Dead A3000

[Vypr]

I've managed to score myself an Amiga 3000 from eBay and am hoping to get it fixed up so looking for some pointers on what to check.

Symptoms

Power LED comes on but stays dim. Caps lock light toggles on and off six times then stays off. No video signal on either RGB or VGA.

State of the board

• Varta battery had been replaced with another Varta,. There is very little corrosion, a tiny 5mm diameter patch can be seen around the Ground pin which has been neutralized and cleaned. Traces in the vicinity of the battery have been checked for continuity.
• Minor corrosion present in the Paula socket.
• All the PLCC sockets had damage and the chip surfaces have scratches, looks like the previous owner tried to remove some of the chips with a screwdriver, all the PLCC sockets came apart when the chips were removed.
• All the ZIP sockets are populated as was were the FastMem DIL sockets.
• Kickstart 3.1 ROMs in place

Troubleshotoing performed

• Varta battery removed, I don't trust them, I will be replacing this with a coin cell holder at some point.
• Plugged a terminated SCSI cable in.
• Removed the FastMEM DIP chips as I understand the 3000 is supposed to work in either/or for the DIP and ZIP memory
• All the PLCC sockets have been replaced
• Paula socket replaced
• Tested with DiagROMs in place.
• Swapped Denise and Agnus with known working chips
• Plugged in an A3630 card from my A4000
• PSU voltages tested OK
• Board checked for dry solder joints.

After all this the issue remains the same, the power LED remains dim, there is no video signal on either RGB or VGA.

My next step will be to replace the 28Mhz clock chip as I have a spare to hand but any pointers on what else to check would be appreciated.

[cpiac64]

first check 5 volt and reset

[Vypr]

Originally Posted by cpiac64

first check 5 volt and reset

5V is present and correct, trying to find in the schematics where the reset line is.

Have managed to get a video signal by replacing the socket for the RTC but still getting a dim LED

[cpiac64]

long time ago i have repaired one, trace broken under U480

[Vypr]

I'm only seeing 0.16V on the RESET line output from U713

[alexh]

Someone just recently had an A3000 with the Kickstart ROM chips in the wrong sockets. The higher U number is the lower half of the ROM I believe. If in doubt swap them round

[Vypr]

Originally Posted by alexh

Someone just recently had an A3000 with the Kickstart ROM chips in the wrong sockets. The higher U number is the lower half of the ROM I believe. If in doubt swap them round

That occurred to me as well so I did try swapping the ROMs around but getting nothing. I was getting an RGB signal before but when I started probing the RESET line I suddenly lost that as well, May have accidentally shorted something with the probe.

[Vypr]

OK, found the short, the CPU looks like it had been hit by something prior to when I got it as some of the pins were bent, one of the pins was off its pad and shoritng to the adjacent one. Managed to nudge it back into place with a soldering iron and the RGB signal is back. I've gone ahead and replaced the CIA and SCSI sockets as they were a bit crusty, it took a lot of force to get the CIA chips out of their sockets, reseated and checked all the remaining sockets and they all seem good, all the contacts are nice and shiny.
The CPU gets very hot but I'm not sure if that's normal or not but I woul d have thought that inserting the 3630 CPU card would bypass the onboard CPU.

[hooverphonique]

Did you fix the reset line? If it's floating, it can cause excessive power consumption in the input circuitry of chips relying on this signal. Also, your computer won't work properly.

[Vypr]

Reset line is stuck at 0.16V

Also it looks like something may have hit the CPU as I found some more of the pins are bent. .

I again gave it a gentle nudge with the hot soldering iron but the pad started to lift o I'm leaving that alone.

[Vypr]

OK, so I;ve done some more checking. I;ve found that the resistor array at RP701 is looking suspicious.
According to the schematic, RP701 is a 470 Ohm array with pin 1 connected to 5V. Measuring resistance across the pins shows 470 Ohms on all the pins except pin 4 which is on the reset line, the resistance here is measuring 330 Ohms, could this be my culprit?

[hooverphonique]

Originally Posted by Vypr

According to the schematic, RP701 is a 470 Ohm array with pin 1 connected to 5V. Measuring resistance across the pins shows 470 Ohms on all the pins except pin 4 which is on the reset line, the resistance here is measuring 330 Ohms, could this be my culprit?

The resistor is probably ok, but in parallel with something else that provides a similar resistance relative to +5V. I suspect you either have a direct short to GND somewhere, or a component is pulling reset low.

[cpiac64]

remove all chip connected to reset and power on for verify if reset is 5volt or not

[Vypr]

Originally Posted by cpiac64

remove all chip connected to reset and power on for verify if reset is 5volt or not

I can see 5v going into RP701 which feeds the reset so if that resistor pack is fine then something else is holding the line down. My suspicion is with the processor itself as every so often I lose video signal until I nudge those bent pins. If I were to remove the 68030 would it work with the 3630 card? I took that card out of a working A4000D and replaced it with a 3660 so it's going spare.

[r.cade]

You will have to fix the shorts, which means correct the bent pins/crossed pads, or else remove the CPU, clean it up, and put it (or a replacement) back. I am not positive the 3630 will work on the A3000 (especially with no CPU installed) but I would think it should.

[Vypr]

So I've removed the 68030 and cleaned the pads but I'm still getting a short somewhere I'm reading only 85 Ohm resistance from 5V to GND which indicates to me a problem somewhere

[cpiac64]

sometime a ceramic cap go to short, but if 5 volt are ok, continue investigation

[Vypr]

Think I might have foudn the culprit. The 7407 hex buffer at U713 doesn't seem to be passing signals from pIn 5 to 6. tested it with a logic pulser and it remains presents a low voltage which I believe is taken as a logicla High signal despite what is presented to Pin 5.
Tried to check the chip out of circuit by putting it ona breadboard but managed to blow the fuse on the PSU by shorting 12V to GND. Fortunately the PSU wasn't connected to anything else so hopefully it was just the fuse that blew.

[Vypr]

Have now replaced the PSU with an ATX supply, socketed and replaced U712 & U713 but still nothing.

_RESET and _CPURST are always at 0.16V
So far I have tested with known good Agnus, 68030 and 68060 processor cards. I have replaced the all logic circuits on _RESET and _CPURST and still nothing.

Denise and Amber should be OK as I am getting a video signal on both RGB and VGA and I tested the Super Buster on my A4000. My only remaining suspects are Fat Gary, Super DMAC and Ramsey. I have sourced replacements for Gary and Ramsey and will try them when they arrive. Is there anything else I can check?

[Vypr]

I have made progress!
The _FAIL line was showing 2V which was stopping Fat Gary and Ramsy from initializing. If I remove the RTC chip it shows a steady 5V and I can now see the _RESET line going from Low to High on a cold boot. I'm still only getting a black screen but DiagROM gives em a single character on the serial output so something is happening.
I have also noted that one of the legs on C411 has broken off from the end of the cap I'm not sure if this will affect the boot sequenceas this just feeds off to the daughterboard.