XOX(BOX) Trouble shooting

[guest]

clean the flux off if you havent already. if that doesnt do it, one of those transistors is bad.

[spotta]

I'll have a good clean around the VCO tonight, I think I also have spares of two of those Transistors, I'll let you know how I get on.
Thanks for all your help so far.

[guest]

if you want to be sure of which parts are bad before having to buy new ones/replace them, you can do the following test:

1. remove q25
2. put your multimeter in current mode, and measure the current between the collector and emitter pcb holes where q25 was. this will be the holes that go to q27 and q26.
3. play the lowest C, and then one octave up, and then another octave up, and so on until youve gone through the full range. the current should read around 3uA, 6uA, 12uA, 24uA, 48uA. the actual values might be different, but the thing to look for is a doubling of current with every octave.
4. if your meter doesnt measure current down to the uA range, then you can put a 100k resistor in these holes and measure the voltage across it (put one lead on each side of the resistor), and the voltage across it should double. but, a low quality meter might have trouble with this as well.

if the current doubles as described, then the problem is with q24,25, or 27. if it does not, then remove q28 and repeat the test. if it still does not double, then q26 might be faulty.

[spotta]

Nice one. I shall give this a go tonight.
James from willzyx.com (where I got my PCBs & the Transistors) is kindly sending me spares of the four transistors so hopefully I should be up and running soon.

[spotta]

Update

I removed Q25 and tried option 3 but my multimeter was not registering anything. then a pack of 2SC536F & 2SA733P arrived from James so I replaced Q24, Q25 & Q27, I double checked again to clean the Flux from all components around the VCO, but no difference at all. I've ordered a new 2SK30AO so I can replace Q28 next.
I'm now going to remove Q25 again and try the resistor trick.

[spotta]

with the 100k resistor between the pins that go to q27 and q26 and my dmm set to the 2v scale I get
Lwr octave lwr C - 0v
Middle octave lwr C - 0v
High octave lwr C - 0v
Higher octave lwr C - 0.023v
Higher octave high C - 1.123v

[spotta]

Removed Q28, same results. shall I order a new 2SC1583?

[guest]

just to make sure, can you remove C33 as well (this way there is nothing connected to the collector of Q26 but the 100k resistor).

then, if that doesnt do it, can you give me the voltages again on Q26 for both middle low C and higher low C. i just want to be absolutely sure its Q26 before asking you to hunt down a new one. you could also just toss in 2 transistors and see if it works (in place of Q26). they wouldnt need to be matched or anything for a quick test.

[guest]

also, set your multimeter to the mV range for the current measuring tests. what multimeter do you have?

[spotta]

This one http://www.uddle.co.uk/shop/home-and-se ... -pg017-mm/