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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 7th Aug 2018, 11:24 pm   #1
NorfolkDaveUK
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Default Tandberg 9000X only recording one side.

I have a Tandberg 9000X. I've never heard it play until now, as it had logic problems when I bought it and so, until today, I've never had it working.
It plays tape fine, both channels are playing back as they should and it sounds fantastic. It inputs fine as in both left and right channels have input audio. However, with the rec switches pressed in, both the VU`s light up, but only one needle is moving, and when playing back the recorded audio, only one channel has been recorded.

Can someone advise me on a course of action to take. I have re-capped the main board, and I have been over and over it and all caps are correct and orientated correctly.

Many thanks for all help.
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Old 7th Aug 2018, 11:42 pm   #2
julie_m
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Default Re: Tandberg 9000x only recording one side.

With the deck in "record", a good signal input to Line In of each channel and a stereo amplifier connected to the Line Outs, do you get a signal in both channels of the amplifier?

In the unlikely event of this being a three-head machine, you should have the monitoring switch set to "Source" for this test.
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Old 7th Aug 2018, 11:52 pm   #3
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Default Re: Tandberg 9000x only recording one side.

Hi Julie , it is a half track , 3 head machine . Yes I have good source signal with the machine in rec , with the monitoring set to source . However only one VU is showing signal there is stereo sound from the unit though .
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Old 8th Aug 2018, 12:09 am   #4
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Default Re: Tandberg 9000x only recording one side.

If you've got a few metres of sacrificial tape with programme on both channels, try recording a stereo source over it with the monitoring switch set to "Tape". What is coming out of the offending channel during recording? Silence means you have a good erase but the signal is getting lost -- we've already proved that it must be somewhere downstream of the monitor switch. The original sound means no erase -- so most probably, that channel is not even being armed for recording. That suggests a switch or relay fault.

Have you got a circuit diagram?
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Old 8th Aug 2018, 12:14 am   #5
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Default Re: Tandberg 9000x only recording one side.

im getting silence on the dead track so its the signal thats getting lost somewhere.

Yes I have the schematic .
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Old 8th Aug 2018, 12:28 am   #6
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Default Re: Tandberg 9000x only recording one side.

We know the signal is getting at least as far as the monitor switch, but not as far as the level meters. So that narrows it down to a few likely components. And we have a known-good copy of the same circuit. Start by comparing DC voltages on corresponding transistor / IC pins between the two channels. If necessary, you can probe for audio signals using your amplifier input, with a 0.1μF capacitor in series.
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Old 8th Aug 2018, 12:39 am   #7
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Default Re: Tandberg 9000x only recording one side.

OK thanks I will go have a poke around with the scope and see if I can narrow it down , thanks for your help . I`ll put a 10k sine into it in parallel and see if I can figure out where it disappears. I`m bound to get stuck but I`ll give it my best shot ..haha
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Old 8th Aug 2018, 12:56 am   #8
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Default Re: Tandberg 9000x only recording one side.

OK, I`ve just checked UA101 , pin 1 should have 13v , it has 25v , the corrresponding pin (13) for the right channel does have the correct voltage .
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Old 8th Aug 2018, 1:23 am   #9
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Default Re: Tandberg 9000x only recording one side.

OK so probing with the scope shows nothing coming out of pin 1 (L) of the op amp , there is a signal coming out of pin 13(R). So the signal either isn`t making is as far as the op amp or the op amp is the problem on the left side. I`ll carry this on tomorrow , I`m sweating like a pig in this heat time to call it a night I think .
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Old 8th Aug 2018, 1:27 am   #10
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Default Re: Tandberg 9000x only recording one side.

If there is a resistor from that pin to ground, it could have gone high-value. Otherwise, if the only thing pulling it low is the IC, that could well be faulty.
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Old 8th Aug 2018, 1:33 am   #11
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Default Re: Tandberg 9000x only recording one side.

There`s a resistor there but it seems ok .
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Old 8th Aug 2018, 1:35 am   #12
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Default Re: Tandberg 9000x only recording one side.

I have the 13v at pin 5 and the 23v at pin 3 , but i also have 23v at pin 1.
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Old 8th Aug 2018, 4:56 am   #13
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Default Re: Tandberg 9000x only recording one side.

What voltage do you measure on pin 6 of that IC?
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Old 8th Aug 2018, 9:04 am   #14
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Default Re: Tandberg 9000x only recording one side.

Could be a short or leaky capacitor in the feedback circuit. eg C112, C115, C116, C118

Do you get the same problem on all tape speeds? That would eliminate C116 and C118 if you get the same problem at all tape speeds.
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Old 8th Aug 2018, 9:15 am   #15
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Default Re: Tandberg 9000x only recording one side.

Hi ,
yes same problem at all tape speeds , but i believe the input and output voltage should be the same , so im pretty sure now the op amp is borked , i have recapped all the electrolytic caps with panasonics
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Old 8th Aug 2018, 11:20 am   #16
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Default Re: Tandberg 9000x only recording one side.

Quote:
Originally Posted by TonyDuell View Post
What voltage do you measure on pin 6 of that IC?
I have 5v at pin 6 of the IC
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Old 8th Aug 2018, 12:38 pm   #17
NorfolkDaveUK
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Default Re: Tandberg 9000x only recording one side.

Quote:
Originally Posted by JohnBHanson View Post
Could be a short or leaky capacitor in the feedback circuit. eg C112, C115, C116, C118

Do you get the same problem on all tape speeds? That would eliminate C116 and C118 if you get the same problem at all tape speeds.
I`m beginning to think you may be correct . I`ll report back once i`ve replace them all with film .
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Old 8th Aug 2018, 12:52 pm   #18
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Default Re: Tandberg 9000x only recording one side.

FIXED : it has those stupid stand up resistors and 2 were touching . Don`t you just hate those stupid things . They were hard to see too , poxy things .
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Old 8th Aug 2018, 4:06 pm   #19
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Default Re: Tandberg 9000x only recording one side.

Quote:
Originally Posted by NorfolkDaveUK View Post
Quote:
Originally Posted by TonyDuell View Post
What voltage do you measure on pin 6 of that IC?
I have 5v at pin 6 of the IC
I know you've now fixed it, but let me explain where I was going with that test.

If the IC really is an op-amp (and I have not check the data sheet to be sure) then unless the 2 inputs have essentially the same voltage the output will hit one of the supply rails.

Moreover, looking at the circuit you posted, there is a DC path, through resistors, from the output to pin 6. Everything else is connected to that via capacitors. So if you get a different DC voltage at pin 6 to that on the output then either

The IC is faulty and drawing a significant current through its input pin

One of those capacitors is leaky

There is another short somewhere (as you found)
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Old 8th Aug 2018, 5:14 pm   #20
NorfolkDaveUK
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Default Re: Tandberg 9000x only recording one side.

Thanks for that Tony. I like that you have explained that . Brain food is always good . Thank you .
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