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I believe U33 runs the columns, I tested the rows chip (U47) while the unit was powered and it registers the rows in the chip, the columns don't do anything, the logic chips for it tests okay, but I

Transplanted the main CPU from the non-working board to the board that had the microprocessor error and it boots now, but I'm left with no keyboard functions so back to logic chips testing, probably

Haha thanks for the kind words, this thing has been an adventure. It's really testing my ability to troubleshoot components and also break stuff sometimes too. Had a bit of a setback, the used A7 card

Nathan, I don’t know if everyone feels the same way I do but I feel like with the progress and setbacks you’ve posted about I’m invested in hearing about the outcome! I’ve been following every

Thanks, seems to match, must be because the serial IO board is not hooked up so it can't change calibration or settings or something. the tests are just strange for voltages in MSDIAG. I did remove

Hi Nathan, Here are the wire colours and pinouts of the J8 &J9 connectors in the motherboard on my 8920A test set. To access the plugs (J8 & 9) I removed the modules A16, A17, and A 18 from the crate,

Hi Nathan, I'll run a meter over my 8921A mother board J 8 & 9, and see what I measure, reference GND. I have a drawing of the connections (connection diagram) somewhere, I will find that and attach

Main oscillator, that's good.. joking aside, I hope you have a speedy recovery. So, I have a question for anyone, on the J8 and J9 inputs on the mainboard, are they supposed to match the assembly

Hi Nathan, Great to see your progress mate. We seem to be similar in our tenacity to find the problem. I am also doing the "Change the Chips" routine on the I/O Board. I now have all the ICs, but fate

Well, I'm wrong, been wrong before, will be wrong again, definitely an issue with the serial IO board. Guess I wait for the chips to come in haha.

I had a whole thing typed on my phone, and accidentally hit back... wonderful. Anyways.. Some progress, a new Memory board fixed the Non-recoverable boot error as you know, basically it was acting

Yea I've been reflowing the chips to see if it's just a poor connection and probably gonna replace the chips that connect to the failing modules, not sure if the timer passes through it too. The

Hi Nathan, The I/O board is A5, in the card rack behind the control knob. It sits with the AF 1 & 2 boards and the Modulation Distribution board. The I/O is a fully digital board and is the one that

Replaced memory board and firmware error is gone, there is a host of other errors now, a timer failure and a lot of serial errors, the unit won't boot to the menu if the serial IO card is in so that

Update: found low sound, cracked diode on audio analyzer 1 board, rcvr synth and Gen synth still show out of lock, but still not sure if that occurs after boot up when cal field and other things are

Nevermind, found a blown CR1 switching diode, it's now 5v standby, still went to 12v when writing, still non-recoverable error. The fact sound is low or sometimes you can't hear it makes me think

Could someone please let me know what they get on tp4 vpp on the controller when not flashing? Just normal on.

Pulled and read the plcc20 palce 16v8h chip at U18 on the 08920-60395 board and the cmos portion comes up empty, unless it's programmed on the fly with the firmware the chip seems okay I guess. I did

Hi Nathan, My 8921A turns on the fan Immediately and there is white noise coming from the speaker if the volume is up and the squelch is CCW (Off). There are a few clicks, sounds like relays, as the

Just to update, I did some solder work, I swapped the flash and sram chips around to see if there was a flash or sram corruption that it would move the location of it when reflashed and give me a