R2001C RF output has a DC voltage?

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crash
Posts: 26
Joined: Sun Oct 19, 2014 11:21 am
What radios do you own?: R2001C

R2001C RF output has a DC voltage?

Post by crash »

I have been working on an R2001C with minor problems, and I have noticed that the output RF rides on a positive DC voltage of about 3 volts, and I suspect it is NOT normal, IF, I read the schematic right.

On the A5A2 card, there is a circuit that has a bias network tied to the +5 volt bus. Sheet 3 of 3, there is a relay, K201-228-4-1a that connects the output to the inductor, L247, that is connected to the +5 volt bus. However, I do not know what the reason for that connection would be.

I have had a few failures where the unit goes into a reset mode and the screen has a warning of the failure of the non volatile ram and needing to be reset.
It has worked well after, except for the DC on the output. Do I need to see if the relay is stuck closed?
Jeff 'crash' Young N8CMQ
jry
Posts: 466
Joined: Fri Feb 06, 2004 3:14 pm

Re: R2001C RF output has a DC voltage?

Post by jry »

sounds like one of the components in the RF I/O has some leakage.

The R2001C had an odd RF I/O design.

Part of which was a diode switch path in parallel with the RF relay.

It's like they didn't believe the relay to engage the 50 ohm termination would be fast enough so they added an diode RF switch.

You should see if the unit is off around 28K to ground across the RF I/O which should get rid of most of the voltage normally

It may be that the CR110 switching diode has gotten leaky ....they are biased off at +30volts and then biased on with -12 when the wattmeter /high power load is on.

You could lift CR110 and see if that clears it and then swap CR110 and CR111 and see if that fixes it.

Looks like around 100 ua of leakage so not sure if that is normal or not for those diodes.
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