A4000 ownership not going well

[Higgy]

Hi,

Well I got about 1min out of her before she died

I was told it was stable but with battery damage. I got purple Kickstart screen, popped in a disk, booted to Workbench to try AmigaTestKit then it froze. I turned off and on and now I just have Black Screen. TV seems to recognise some signal but no Kickstart appears.

I have changed caps (no damage) there were 3 broken traces due to battery damage near C192. 2 for HDD LED and 1 for R_W_ (memory?).
Capacitor C192 came away with pads, it seems a PSU smoothing cap, I did try soldering another using the 5v and GND via's just to the right.

Traces seem good coming from chips near where the battery was.

Diagrom gives White Screen. Take out Processor Card (030EC) and just get Black Screen.

Any ideas what to try or maybe a 4000 repair expert to recommend? Some chips get normal warm, others stay cold.

Cheers

[Steve]

I am by no means an Amiga expert, but I have fixed about 4x different Amigas in my time, each time I used: https://www.amigapcb.org/

I would start around the battery damage, use that website and check with a multi meter all traces to various components. I then would remove all socketed chips - clean all chips and chip holders, replace.

[Higgy]

@Steve thanks for the link, yes that is a good website.

I am running out of ideas, I was wondering if it something to do with the Reset circuit. One website said it will still boot with some RTC related chips removed. But they can cause Reset issues.
One is right next to the battery, I took that off and it was clean underneath. The other is the Ricoh RTC but it's a thru hole and I could not remove.
It's further away and tracks are ok with a multimeter so I doubt there is corrosion issues there. I don't really want to snip the pins.

Ok this PCB there are only 3 socketed chips, Kickstart and another nearby, the complete other side of the PCB from the battery.

[Steve]

@Higgy don't be snippin anythin! lol Just get your multi-meter out and start buzzing out all the connections around the battery damage using that website as your guide.

[Danoo]

Have you had a look at Chucky's handy hints http://wordpress.hertell.nu/?page_id=218?

Directly from his website; "Like SCLK generated by LISA (pin 22). if SCLK is not generated it might be U975 that is faulty as it generates MDAT that is required for LISA. os if MDAT is low, no SCLK will be generated meaning no boot. U975 is often affected by batteryleakage.".

I have had 2 dead A4000's with a fault in this area, one was just a bad via just outside of the battery leakage area and another with a corroded joint on U975, so probably worth tracing these tracks with a continuity tester and Amiga PCB explorer https://www.amigapcb.org/

[Higgy]

Update.
I thought everything was ok, it would boot to Workbench and run Workbench stuff ok. Sometimes Fastram would not be detected and some WHDLoad games/demos would just give a black screen when they previously worked. I thought it was poor connections around U891.

But then it stopped booting and seemed to get stuck in a bootloop/reset cycle. Typically it had to be after the case was reassembled!

It would boot into Diagrom fine but with Kickstart ROMS no go.

I changed U975, U976 and U177 even though battery leakage is good there (I think computer was stored on its side so did not travel there).
I also changed U891 (worse leakage).

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.

I soldered a socket to U178 and when I fit the original RTC (got no replacement yet) it goes back to bootlooping/reset cycle. So hopefully that explains that, and it seems like memory addresses go through the RTC so I am hoping that explains why I only see 1mb per slot.

Looks like the RTC is quite critical to the 4000 operating correctly. Fingers crossed a new Ricoh RP5C01 will fix it. Then it will be back to stability testing. Need it to work for the TF4060

[Danoo]

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.

You have probably already checked this, but just in case you have not, have a look at J852 it sets the SIMM type for the fast RAM slots (position 1-2 4MB SIMMS, position 2-3 1MB SIMMs). The jumper is just above the SIMM slots on a RevB.

J852 position

J852.JPG (50.66 KiB) Viewed 4628 times

[dalek]

traces and vias under the simm socket closet to the battery can also get taken out with battery damage. Worth buzzing them out against the PCB layout at the above mentioned amigapcb.org

[Higgy]

@Danoo thanks for mentioning. I've not touched that Jumper but it was worth checking. I did notice it is for either 256kb or 1mb chips. My Fastram modules are 4mb with 8 chips so 512k each, but when it did work it would detect the correct amount of ram in each slot.

@dalek there was one that goes to the Chip ram I had to repair. Others seem ok. Visible damage was mainly focused around bottom row of U891 and C192.

I am hoping now it is just down to no RTC chip being fitted as Address lines pass through it. Hopefully have some replacements in a week or so.

CIA B has always shown a fault. Now CIA A is showing same tick fault, again wondering if due to no RTC chip now being fitted. Mouse, and Keyboard work. RTC chip has lots of links to the system.

[Higgy]

RTC chip arrived by still only 1mb of Fastram per slot.
I spent 1.5 hrs last night tracing all around Fastmem.

Maybe she is just destined for e waste...

I was wondering that with a TF4060 then that should just bypass the Fastram issues as memory will be on the CPU slot.

I've got some ATX PSU conversation parts turning up to try as a last straw.