The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

I just received a President Jackson. It has RF power but seems week on modulation. Also it just has a buzz at receive no movement on the meter.Turn it on and it just buzzes.I got the radio for just about nothing so no big deal. Any Ideas on this one.? This is the radio with the heat sink in the rear.

I just discovered the buzz is only there when the antenna is pluged in. Oh the Board is PB-042AC

Check the voltage regulator and RX/TX switching transistors TR31, TR32, TR33 TR34 and TR501, the voltages are like so

TR31 (E = 7.50 RX) (E = 0.1 TX) (B = 8.15 RX) (B = 0.1 TX) (C = 8.50 RX/TX)

TR32 (E = 0.0 TX) (B = 0.85 TX) (C = 8.15 RX) (C = 0.10 TX)

TR33 (E = 8.50 RX/TX) (B = 0.5 TX) (C = 0 RX) (C = 8.35 TX)

TR34 (E = 1.05) (B = 1.65) (C = 12.80)

TR501 (E = 13.80) (B = 12.80) (C = 8.50)

All voltages are ? 5%

Also check that the Loop Osc and Carrier Osc are running and check IC2.

Is the fault the same in all modes?

Rick.

Thanks Rick
yes its the same except PA

So far I have checked the following.Results are.
TR -31 E-RX 7.47 TX .02
B-RX .01 TX .64
C-RX 8.24 TX -minus .13
TR-32 E-RX .63
B-TX .14
C-RX8.27 TX .10
TR-33 E-RX 8.00 TX 7.6
B-TX 8.32
C-RX 8.6 TX 8.48
TR-34 E-1.54
B-.99
C-13.10
TR-501-E 13.76
C 8.64
B 13.10

From the voltages, you have told us there is a fault around TR31, TR32, and TR33, it looks like TR31, and TR33 have gone short, you need to replace them with the right ones as subs offend fail TR31 should be 2SD355 TR33 2SB525 and TR32 2SC945. Also check R202 (1K) R203 (2K2) D66 (IS2075 you can use a 1N4148) D49 (5.1 volt Zener). Try removing TR33 and the RX may come back, I say this as the collector has volts in RX and TX (according to your voltages) it should only have volts in TX.

Rick.

I haven't had time to do much to this but today im off work and plan to get to it. A strange thing I noticed this morning the radio is missing TR-41.I The schematic has it shown so I plan to also replace it.I realy do appericate all your help Rick.

Thanks a bunch!

looks like this project is on hold untill i can find a parts supplier.

well i have receive now but no audio in receive i think i have audio on transmitt as the needle swings as it should