On Sat, Oct 22, 2022 at 09:23 AM, Bill W1PA wrote:
If the finals are shorted, will the 817 not power up?
The finals are straight across the 13.8US (power unswitched), so they might well drag the supply down.
If the controller decides the voltage is too low, it will immediately power down.
The main power switching (for 5V,6V,9V) is done by Q1104 . I have had this fail. It failed high resistance, (i.e. there was some voltage, just not 12V)
From memory, the rig will power off immediately when this fails to switch on - probably because the main 5V will be low.
You can probe the switched 12V - TP1084 at the emitter of Q1082 - the big transistor by the 3x13VUS pins down to the PA, and the microphone socket. (block D2 on layout)
You can disconnect the the PA drivers with two jumper links on the transmit board next to the PA module.
There is a bare wire that connects the 13.8US to the PA module (finals) that you can lift to disconnect the finals.
It might be a good idea to do this while you play around getting the rest to run.
You should definitely not play around using batteries, best to use a variable supply set to 0.5A current limit.
On my version (-ND) there is a fuse for the 13V right before it goes down the 3 pins to the transmit board , (and another fuse for the battery). In the service manual diagrams, I don't see this fuse. (Perhaps that is part of the reason early ones destroy the transistors.)
