Amiga 2000 - only black screen on boot

[petr22]

Hi, I recently bought A2000 in non-functional state (without floppy) and since then I am trying to repair it, as it is amazing computer. Computer look complete (only floppy is missing) with board revision 4.3 with ROM 1.2. Of course original battery leaked long time ago. What I done until now:

- repaired leaked battery damage - replaced R914 resistor and damaged CPU socket, damaged CPU board socket is still in place (there is no short between pins) as replacement part is expensive and not mandatory to have yet
- original battery is removed
- triple checked all connections leading from CPU socket, no damage
- repaired A2000 PSU which came with the computer (broken diode)
- reseated every IC which can be removed without soldering
- cleaned the board

As it does not fix the problem, I suspected one of the ICs can be bad, therefore I replaced them with ICs from two non-working A500 boards I bought for parts. No change with A2000, but when original ICs were returned to A500 boards, both A500 boards suddenly works (something was telling me to try to test them after all ICs vere reseated..) - therefore I swapped again all ICs from A2000 one by one to test them in A500 - everything is OK, only with Agnus (8370) from A2000 Amiga 500 display Kickstart hand for few seconds and then picture is distorted -therefore I thing this Agnus is bad and I replaced it in A2000 by 8372A from one of the A500s, but it does not fix black screen.

- when PSU is turned on, screen blinks as signal is recognized, but stay black
- caps lock can be turned on or off, but does not blink on startup (error code)
- tried floppy from A500, no signs of usage
- tried floppy from A1200, no signs of usage
- computer can be "rebooted" by Ctrl+Amiga+Amiga

Regarding to documenantion, it should not be possible to start A2000 without DF0 floppy and keyboard connected, as CPU is hold in HALT state without the correct signal.

Can you please recommend me what can be checked next?

[Franchute13]

Hi petr22.

Check power led... is blinking?

[petr22]

Hi, I forgot to mention it - power LED is always off, but I am not sure where it should be connected - now it is connected to CN306 on the corner of the motherboard, right below the LED plastic mount. As there is no HDD, HDD LED is not connected.

I found some pictures of LED connenction, but they are different - some of them show wires connected to pin 1 and 3 and some to pin 1 and 2.

Found the correct pinout - black wire pin1, red wire pin2. Power LED is on when switch on the PSU is pressed and stay on whole time, no blinking, solid green light.

My teory is that there is error which is not detected as error by board logic or it wait for something.

[Franchute13]

You can upload a high quality picture of motherboard? One o more picture. Two side.
Sorry for my english

[petr22]

Upper side of the motherboard.

[Franchute13]

Check jumper position
http://www.bigbookofamigahardware.co...000rev43mb.jpg

Check PSU, pin 14 (TICK)

[petr22]

It is same with J300 jumper in both position. I swaped Denise with a IC from A500, original Denise from A2000 works in A500.

[cpiac64]

you need verify if pin of kickstart is connected to cpu, only one is not connected with cpu

[Franchute13]

What happens if you remove ROM? power led blinking? color screen?

[petr22]

Without the ROM it is still the same - solid green light and black screen (tried with 100% working 1.2 and 1.3 ROMs).

[Franchute13]

Originally Posted by petr22

Without the ROM it is still the same - solid green light and black screen (tried with 100% working 1.2 and 1.3 ROMs).

Green = problem with RAM, AGNUS or trace between this chip.
Check 74F244 (u540, u541)

Some of the ram chip is hot?

[hooverphonique]

Originally Posted by Franchute13

Green = problem with RAM, AGNUS or trace between this chip.
Check 74F244 (u540, u541)

Some of the ram chip is hot?

the green light is referring to the power led, not the screen..

and talking about blinking power led or screen colour without rom is nonsense - without the rom, there is no code to execute, so the system will do "nothing".

[petr22]

All RAM chips are cool, only Agnus, Denise and CPU are warm (just a little).

Currently used Agnus works in A500, therefore it should be OK (original Agnus from A2000 does not work correctly in A500).

Pin 14 from PSU (tick) is OK.

[Franchute13]

Originally Posted by hooverphonique

the green light is referring to the power led, not the screen..

.

OPPSS, my mistake, sorry.

[Franchute13]

Petr22, What video output are using? The RCA or DB23?

[petr22]

Mono RCA output, but there is no output on DB23 either (checked with oscilloscope in the lab). RGB cable for my Amiga is already ordered (I know, I should ordered it 23 years ago).

Is it possible to check 74F244 with simple multimeter (which I have here)?

[Franchute13]

Originally Posted by petr22

Is it possible to check 74F244 with simple multimeter (which I have here)?

You need check 74f244 if you get green screen. In this case don´t check 74f244. sorry, my mistake.

This PDF maybe help to check traces.
http://www.amigawiki.org/dnl/schematics/A2000_R6.pdf

[cpiac64]

have checked if have continuity from pin of kick and pin of cpu?

Page 6 of schematics U500

i have repaired ten a2000 with broken connection

[petr22]

It is strange - multimeter shows that all ROM pins are connected to CPU (one side to upper right half of pins, other side to lower right pins).

[cpiac64]

ok
change socket of fat agnus