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.:roll:
@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.:huh:
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.
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.:roll:
@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.:huh:
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.
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