Dead A4000 board

sjwaller

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Hi folks,

Just trying to revive a dead A4000 Rev B. board with soldered Buster 11.

Last time I used it there was an issue with the audio circuitry (leaky caps) and also some battery leakage. So I removed the battery and stored the board for later repair.

However, just went to test it out using a known working A3630 CPU card and it seems dead. I just get a black screen and noticed the clock crystal gets REALLY REALLY hot with / without the CPU card.

Does this sound like a dead crystal? I'm going to try replacing the crystal to see if that's the issue and also have a new set of caps on the way from Cosmos.

Failing that, any suggestions where I can send the board in the UK for repair or does anybody want to part-ex it with a working one?
 

davideo

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Hopefully Hikey will see your post (y)

If not try putting in a wanted/swap thread and see what happens.

Dave G :cool:
 

jvdbossc

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I would also use Hikey's service - he is ready, responsive and understands needsand personal wantings. He serviced my A4000 perfect

Keep in mind there are jumpers on Amiga's they are old hardware these day's. The clock source is important while fitting the slowest cpu board.

---------- Post added at 00:15 ---------- Previous post was at 00:14 ----------

Motherboard Jumpers

-----------------------------------------------------------------------------


A4000 Motherboard

------------------------------------------------
| ooo || oo | |
| Internal || DF1: | |
| Audio || Enable | |
| Connector || | Power |
| || | Supply |
| :: Mystery || | |
| :: Header || ooo | |
| :: (see below) || ooo | Fan |
| || ooo -------------|
| || Power Supply |
| || Connector |
| || |
| || -------------------|
| || | |
| || | |
| || | |
| || | Drive |
| || | Bays |
| || oo | |
| || SIMM | |
| || Size | |
| || | |
------------------------------------------------

Jumpers

J351: DF1 Enable
Closed: Enable low-density (880K) floppy as DF1.
Open: No DF1 *OR* for high-density (1.76M) DF1.

J852: Fast RAM SIMM Size (Chip RAM is always 2M.)
256K: 1M SIMMs.
1M : 4M SIMMs.

CN404: Internal Audio Connector
Audio signals attached here will be mixed with the A4000 audio
output. The A4000 audio is somewhat louder than the normal line
level output from most CD-ROM drives, presumably to make sound
effects audible over background music. Setting the software-
controlled A4000 audio level lower (to 32 instead of 64) will help
match the levels.

Pin 1: Audio In (Left)
Pin 2: Ground.
Pin 3: Audio In (Right)

"Mystery" Header (courtesy of Dave Haynie)

"There is a 12 pin header (DIL, J975) near the mouse ports. This feeds the
'extra' shift register in Lisa. Unlike OCS/ECS systems, which simply
multiplex the four quadrature signals from each mouse port with one
another, the AA systems serialize all eight bits of mouse data. While they
were at it, the AA designers added a second 8-bits to the mouse port
registers. These don't hook into mouse logic or anything, but they can be
read by the CPU.

So we used them for configuration. The first two bits (not on that header)
tell the OS about the AA system -- is it 16 or 32 bit, is it single or
double access per cycle. These are hard-wired on the motherboard. The
remaining six bits read high when unjumpered, low when jumpered. I had
recommended using one to say 'VGA only,' but there wasn't enough ROM
space."

Other Jumpers (Not Shown Above)

J100: CLK90 Clock Source
1-2 Closed: Internal (68020/68030)
2-3 Closed: External (68040)

J104: CPU Clock Source
1-2 Closed: Internal
2-3 Closed: External

J151: ROM Speed: 160 or 200 ns ROMs.
1-2 Closed: 200 ns ROMs (default).
2-3 Closed: 160 ns ROMs.

J213: Chip RAM: 2M or 8M
1-2 Closed: 2M Chip RAM (default).
2-3 Closed: 8M Chip RAM. This option was apparently for use
with the never-released AAA chip set, and won't
work in a normal A4000.

J500: Sync On Green
1-2 Closed: Sync on green disabled (default?).
2-3 Closed: Sync on green enabled

J501: Lisa Sync (Wide input on the Lisa chip.)
1-2 Closed: CSync from Agnus Pin 80.
2-3 Closed: +5V (default).

J502: Select DAC Sync
1-2 Closed: DAC syncs on green.
2-3 Closed: DAC uses standard signal (default).

J850: Enable DSACK (Used with 68020)
1-2 Closed: DSACK Enabled for 68020. U860 and U152 also required.
2-3 Closed: No DSACK.

"Haynie Kludge" Jumper (courtesy of Dave Haynie)

"That jumper enables the "early sizing" mode on the Zorro III bus. One
of the complaints about Zorro III is that the size of a transfer isn't
known until the data phase of the cycle. So in the Zorro III addendum I
added an optional mode that allows data size information to be latched in
the address phase. Just in case any existing boards have a problem with
this (if they go by the spec, they don't, but who really knows what
they're doing), it's shipped disabled. The idea was to test this out in
the A4000T, bless it as standard for future Zorro III controllers as long
as it did what designers wanted."
 
Last edited:

davideo

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That's a good point about the jumpers.

Have you got J100: and J104: set to INT

Dave G :cool:
 

sjwaller

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Thx for the info :) I had already set the jumpers correctly. Might try to get hold of Hikey ...
 
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