PRC320 slow tx/rx recovery - fixed?

Having spent a long time investigating the slave relay 6RLA (the relay on the unit 6 motherboard that switches the tx/rx 6v line and the IF signal), using tacked on LEDs to observe the DC rails, and 'dry' testing of the IF contacts using continuity testing and an external supply to activate the relay, I started to come to the conclusion that whatever was causing the fault was not associated with the physical switching. I couldnt positively rule it out, but my suspicion began to fall elsewhere.

In particular, it fell on module 6b - the Receive Audio module. This contains the demodulator/detector, audio stages, and AGC circuitry. I noted in particular the presence of one of the suspect tantalum capacitors in its supply rail, isolated from the rest of the radio by a 100 ohm resistance.

So, today I embarked on the task of swapping this module for the one from the test-bed radio. Not a simple task!

18 soldered connections and 3 bolts!

 There are 18 connections, plus 3 bolts, to module 6b. Each is made via a link wire, looped around the module pin. Each had to be desoldered and lifted, the pin cleaned, the bolts unfastened, and the module withdrawn, first on the spare module from the test-bed radio, then the one from the faulty radio.

Since I had the test-bed open and was removing 6b, I decided to also remove module 6a - the Receive IF stage. This is located beside module 6b, and would be the next suspect in the investigation!

module 6b (left) and 6a (right)

After removing these from the test-bed, they were carefully put aside. The same was then done to the faulty radio, only this time removing just module 6b. With that put safely away from either the radios or the previously removed modules, to ensure they didnt get mixed up I immediately installed the spare 6b module into the faulty radio.

With the module replaced and reconnected, and a couple of the chassis screws replaced to ensure ground continuity - I made a brew and a sandwich!

Refreshed, I reconnected unit 2 (the rear section), the handset and the battery, and began testing...

At present, I am testing with a dummy load connected of course. Carrying out several key up/down tests, with various times in Tx mode, on various modes, and with some modulation, it does seem that there is no longer a delay in returning to receive, at least no longer than the momentary pause as the relays drop out.

Next, I need to completely reassemble the radio, and ensure it continues to operate like this. Then, I will need to replace the dummy load with an antenna connection and test the receiver with live signal. Only then will I really know if the set is fixed. But im moderately hopeful!

If it does indeed turn out to be working now, then the fault is with the 6b module, which I will need to repair before putting it back into service in the test-bed. The photo below shows the inside of module 6b... im not looking forward to fault finding this thing!

Inside No. 9, sorry, 6b...