transistor and relay problem

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Hi

I have an APT Pre amp with a relay which I am upgrading.

There are 3 transistors providing the drive and control to the relay(the circuit diagram does not match the actual circuit)- and the only way I can get the circuit to operate is by putting a DMM (either free standing battery version or rack mount version) across the base and collector, and hey presto it works- otherwise nothing no reassuring click.

The relays for unit this are unobtanium- I have replaced all the transistors in the drive circuit and all the diodes and resistors as well-

I feel I am missing something basic here, so any help appreciated
 
I have a badly hand drawn partial of that part of the circuit, which I have attached:

Q17 is a 2N3906
Q18 was a 2SC1345 now a KSC1845
Q19 is a 2N3904

thanks
 

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yes assiduously..:)

and the rectifiers (7918/7818) and a bunch of film caps and (as I have done on a previous unit that I use) all the IC's
I do like these APT's- but this relay thing has me flummoxed

If worst comes to worst, you can remove that circuit and install a different, new one.
There are several variations available, or you can design your own. Not hard
 
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Sounds to me like the base lead is open. Your drawing shows a 10k resistor from the base, but it is not clear what it connects to. if that path is open, the resistance of your mater to the voltage on the collector is apparently enough to turn on the circuit. Instead of a meter, try touching a 1 meg resistor from base to collector, does that also trigger the relay?
 
unfortunately all there are a number of versions of the pre amp- which a number of relay types, a narrow type (earlier I think), a wide type (the one I am working on- this is Revision 11) and a wide type on a daughter board (later than narrow, but before the one I am working on- I think)- and there is only one manual out there, which refers to the earlier versions. APT originally printed a circuit and attached this to the bottom of the units, however they are all the same and dont match the specific unit

thanks again for the help, I will figure out where to put the 10k (Q17 or Q19) and try and divine "why"
 
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