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-   -   Amiga 4000 - Black Screen (http://eab.abime.net/showthread.php?t=103382)

WStyle 02 August 2020 17:41

Amiga 4000 - Black Screen
 
Hello,

I'm working now sind some weeks on a Amiga 4000 Rev B Board.
I cleaned up the Varta damage and replaced the ICs in the area.

Checked all traces. Everything is fine. But I still get a black screen.
No Serial output with DiagROM. Tested another CPU Card. Same problem.
PSU and Voltages are okay. 15KHz at RGB out and 50Hz is okay.
Reset does not go from LOW to High.

The PowerLED does not "brighten" up. It still stays constant.

Any other clues what I can measure or test?

cpiac64 03 August 2020 13:34

test chip ricoh for verify if signal "power good " is ok (high)

Hedeon 03 August 2020 14:19

Correct jumper settings (INT/EXT) for the CPU board.

WStyle 03 August 2020 20:31

- INT/EXT already checked. Is on INT.
- Ricoh unsoldered cause I heard it should work without
- PowerGood only 1,28V instead of 5V

Hedeon 03 August 2020 20:41

3630?

Just asking as there is a lot of false info floating about. Even now on Amiga.org somebody linked the jumpers to cpu instead of cpu card (The A3000T thread)

Vypr 03 August 2020 21:51

By 'Power Good' are you referring to the _FAIL signal? it should be around 5V,if not something is pulling it down.
_FAIL signal feeds into Pin 2 on the Ricoh, Pin 15 on Ramsey and Pin 56 on Gary, if it's not 5V then the Amiga won't initilize. I had a similar issue on an A3000 where someone had replaced a cap with the wrong one (Had a 47uF instead of a 470uF)
There's no cap on this line that I can see so the only other component is R175 which should be a 470 ohm resistor.
First thing to do is chekc you are actually getting 5V from the PSU

WStyle 04 August 2020 20:21

Yes A3630.

So, checked everything again. On Ricoh Pin2 only 1.2V.
Checked R175. 470Ohm is correct.

5V is fine on PSU. Tested other PSU too.

Dont know what to do next... :-(

cpiac64 04 August 2020 21:39

force 5 volt on pin 18 of ricoh, use a diode 1n4007

WStyle 04 August 2020 22:40

Quote:

Originally Posted by cpiac64 (Post 1418403)
force 5 volt on pin 18 of ricoh, use a diode 1n4007

Forced.

There is a Diode between D178 and Pin 18.

Input on Diode between D178 hast 4,99V, Output 4.77V.
Input of my new Diode from Pin18 has 4.73V and on Pin2 I can measure 3.86V.

I can measure this 3.86V on the PowerGood at PSU Connector too.

Nothing changed. Still blackscreen.

quantum8 05 August 2020 02:40

How are the signals around U975 & U976?

These can commonly die and caused similar issues on my 4000. Booted right up after replacing them.

WStyle 05 August 2020 08:22

1 Attachment(s)
Hello,

I unsoldered and sanded the whole area and checked after this all traces and repaired some.

Most ICs are NEW.

Attachment 68388

DigitalKeeper 05 August 2020 13:24

Ramsey (U890) - Pin 15 (PWRUP) -> _FAIL MUST be at min. +4.8 Volt

AND

Gary (U150) - Pin 56 (Powerup) -> _FAIL MUST be at min.+4,8 Volt

if not -> the Board won't boot ;)

check the Power Connector's for Oxyd/Black Surfaces, and if there is no space between the plug and the connector; often there are shacky/waggly




Next "thing" - ya wrote "...Reset is Low..."

Check the Adress- and Data Lines for broken/corroded traces; in most cases -> at U975 & U976 the Area "looks" good, but it doesn't good :) -> that means - BOTH - Sides -> Top and Bottom ;)

Check, if the "MDAT" Line comes up -> look and check the Traces from U975 Pin 13 to Lisa Pin 20 - if this Line/Signal is not present - Lisa get "stuck" and System won't boot :cool

WStyle 05 August 2020 18:01

Hello DigitalKeeper,

I forced 5V and nothing changed.
Pin15 Ramsey and Pin56 Gary gets the 5V after forcing too.

PowerConnector is in good condition. Measured a lot of times.

Checked area U975 and U976 now a lot of times. Measured the traces to next target. Everything looks fine :-(

MDAT Signal is "weird". But maybe I'm too dumb to configure my osciloscope correctly :-(

U975 Pin13 (MDAT) to Lisa Pin20 measured. No problems.


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