Thanks Rick,
I suppose that's $US + Wads more for USPS.? Always a problem for OZ. We are more part of Asia, but most of their stuff is Consumer quality.
I have been reading the manuals from IO Groups, in fact I have printed and bound them in two Volumes plus the Circuit diagrams separately.
I have done the Power supplies RE-Cap and they are all trimmed and working fine. I have replaced the Back-Up Battery on the Memory boards
I actually have two 8920 Test sets, one is 8921A, and the other is 8920A. The 8921A looks in the best condition, so I am concentrating on that. I did a bit of swapping and using RF-DIAGS and AF Diags. (Great Fun). I checked the +5 & -5V reference, that's OK. A9 Voltage is 5.072 on my 8022 Fluke Meter. (The best I have).
RF-DIAG? went well up to the receiver test where is showed failures in AM & SSB Demod. I swapped the RX Module from the 8920a ,and ran the tests again, same result. so I suspect RX module is NOT really the fault. The Spec An, CRO, and RF Gen seems all Ok. The OXCO is spot on. So that is one item I will deal with .. Works In Progress (WIP).
?On the AF-DIAGS I was able to determine which boards are suspect. The Preliminary Paths tests in AF-DIAGS is where the errors start. The first test, of AF Generators 1&2 run "No Failures".
The Prelim AF Paths Test produce 9 Failures!? and a code 511 (unable to determine failure). And on another run through, I had a Code 373. this pointed to the A4 Board being a high chance of being faulty
Reading the specific Diagnostic? descriptions Chapter 11 of the AF tests, Page 600 of the Manual describes the Modulation Distribution Board functions during the tests. It seems to me that there is a switch that is stuck in the Source or the Monitor select Multiplexer, or both.? Mod Distribution Internal Test produced a Code 119.
So this is where I'm at.
My background is in Medical Electronics, CT, MRI, Ultrasound , Gamma Cameras .. etc.( ~30 years) I have a pretty complete workshop for Electronic service, including SMC soldering. I am going to have a go at component level repair, if you could steer me to which chip to measure and prove as the culprit.
I have a Tektronics 2230 CRO and a Siemens, Ancient but very stable, AF generator (Level Generator). One of my careers was as a Scientific Instrument maker, so I am Old but no slouch (78yo). So this project is for keeping the "Grey Cells" Stirred.
Please help if you can.
Regards
Bill Macham ??? VK6IC
Millendon W.Aust.
618 9296 0137
Westwill1@...
