Discussion in 'Amateur Radio Amplifiers' started by W2PPJ, Nov 3, 2017.
i was checking out your website impressive!!
i checked 208 & 209 infininty [OL] on both.
So if you measure from the top end of C208 (or C209), does it still show a short circuit (ie zero resistance)?
If so, and it's NOT C208 or C209 that has failed, then you must simply have a trapped wire shorting to the chassis somewhere - ie the wire that goes from C208 to the big green Bias resistor under the chassis . . . or the wire from that resistor to the RY terminal on the back.
Did you check to see if S4 was internally shorted?
That wouldn't cause a problem . . .
The relay should only go over when the RY terminal (on the back) is shorted to ground AND S4 is in the OPERATE (up) position.
The fact that his relay is on all the time, even with that switch down, proves he must have a short on the line that goes from the bias resistor (R4) to C208 and C209.
no resistance on 208 and 209 slowly climbs .
Roger, doesn't the standby switch S4 break the line out to the relay that eventually gets grounded? Doesn't S4 have one of its legs grounded? What if S4 is internally shorted and that the relay line is grounded through S4 internally? Impossible?
I would have thought that very unlikely (I've never known these switches fail at all!) . . . but yes, if it had an internal short to chassis, it WOULD cause this fault.
To W2PPJ - you know the the big green bias resistor (under the chassis) - what is the resistance on each side of it to chassis?
S4 is a DPST switch. One pole simply drives PL2 "OPER" ON/OFF. The other pole interrupts the line from the RY terminal on J5:
(click for yuuge image)
IMO, it would be highly unlikely for toggle switch S4 to be shorted between poles. However, it could be connected wrong.