Try unplugging the "OUT PUT" plug.

That'll disconnect it for sure, plus a heap of other wires. Doesn't matter? Okay I'll do that. I'm looking for DC voltages here, right?

 

Yes, DC. It looks like normal is +32V for B+ and -32V for B-. But I expect it to be a lot lower. I'm interested to see if they are both about the same.

 

Measuring the transistors TR6 and TR7 in circuit may not work as the B-E resistor is so low.
Undoing the screw that has the Collector connection will let you test from the Collector (case) to Emitter for shorts without the rest of the circuit causing problems. Try that asd see what the reading is.

 

I got -28 on B- and 28 on B+

I will unscrew the collector on the transistors and measure them again. We're talking disconnected again, there no power?

 

Yes, no power.
There should not be a short C-E of the transistors.
If that measures ok, put the screws back then power it up and measure the volts on the output. That is pin 4 of the OUT PUT socket. That should be close to 0V.

 

C-E I have TR7 Black on C, Red on E : 577
Red on C, Black on E: 1

TR6 Black on C, Red on E: 523
Red on C, Black on E: 1

The other measurements are:

TR7: Red on Base: to E, 309, to C 344 Black on Base: to E: 336, to C: 1


TR6 Red on Base: to E: 310, to C: 346. Black on Base: to E: 333, to C: 1


So I think that measures okay, does it? 309, etc. is not a short, I think? I'm not sure what it is to tell the truth. I think it is supposed to be the voltage drop across the junction (I'm using that diode measuring feature) and so I suppose it is 0.309 V unless it's a percentage of whatever volts....

So I'll make a coffee and if you haven't got back by then to tell me don't do it I'll go ahead and reassemble and measure the output voltage.

learning heaps here...

 

Go ahead. As far as I can see, those look ok.
If you like coffee, this is what I made for a mate of mine for his birthday...
https://www.thingiverse.com/thing:3260433

 

Less than 1 volt indicates the forward voltage drop on the junction, according to your DMM manual.

Si (silicon) can be 0.45 -0.8 volts
Ge(germanium) is typically 0.3 volts

 

Right. So the 309 etc. mean 0.309 volts, as I thought it might. All good. So they're germanium transistors I guess?

I got 0.123V on pin four of the (removed) outlet plug.

That's a great cake. And it's for a machine to make, I think? One of these new fangled printers? And that was the code for it? Very interesting. I'd like to get into that but don't know when/how.

so where am I now? Haven't found the problem but have eradicated some possibilities?

 

It looks like the measurements are ok. I'm a bit stumped.
Is the lamp still lit with no speaker connected?
And that thing I 3D printed is not a cake, but a clock face. So it is "coffee o'clock" all the time

 

Oh... I thought it was a coffee clock cake...

Yep, the light is on with the output plug out. As long as the organ is switched on the light is switched on.

Light goes off if I switch the organ off.

And the light is fairly dim. What does that tell us?

Because when I build the thing and tested in the shed I used another light to plug into it in lieu of the organ and when I did that the other light was dim and the test light was bright.

That means anything at all?

Any ideas where I should look next, what I should do?

 

You said the B+ and - was 24 Volts.

Can you tell me how the primary is connected as that can be variable.

This is a cut from the technical manual

 

Don't exactly know what you mean, Joe.

I take it you're talking about those different circuits up there involving the transformer.

Mine should be the Australian spec, if so, I'm in Australia.

I don't know where to look to check that though. If you can help me with that I'll look.

I was also wondering about how sure are we the problem is in the amp circuit? Are all those other circuit boards in the manual (the amp circuit is the only one that doesn't have a pic of the underneath ) eliminated already, we know that? Or should I be looking at finding methods to do that?

 

So the 309 etc. mean 0.309 volts, as I thought it might. All good. So they're germanium transistors I guess?

So did I at first. However the datasheet says they are Si. Like dendad said, in circuit can produce unusual results. You were looking for something other then a very low reading.


Given the information you provided about the transistors and diodes, the voltages being the same, and you not finding any other problems.
The only thing that makes sense to me is you have the improper fuse in F3. I would recommend you use at the minimum a 2.5A slow blow.

You would need more test equipment than a DMM to solve more complex problems.

 

Two things about that though, Joe: it worked fine here for a nearly a couple of years with the 1.5A in it and that fuse was the original, authentic, factory supplied I'd say - because it has that little red dot on it that the spares in their packet have.

They've actually got red dots on lots of their components on the board. Must be a thing they do.

If I did try a heavier fuse what potential damage could I do?

p.s. and would you be confident the problem is in that amp circuit?

and seeing as it comes out so easy I'm now in a position to be able to take it down to Adelaide maybe - could it be perhaps fixed that way - i.e. removed from the rest of the organ?

p.p.s. i took a look at your .pdf files and I like them, much. planning to perhaps work my way through them if I can..

 

F3 only serves that amplifier on that main board. It is the reference point for both the B+ and B-. Those two signals go no where else, so the schematic we see on that page is all that is involved.

Now, you had not mentioned it had worked fine for a couple of years prior.

Ok, further testing should be done.

If you accidentally touched both the base and collector when testing the transistor with the + lead on the base and - lead on the emitter, you can get the 0.3V you have observed. That may not have been the case, especially with all the tests you have done.

Tr4, Tr5, Tr6, and Tr7 should be desoldered and checked out of the circuit.

 

well I did say '..and it just broke..', Joe.

Good to know it's confined to this board. Excellent.

I'll recheck the 0.3 observations.

Then I'll desolder and check. That's going to be a first for me. I can see it'll be a bit of a job because they've done such an excellent job on this board that the ends of the legs are bent over before soldering. So I can't just desolder to melting and pull.

I might be wise to invest in a good solder sucker or something.

Thanks for hanging in and helping.

 

I would use a solder wick, and not a puller.

 

thanks for the tip. I'll go that way. It's all unexplored ground for me. And I was thinking considering I'll have to cut off those turned over ends and the transistors are so old maybe I should just invest in new ones - check the old for information but put new ones in anyway?

 

you shouldn't have to cut the transistors out as once you wick the solder ... you can move them easily.