Help with Apricot-Pc video and disk drive issue.

[roadrash]

I have a couple of vintage Apricot Pc's that I have got to work after rebuilding their PSU's which as usual blew the Rifa filter caps etc. One of them was working great and the display output on its tiny dedicated green screen monitor nice and sharp. After a while I noticed that it had got some interference on the display which is not the fault of the monitor as it tests fine on the other Apricot that's working and swapping PSU's over makes no differnce. So it must be a component failing on the motherboard. The other Apricot has a good display output but wont read properly from any of the known good disk drives. I have not yet recapped the motherboards and this will be my next job now I know its not a monitor or faulty disk drive.
Is there anything in particular other than the caps, I should be paying attention to re the video & disk drive issue on these motherboards?
Pictures attached.

[R_J]

Re: Help with Apricot-Pc video and disk drive issue.

The first cap I would suspect for the video problem would be C3 100uf located on the base of TR1 (next to the video connector) Then I would change the caps off the PSU Connector CM, CE

[roadrash]

Re: Help with Apricot-Pc video and disk drive issue.

I have replaced some of the caps one one of the apricots including the ones you mentioned and after giving it a test, the video output is still messed up but now the disk drives which were working are no longer reading disks although are are seeking.
I have been trying to check each caps connection one a a time using the other untouched board as a guide. Its proving very time consuming as its obviously a multilayer pcb as some of the solder joints don't go to any tracks and just appear to go nowhere. I have managed to trace these and found them connecting to a component nearby which proves they are connecting via a track hidden inside the pcb. There are some that after much time now, I cannot trace where they are going to and without a schematic (there are none anywhere) its near on impossible.
obviously one of the caps I replaced is not connecting properly as surely using a 16v cap instead of a 10v cap wouldn't affect the disk drive reading would it.
Ive still yet to cure the video issue as well.

[R_J]

Re: Help with Apricot-Pc video and disk drive issue.

Is'nt this the manual with schematic for that model? have a close look at the leads of the capacitors you removed and see if any of the feed-thru's came out with the cap. on a multilayerboard like these it may be better to cut the leads at the cap body and attach the new cap to the original leads.

[roadrash]

Re: Help with Apricot-Pc video and disk drive issue.

Thanks for that info. Did eventually trace where all those caps connected to and obviously they all have a connection. So thats makes me wonder why the disk drive is no longer reading a floppy if all I have done is change these caps for the same capacitance value except they are 16v and not 10v. Surely this wouldn't cause this would it?. Nice tip on removing those caps. They actually came out easy and didn't pull the feed thru's out. I know what you mean though, ive done that before when a components a tight fit coming out.

nice hand written schematic.

[R_J]

Re: Help with Apricot-Pc video and disk drive issue.

I have no idea what happened to the drive not reading, uping the cap voltage will not make any difference. does it give a drive error code? not spin? seek but not finding the media?

[roadrash]

Re: Help with Apricot-Pc video and disk drive issue.

Not sure myself why it should stop reading the disk. When its turned on the display comes on and the disk drive moves its head across the disk surface as normal but then doesn't start reading and booting the disk as it used to do before I changed the caps. If its not a voltage issue with those caps all I can do is follow the schematic cap by cap that I replaced and check they are all connecting to all the right places.. cheers thanks

[roadrash]

Re: Help with Apricot-Pc video and disk drive issue.

OMG, what a schematic! I am no expert but this schematic is hard to follow and doesn't show all the electro caps there are and its very hard to follow.
Caps don't have a unique ID and 4 or more caps having the same ID and can located close by as well as well as other area's all over the pcb. For example there are 4 caps near the 8x4 rows of memory chips all with the ID of "CE" (3 coloured grey & one black all 68uf 10v) and are not even shown on the schematic anywhere near the ram chips but there are other caps marked as CE in other areas as well. This is proving a real challenge and will need some help here.

[roadrash]

Re: Help with Apricot-Pc video and disk drive issue.

looks like i may have found the fault. I removed all the caps i put in and desoldeted and checked all the contact pads and one susicious looking one when viewed under a magnifying glass revealed what you see in the attached picture. I couldnt belielve how close that track was to the pad and remember that pic is magnified. its litterally only about .2 mm away. I think its best to tun a link wire across instead of repairing and reusing that track

[R_J]

Re: Help with Apricot-Pc video and disk drive issue.

It looks like the line is the DCDB (data carrier detect B) between the z80 pin 22 to ic6 pin 16 I did't trace it any further but it may have told the system to look at connector C instead of the ide drive, just a guess,
IC6 driver chip for controling inputs/outputs/ on Centronics parallel port.
running a thin wire between the 2 points should be fine.

[roadrash]

Re: Help with Apricot-Pc video and disk drive issue.

that makes perfect sense and now hopefuly the disk dtive wil read disks again now