Tram D201 ALC not adjusting

[klj2497]

I checked d702 and d703 i replaced d703 because it made a steady peep when it was in the circuit, but when i removed it the old diode tested okay. the new diode did not get the r719 adjustment working again.

 

[nomadradio]

If C608 shorts, this shuts down limiting.

How much power does the radio show in SSB mode?

73

 

[klj2497]

it swings about 10watts on ssb there is no change up or down when i adjust r719 it does have power to r719 with 94vdc on the left pin the middle pin adjusts from 0 to over 70vdc and i think the right is ground.

 

[klj2497]

The c608 is a new capacitor, but i will check it

 

[nomadradio]

C608 has the positive side grounded. The board is marked with a "+" on the ground side of the cap. The cap is probably marked on the minus side.

73

 

[klj2497]

C608 is in the wrong way. the positive on the capacitor should be facing the front of the radio.

 

[klj2497]

its okay the positive side is grounded. the capacitor ground faces the front of the radio

 

[nomadradio]

Yeah, it sounds like a cop-out, but I'm accustomed using a 'scope to follow the negative ALC voltage from the trimpot at R718 while modulating the radio at full mike gain in SSB transmit.

If you get the modulated negative DC in step with the mike audio, turning R719 will show an erratic change if the trimpot is bad or just dirty. This can cause the ALC to cut out. If you get nothing here, the list of suspects is pretty short. The diodes D702 and D703 don't fail very often, but if the radio is connected to an antenna during a storm, a big surge can still come down the coax if a nearby tree is struck. Any time those diode check bad, the disc capacitor C714 that feeds RF to them could also be bad.

If everything checks okay there, you should have the same negative voltage at the white/blue wire at terminal B43 on the audio board.

Never tried to learn how to do this with just a meter.

73