Wednesday, 6 April 2016

PRC-320 Fault

My 'Test Bed' PRC-320, I may have mentioned, is faulty. How faulty I have yet to fully establish, but it seems some sort of power on stability issue.

Initially, I thought this would just be the expected leaky tantalums. So, I opted to replace these straight away. Module 9 has two of these

Physically removing the board in module 9 was fun! Getting it back onto the stack of PCBs and resoldering the wires was not! But, the two new 10uF 160v electrolytics were soon fitted 

Module 5, the power supply, was a bit more fiddly. For a start, the two PCBs that make this up are held together with these tiny circlips, which are incredibly springy! The first one off took me about 15min to find again!

And once open, the modules capacitors, C6 and C8, both axial types, were a little harder to replace with modern radial devices

But after a bit of fiddling, and some cursing that my new soldering iron tip hasnt yet tinned properly, the capacitors were replaced, the modules rebuilt and reinstalled.

Sadly, the fault remains just the same. So its clearly not these capacitors that are the problem.

The nature of the fault is hard to explain in words. So, Ive made a video of it! The radio had been off and disconnected from battery for 24h prior to this, and was only reconnected to the battery immediately before I started filming.

It will be a few days before im in a position to start module swapping, so in the meantime im hoping to pick the brains of some more experienced users on the forums. It may be someone has seen this issue before and can give me a hint where to start checking. If not, and since it has a 'supply fault' feel to it, i'll start with module 5 and module swap with my other set (I want to swap the front panel and main case from this one to my main one anyway) to see what changes move the fault.

Ive also today ordered some crimping tools. I had already ordered one for the 2.54mm crimp terminals (annoyingly today I found it a quid cheaper!) but decided id add to these ratchet type tools with one for Lucas automotive terminals (spade/bullet crimps etc), one for RJ type audio/data connectors, and one for RG58 cable RF connectors.

I have also ordered the remaining coax needed for the PRC-352. This is being made up for me by Mark. Once I have this, then the 20W amp will be usable in anger!

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