Chris_68]

Hi

This is IC11

Double check so you the track around pin11 is alright,

[Chris_68]

BTW is yours issue 5?

[t0nyt]

BTW is yours issue 5?

Yes, Issue 5

Thanks for the Photos

I can't see anything different between yours and mine on IC11 (or IC8) in the sense of tracks etc, and I've tested the whole area for shorts and breaks

I guess I'll have to try and change the other 2 logic IC's, but I guess the problems could be on the top of the board under the sockets in which case I won't get anywhere as I can't face going back and removing them

Many thanks
Tony

[Chris_68]

Hi

Replace the two remaining ones, even if you didn't find any problem with multimeter I would clean around IC11 and make sure you don't have any cold joints.

[Martin_Head]

I don't know if these pictures of bare boards will be of any help viewtopic.php?p=24839#p24839

If you blow them up, you can just about follow the tracks.