Need help fixing A4000

[magnetic]

Jumpers factory default, try with an A3400 68030 w or wout copro .
Maybe problem is in cpu card or slot
hope this help you

We wouldnt need to guess if the CPU is good or not if he does the CAPS LOCK trick I said earlier. This determines if the cpu is the problem or not.

[Mr_Vanos]

Agreed, that would be incredibly helpful in the right situation.  Unfortunately the UART (the bit that makes the serial port work) lives in Paula.  And for Paula to work, it first needs valid clocks that are divided and generated by both Alice and Lisa, so the bulk of the video sub-system needs to be working.  And Paula lives on the other half of the Amiga sub-system on the chip memory bus side.  And to talk to that, the data bridge needs to be completely working in both directions (Bridgette in the A4000).  And to talk to that, the address decoder (Gary) needs to be working.  And to talk to that, the entire CPU subsystem needs to be working.  And... hey that's most of the computer already.

Well, my idea would be to bypass most of those components. If you could use just a timer and GPIO in a CIA, you could twiddle some pins on the CIA, and perhaps even bit bang a serial interface with a clip on RS-232 line driver.

The other way is to replace various bits with known good bits - also known as the 'shotgun' approach.  The problems there are that you need a source of known good bits, and you need to make sure all of your soldering work is 100% else you'll introduce new problems which simply compond with the original one.  Also, this doesn't help at all in finding PCB related faults, which are fortunately rare except in case of battery and capacitor corrosion - unfortunately which are common in the A4000.

That is a bit of a problem as I don't have a lot of known good spares. The CIAs I have are brand new, the mouse is brand new, but I don't have an Amiga branded keyboard (the northgate one does work on a PC in PC mode), no extra CPU card. I have an A1200 board that I could steal an Alice and I guess Lisa, but that board I've never seen work (and has its own PCB damage to where someone other than me did a bang-up "repair" of the CIAs and tore a bunch of pads off the board).

But seriously, if there's been any form of battery corrosion, start with removing both U177 and U178 - the computer doesn't need them to boot.  Replace both U975 and U976 and verify the integrity of all connections to these shift registers (primarily the clock and data lines) are all correct.  It's a bit of a blind stab in the dark, but this area is a very common cause of non-booting faults in the event of battery corrosion.  Even if everything visually "looks" OK.

Also check the analogue bias voltage is around +2.4V on U400/Paula pins 33 and 34.  Capacitor corrosion does bad things to the op-amp U402 which can ruin the bias in the entire analogue stage which can sometimes cause Paula to do some very unusual things.

Good to know. I'll give that a shot.

[Mr_Vanos]

Checked the Paula analog bias voltages as requested... they are +2.31V and +2.34V respectively.

I'm going to remove the RTC and U177 as suggested, and also some of the SIMM sockets for the fast ram (two for sure, maybe three), since there is some corrosion under there. Once I do that, I think I'm going to go back to basics and check the typical stuff.. power supplies good, resets, clocks, and also check the serial data from the io shift registers to see if they are any good.

I may also check that the keyboard data makes any sense too, just to see if the aftermarket keyboard is sending Amiga scancodes.

[rrete]

We wouldnt need to guess if the CPU is good or not if he does the CAPS LOCK trick I said earlier. This determines if the cpu is the problem or not.

Ok, I'had similar problems years ago with mine and original A3640 rev3.0 (actually upgraded to 3.2 & working in a A3000). I don't remember exactly but same problems fixed with, other accelerator first A3400 (now CS MK1 060) and resolder some cpu slot pins to mb.

It's only an option in base of my experience, I don't be sure that's the solution, of course.