Monday, 13 June 2016

S-Meter mod...and faults!

Almost all the mods are done now on the Testbed RT-320. The final 'official' mod to do was the S-meter. To do this one, Assy 6 had to come up again, to access the meter switch

The pink wire going off the side of the radio in the lower right of the above picture is this connection. Next up was to make up the diode chain that would take the AGC voltage and create a drive for the meter

Ive hot melt glued this down to the PCB, with the ends exposed, that way I can easily unsolder the wire to the switch in order to remove the PCB. In the picture below I think I have it connected to the wrong place on the PCB! Im waiting for clarification on that. At present, this mod isnt working, see below!

With all these mods completed, I put the set to the test - not good! Now, I had a suspicion that this set wasnt performing very well, so I suspect this is all part of, but it seems that the set cant receive my test set signal, and on Tx its also off frequency. A very very strong input signal from the test set it can just receive, but again off frequency, yet the synthesizer is locked and functioning! Also odd, there is no AGC voltage (so the above S-meter mod doesnt work!). But perhaps the strangest issue - If I put it to antenna, I can receive RAF Volmet on 5.450MHz ok but distorted, yet if I tune to Shannon Volmet at 5.505MHz, it doesnt hear anything! This despite Shannon being much stronger than the RAF! Also, I can tune in an AM broadcast using the SSB mode, again ok but distorted, yet hardly hear anything of it in AM mode!?

So, something is definately amiss in this radio. And I suspect its going to be a pig to solve. I will complete the mods necessary for the Remote Control Project before trying to fix the fault(s), as the one remaining mod is to add the ribbon cable to the synthesizer inputs, and that will be useful for fault finding!

On another note, I have a PRC-350 on order from LRseries near York, likely to be a project job in itself, plus an EKGSA kit to allow me to use the GSA antenna on one of my 5.4m masts. Ive also taken a punt on a pair of PRC-349s - no use for amateur bands but they are full CES kits so might prove fun, but at any rate will complete the collection.

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