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nauseous 11-25-2021 04:28 AM

Apple IIgs RGB Color Monitor (A2M6014x)
1 Attachment(s)
Hi All,

I have an Apple IIgs RGB Monitor on the bench for repair that I am struggling to get working again. This is a 240v Australian Delivered model. I found the monitor at a local boot sale, seller was unable to provide any details if it worked or used to work etc.

Initial inspection revealed a blown 5 Watt wire wound resistor directly after the rectifier. I replaced the 5 watt resistor at the same time checked ESR on capacitors and replaced only those on primary side of power supply.
I happened to have a voltage regulator (STR54041) on hand so replaced this as well. Diodes / Resistors checking OK, I did find a Suspect 2SC1213 and used a BC337 as replacement whilst waiting on correct parts to arrive.

The monitor straight away blows the 5W resistor (R901), no smoke or failure - just goes open circuit.

At this point I have B+ isolated from the board and just using lightbulb for dummy load (Jumper B4 Disconnected from chassis).

The second time while running up on a variac - everything seemed OK till around the 200v mark when the Resistor failed open again. I could see the B+
was running a bit high around 128v but this was coming down as I increased the voltage on variac. (According to schema should be arround 115v)

Looking for any and all advice.
See R901 (5 Watt Resistor) highlighted in attachment.

Version 1 (Best):

Version 2:

Version 3 (Australia Amendments):

stj 11-25-2021 09:00 AM

Re: Apple IIgs RGB Color Monitor (A2M6014x)
i hope you have a dummy load on B+ like a 40w lamp.

pull J22 and see what happens - just to eliminate the possibility of an intermittent short in the primary capacitor.

eccerr0r 11-25-2021 01:28 PM

Re: Apple IIgs RGB Color Monitor (A2M6014x)
Was that C1213 really bad or just suspect? And make sure that you installed it right because the pinouts are different?

The "Version 1" circuit seems somewhat wrong IMHO, BTW.

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