A4000 ownership not going well

[Danoo]

E-waste, :o :o :o, if you can not get it going correctly, maybe a friendly local U-Tuber may have a go at fixing it in a video :).

[Higgy]

I might even consider paying for them to migrate the chips to a new PCB. Good for their views - a new 4000 build.
Now, just need to find a skilled 4000 expert that is good with Gadgets who has his own YouTube channel... :D

[PhilC]

I might even consider paying for them to migrate the chips to a new PCB. Good for their views - a new 4000 build.
Now, just need to find a skilled 4000 expert that is good with Gadgets who has his own YouTube channel... :D

Now that's a difficult one. If only the clue was in the name :D

[Higgy]

Damage is mainly localised to C192 and one side of U891.
The 3 traces below C192 were gone and acid crept down those VIAs (2 for HDD light 1 memory trace).

U177 area and lower resistor pack looks fine.

Caps also looked ok on the board, no obvious corrosion. They have been changed. CPU cards ones still original and 4000 was run with 060 card so the 030 card I have has probably been unpowered (until my recent ownership) longer than the overall 4000, which again has been in storage.

I've changed U177, U975, U976, U178 and U891 and chopped and changed back and forward with the originals through desperation.

It looks to me that even if the lower SIMM was mashed apart from that 1 trace (that has been repaired) the signals come from further up the PCB as the Fastram connections are dasychained.

Maybe there is a way of testing what memory addresses it can detect to narrow down the issue?

IMG_20221012_110530.jpg

[Maximilian]

I removed the RTC IC U178 and it now boots but only 1mb of Fastram per slot is detected. I also tried the original U891 back in (current state) but still just 1mb detected per slot.

Sounds a bit like:
https://www.tsb.space/knowledge-base/a4 ... g-atx-psu/

[Higgy]

@Maximilian ah yes, this is what is leading me to make an adaptor to use a ATX PSU.
I am not sure how to test if my original PSU is sending out the correct signal?
I am sure I traced the PCB signal from the PSU connector to where it needs go. Will test again.

On EAB there was someone with the same fault some years back, apparently it was quick and easy for the fixer. But the fixer would not share what they did!

I also see 4000's with a diode connected to a pin on the RTC. But I think this is more boot related. My 4000 seems to at least boot everytime.

[Higgy]

I got the new RTC, so that is fitted in a socket. Some of the values on the 10K ohm resistor back below the RTC were a bit low so it have replaced that.
I have also put on a new U891.

Still waiting for the ATX extension, I've got the Amiga Power Connector through.

I got a logic probe and there is a signal coming from the PSU _FAIL / Power_On.
I also see pulsing from U891 when doing memory tests.

I found some 8mb modules. If I put them in Slots 1 & 3 it registers 1mb per slot.
If I put them in Slots 2 and 4 they register 2mb per slot?

[stephen_usher]

Sounds like you have address line problems to the sockets.

P.S.
Forget that.... Looking at the schematic, it's more likely to be the CAS lines as that will be selecting the "banks" of RAM in the SIMMs.

P.P.S.
Check the continuity of the CAS and RAS lines on the SIMM sockets. Sounds like you have track damage under there... (PCB explorer is very useful here: https://www.amigapcb.org/)

A4000-CAS-RAS-Lines.jpg

[Higgy]

@Maximilian well I made up my ATX adaptor yesterday...... And the memory is back!?! :)

@stephen_usher thanks for that, I followed that and tracks seemed good so the PSU was really the only thing left to try.

I now have 2 faults on both CIA's (TOC tick). It was just on CIA-B then CIA-A developed a fault. I noticed with my testing yesterday pressing some keys on the keyboard Up/Down cursor sends it mad and using the PCB Explorer a Keyboard signal goes to Pin 43 on CIA-B.

I am thinking of placing those chips in a PLCC socket. Need to investigate if I can achieve that. Thankfully Ramsey seems alright and does not need replacement/socketing.

Hopefully that is the main issue sorted. I need to keep running the system and check it does not loose the RAM again.
I need to think about the PSU. Either transplant the new ATX guts into the old PSU case to keep the Power Switch or do something else temporarily.

[stephen_usher]

:dualthumbup: