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Old 16th Dec 2021, 12:37 pm   #74
Phantomrose1999's Avatar
Join Date: Mar 2008
Location: Melbourne, Victoria, Australia
Posts: 261
Default Re: Grundig TK27 - Low audio output

last post for the week, heading to sydney on the weekend.

Measured every voltage on the PCB according to the schematic, all are a little higher because i put 4 x diodes in. But close to what it should be

Took out the record / play switch to check, and found "at1.1" was not making contact when pushed in, so adjusted and was excited, maybe the record problem was fixed.

Tried record and the magic eye was not moving.. so no progress.

Tried play and the volume was still low so gone backwards

After pulsing the record switch very fast, basically like side stepping a clutch, and letting the switch come back fast under spring pressure, i now have full volume back. !!

I am still suspicious of "at1.4" as its shown very close in the service manual and maybe a timing issue with it. I opened it up to get more clearance in either position, as it was originally very close together.

Some questions please:

1) Should the magic eye move during play ? I think It used to do that and has stopped, forgot.

2) i tried it without the metal PCB shield and only got loud buzzing, so put it back.. I have put insulation tape on parts of the shield, as the original insulator came off. could it be oscillating that is causing the low volume..

3) My mobile phone when transmitting is causing the buzzing i kept hearing, put it in flight mode and the intermittent buzzing has gone. Never seen this before.

Anyway, i wont touch the record button for a week, and just see if play is
consistent as its working perfectly at the moment.

When i next get a chance, i will do it properly and connect a sig gen to the head input, and trace it through all stages with a cro..
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