Telefunken M15A - No Output At One Channel

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smilan

Well-known member
Joined
May 29, 2017
Messages
463
Hi, I'm in the process of calibrating this machine and one of the playback cards (25.5069.030.00) seems to be faulty.
There is no output signal on channel 1.
When I replaced between the output cards of the two channels there was output on channel 1 but no output at channel 2.
So it seems like the problem is in the channel 1 output card.
Since I don't have the extension card I'm testing this card with an external PSU.

I'm connecting +35V to pin 12 (+) and 0V to pins 16 and 17 and +26V to pin 9.
While injecting 1Khz at 2mV to pins 28 and 30, I can trace the signal at pin 13 of IS1 and IS2 as well as on pins 2 and 13 of IS3 and on the output terminals (pins 2 and 4 of the card).
There's no signal at pin 1 of IS1 and IS2.
So it looks like the 19cn/s amplifiers are not working.
If I'm not mistaken the signal coms from the secondary side of TR1, goes to TS1 and from there it goes to the inverting inputs of IS1 (pins 6 and 8). If I'm right I should see a signal on pins 1 and 13 at the same time, isn't it? If I'm wrong, there's anything I can do to navigate the signal into the 19cm/s amplifiers?
Schematic for this board at page 296
 
IS1 is a standard OP Amp.
If you have nothing on Pin1 the DC voltage must equal that of Pin 6 & Pin 5 because that is how they work.
If you have no signal at Pin 5 I would not expect a signal at Pin 1.
 
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