Ok so I bought this mark 1 Jumbo in nice condition all seemed fine until the other day i had it switched on receiving and all of a sudden a huge buzz and crackle coming out of the speaker. Also the same happening on TX audio too.
I first checked the power supply at 13.8v and it's fine, I even tried it on a seperate power supply but the problem still exists. I then noticed the squelch mod had been done which i thought it must have as the squelch didn't pop but on SSB if there were no signals the squelch would close even though it was set minimum which i thought was a bit odd. Anyway i have now put the squelch back to standard and even though this buzz/crackle is still there I can just about hear the squelch thumping in so that would seem ok.
I then checked the voltages on the audio amp (TA7205P) according to the schematic i have. Some of the voltages are incorrect but not all. So i replaced the chip with a new one but still no cigar ! So i then looked at pin 6 amp input it shud be 3.4v but is reading low. So i followed it back to Q34 and there should be 3.4v there but it is low there too. I checked the 2 other transistors further back in the chain and they were reading correct voltages. So i pulled Q34 and checked it on a multimeter and it seemed roughly ok as in readings in the correct leg order etc. So i've put that back in circuit and have tested some of the diodes, resistors and capacitors that are around that area and they all check out fine.
I suppose I should try replacing Q34 but it did seem ok on the multimeter unless that is an unreliable way of checking. Im at a bit of a loss now ?
So just wondering if any of you guys have any experience as to what could be the issue here? I appreciate any help.Regards,
Dom.
