Tandberg 3034 Cassette Deck - Recording & Erase not working

dave225

dave225

New Member
I have been reading old threads to try to diagnose this problem. Some of the symptoms have caused me to rule out a few common causes, but I could be wrong in my thinking .. and I'm at a dead-end on how to diagnose it.

Symptoms:
  • Pressing Record/Pause registers an input signal on the VU meters and passes the signal through to the monitor/out. (Level adjustment works - everything appears to work normally when paused...)
  • Pressing Record to start rolling the tape - meters & monitor still appear to be functioning - seems like it's recording.
  • on Playback - previously recorded audio still plays with no dropoff in levels. So - the erase head is doing nothing and the record head is doing nothing.
  • Play & record are the same head. They are making contact with the tape - I don't think I need to adjust the height - and playback indicates the head is in the right position.
  • These symptoms are in both channels.
  • I tried to measure voltage in the erase head - registered nothing, but no surprise - the problem is upstream from that.
This leads me to think the problem is in the oscillator? But I don't know crap about how an oscillator functions - just process of elimination leads me there .. or to a switch or a relay.

Can anyone help with zeroing in on the problem?





(If this helps... It's flipped so it matches the real board instead of solder-side.)
main board.png

svc manual: https://drive.google.com/file/d/1oVY6IACTMeN4YFGrINZYdcvAJ9vuuXG7/view?usp=sharing
 
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Oscillator not working is a good diagnosis, if you want to confirm it check for AC voltage at the erase head during record mode.

If no AC voltage is found there (should be several volts across that head), check Q651 to see if it's switching on when record is engaged; if so, there should be + DC voltage at the center tap of the T651 transformer primary that pops up when record is engaged. Then check Q652 and Q653 for flip-flop operation, they are providing alternating ground state to either side of T651 transformer primary. I think I'd also look at C654, the 100uF electrolytic cap that filters the + feed to the transformer primary.

John
 
jdurbin1 said:
Oscillator not working is a good diagnosis, if you want to confirm it check for AC voltage at the erase head during record mode.

If no AC voltage is found there (should be several volts across that head), check Q651 to see if it's switching on when record is engaged; if so, there should be + DC voltage at the center tap of the T651 transformer primary that pops up when record is engaged. Then check Q652 and Q653 for flip-flop operation, they are providing alternating ground state to either side of T651 transformer primary. I think I'd also look at C654, the 100uF electrolytic cap that filters the + feed to the transformer primary.

John
Click to expand...
Thanks @jdurbin1 . That gives me some places to test and/or rule out. Everything *seems* to be OK based on very rudimentary, non-mathematic readings -- uh, except still no voltage going to the erase head. I'm going to change C654 and see what that does. When I look at the board & try to trace continuity of where I could measure voltage, C654 looks like the weak link, although I do measure voltage across it.... about 1/2 of what the transformer outputs.
 
Excellent! Glad that helped out, I don't work on that deck very much so it was mostly a SWAG from looking at the schematic. What kind of cap came out of that location?

John
 
jdurbin1 said:
Excellent! Glad that helped out, I don't work on that deck very much so it was mostly a SWAG from looking at the schematic. What kind of cap came out of that location?

John
Click to expand...

100µF/25v - (standard electrolytic) I'm new to this ... (so not sure what kind of answer to give. :) )
 
Yeah, me either. They built these decks in Malaysia and I don't recognize that make at all, was sort of wondering if a Frako-branded part had been the cuplrit as is often the case with European-built machines.

But, a bad part is a bad part regardless of the brand!

John
 
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