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Old 11-25-2021, 04:28 AM   #1
nauseous
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Join Date: Nov 2021
City & State: QLD
My Country: Australia
I'm a: Knowledge Seeker
Posts: 2
Default Apple IIgs RGB Color Monitor (A2M6014x)

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.
Thanks


See R901 (5 Watt Resistor) highlighted in attachment.

Schematics:
Version 1 (Best): https://console5.com/wiki/File:A2M60...-Schematic.png

Version 2: https://www.brutaldeluxe.fr/document...%20diagram.pdf

Version 3 (Australia Amendments): http://lukazi.blogspot.com/2013/02/i...placement.html
Attached Images
File Type: jpg Capture.JPG (154.1 KB, 8 views)

Last edited by nauseous; 11-25-2021 at 04:32 AM..
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