PRC344 is alive

After repairing the 6v and 12v regulator modules, and proactively replacing the same capacitor in the 3v module, I now have a working PRC344 UHF AM transceiver.

Thanks to Alan G8LIT, I now have the EMERs for this radio, so further repair and alignment should be much easier. Ive already set up the various voltage rails correctly (most were a little low), but the receiver is still somewhat down. Further alignment will wait until I have printed out the instructions. There is also still an issue with the fit of the battle antenna, which refuses to rotate into the locked position.

One thing I have been able to do, now I have the information to work it out, is disable the transmitter! I had thought I would have to unsolder the supply rails etc to the transmit section modules in order to ensure none of the various ways that the radio can be put into transmit would operate, but it turns out that all the transmit controls are dealt with by module3, simply pulling this out totally disables the transmitter with no other detriment.

A few design flaws show themselves with this radio. The first is with its carrying method. It was intended to be fastened to a carrying harness using an adapter plate that used straps to hold the radio, and as such there are no bolt holes for the normal GS adapter plate as used with the PRC351. But, the radio is also very heavy and very square - which means just picking it up is awkward as theres nothing to easily get hold of! Second, internally there are several adjustable parts which have the same designation as each other! For instance, all the regulator modules are adjusted by an R7. This means that if you accidentally pick the wrong module you could cause quite some damage by adjusting the wrong supply rail!

Ive spent some time today clearing and tidying the RF bench, which really was cluttered up. This was mostly in order to find a place for my new variable bench power supply. In doing so, I decided to also rationalise and maximise the space used by the test equipment, so the test bench is much tidier now and more compact, less wasted space ('scope now on top of the Marconi, PSU on top of high power test load, frequency counter on top of the spectrum analyser). This created enough space that ive been able to put a couple of stackable bins next to the test kit to hold short coax leads and test leads/scope probes etc.

Ive already laid out the next job on the bench, which is the band change modifications to my Pye PF8. This task involves swapping five very small ceramic capacitors, to swap the radio from the U0 band to the T1 band, which covers 70cm. With these capacitors changed, I should hopefully be able to peak the radio up on 70cm without having to hit the bottom of the coils!