A4000 Tips for repair.

[psodas]

16/05/10
In Amiga 4000 who no boot, (dark grey condition) CIA in place U350 was defective. After replace, machine boot again normally.

In the same A4000 with a good or a bad or without CIA in place U300, this had no effect at booting sequence!!

Also A4000 with Green screen symptom, with or without chip ram simm in place, has cut the line between R79 and his hole. After repair machine boot again.

This resistor was in the front end of LocalBus Coprocessor Connector mark PIN1, at the bottom side of the pcb.

@26/05/10

Also, A4000 with "Guru Meditation" at boot sequence before "insert disk" screen, has U177 (74HCT174 type) defective. Its place is near the backup battery.



@28/05/10
Very strange problems may create a defective Ricoh 5C01 real time clock IC, as red screen, yellow screen, or not boot at all.
Also recently encountered a very strange problem was as follows.
In an A4000 who boot normaly from cold start and work perfect, if someone push off and on again the mains switch, has as result a dark grey screen. After two minutes with the machine OFF, when the restart all work perfect again!!! This was repeated.

The problem was the Ricoh ic. For some reason degrade its suply voltage from +5v, to 1.77v!!!! This was happened only if someone shut and then restart the machine from a previews working condition.

At first I think cause the ic was defective, but later discover cause in some pcbs, must add a 1N4001 diode from D178, to Ricoh ic at pin 20. The cathode of diode must connect at pin 20 of ic.


@7/06/10
Amiga 4000 with boot screen sequence <<dark grey - yellow>>, has Alice U211 ic defective.

Also if Amiga 4000 does not recognize any fast ram, usually one of four buffer ic 74F245 (U891-892-893-894) may defective. Most likely is U891 who is near in backup clock battery, and has corroded from battery leak.

@8/06/10
Also with defective, or without being in his place CIA U300 (responsible for serial port), floppy drive doesnt work.

@13/06/10
If some of joy ports operate intermmitently or not at all, ussually one of two 74HCT166 ic is defective. These are located near in battery of RTC.

[Cosmos]

I have an A4000D rev B with red screen !

Roms checked : ok
RTC checked : ok

Without the 2Mo chipram, no green screen...


Any ideas ?

[psodas]

Hi Cosmos.
I any case I am not an Amiga Guru. Experiences that I have is from personal attemts at repair.

I believe cause you have check the proccessor board and its Ok!?

Is possible to check Cia? U350 one.

[Cosmos]

Yes, the cpu card is good too !

For U350, I need to desolder...


And I'm looking for an hack to get 2 Mo of chipmem with a simm 4 Mo ! Any ideas ?

Or where to find a 2 Mo simm ?

[rkauer]

Cosmos, you can use a dual-sided 8Mb stick on the chip mem slot without hassle, mate.

BTW: how's Dieter's CPU going?

[Cosmos]

>8Mb stick on the chip mem slot without hassle

Ok

I found that : http://www.leboncoin.fr/informatique...33.htm?ca=10_s

Will works ??


>how's Dieter's CPU going

I'm very busy with my next patch... Which library this time ???

I'm training on my 604e, I'll try on the G4 tomorrow !

[rkauer]

Sounds OK to me.

[Zetr0]

@Cosmos

any 2MB, 4MB or 8MB [double sided] SIMM will work as 2MB CHIP in the A4000

Latency is an issue so make sure you can get 60ns or 70ns at the slowest, I had some trouble with 80ns double sided SIMMS


this is all so weird, I recieved my order from Farnell today - enough to re-cap 2x A1200's and 2x A4000

also all the SMD components for replacing the following from 2 A4000 motherboards - 74HCT166 - both serial shift registers (mouse/joystick ports)
74LS174 - dual flip flop - positive edge trigger (memory mux)
74F245 - Bi-Directional Octal Transceiver (memory)

looks likes some work ahead of me... - may even make a you tubie =)

[Cosmos]

Ok, U350 on socket and changed : no more red screen ! Thanks Psodas !


But :

with chipmem : green screen, white screen, green screen...

without chipmem : NO green screen...


I changed all capacitors, same prob...


So what now ??

[psodas]

Hi again Cosmos.

The new CIA is tested that is in good condition?

Is the extra 1N4001 diode from D178 to Ricoh ic at pin 20, in her place?

Also check for continuity the line between R79 and his hole.
This resistor was in the front end of LocalBus Coprocessor Connector mark PIN1, at the bottom side of the pcb.

Fat Buster if defective usually have a yellow screen, but check yours if it is in a socket.

Check also in all custom ics if you have the reset lines. Must be 4.6 - 5 volt.

Check the 24 x 68(maybe varies) Ohm resistors near Lisa U450, if its Ok.

---------- Post added at 03:11 ---------- Previous post was at 02:02 ----------

Can anyone know were can I find spare parts for AmigaOne-XE/G4 from Eyetech? I need the CPU power supply 5 bit controller CS5155, who is not specific for Amiga, but I can not find anywhere.

For your information, never try to use this computer without heatsink and fan in cpu. If so, after some minutes you destroy the controller, Hexfets, and propably the main CPU.