Help with console solo circuit

[angelothewolf]

hi,
solo is always on, but with the led a little dim all components are ok etcept for the transistors, the schem shows a BC212L and i got 2n4402, can someone explain me a little bit how this thing works please?

[g1]

The BC212 and the 2N4402 have different pin-out, did you adjust their placement accordingly?

[angelothewolf]

The BC212 and the 2N4402 have different pin-out, did you adjust their placement accordingly?

yes,
im prety shure is a transistor problem, but i couldnt find any equivalent to work

[Enzo]

How many things can turn on the solo? I am assuming this is a mixer, it would be great if we knew make and model.

usually there is a solo bus, and each channel and often other things like sub groups has its own solo button. All those buttons in parallel. If I see a hung solo light, my first 24 suspects are the channel push buttons themselves. One leaky one and the light is stuck.

CON5 pin 3 would be the solo bus. what voltage appears there?

If CON5-3 is open, then R105 pulls Q1 on by its base. With Q1 on, its collector pulls Q2 off. That opens the circuit to the LED and relay. If I pull CON5-3 positive enough to turn off Q1, then the open Q1 allows R104 to pull Q2 on. That causes current to flow through Q2, thus energizing the relay and lighting the LED. That is how the circuit works.

[angelothewolf]

Thank you very much!
it is a MTA series 924 console, im with no channel strips connected. just master and fx returns modules, also Q2 has a parallel transistor (2N4402) on the solder side of the board, that does not apear on schem.
gonna take some measurements...

[Enzo]

Um... I can think of no reason on earth that there would be two small transistors in parallel, other than someone attempting repairs and no knowing what they were doing.

Nonetheless, it is a circuit, like any other circuit. It has an in and an out, and signal flow, even if signal is simple off/on. So what is happening at CON5-3? We need to figure out of the circuit itself is not working, or if the circuit is working as it should, and the problem is something is turning the circuit on at CON5-3.

[angelothewolf]

Um... I can think of no reason on earth that there would be two small transistors in parallel, other than someone attempting repairs and no knowing what they were doing.

Nonetheless, it is a circuit, like any other circuit. It has an in and an out, and signal flow, even if signal is simple off/on. So what is happening at CON5-3? We need to figure out of the circuit itself is not working, or if the circuit is working as it should, and the problem is something is turning the circuit on at CON5-3.

well, the solo dc bus is working properly, i have nothing coming through it (CON5-3). Just master module connected, and still have +18vdc on the base of Q1.
in the master module i have aux masters and oscillator, going to solo dc bus too. If i pull the transistors all the voltages apears right.

[Enzo]

+18 on the base of Q1? Where's that come from? Is R105 open? is there -18 on the south end of R105?

Pick some solo button on that master section, press it on and off. Does the voltage at base of Q1 toggle or not? if you get it to toggle, then does the voltage toggle at the base of Q2. it should be the reverse of base Q1. The on/off control voltage is a signal, so treat it as one. If this were an amplifier, and nothing left the output, we'd put a signal in (button on and off) and trace it along the "signal path".

Does your schematic identify the transistor types. it says nothing next to the parts, but often there is a notes section somewhere on the page saying all PNP are such and such unless noted otherwise. or something like that. Since the unit has had repair attempted already, we need to know just what real transistors belong there. You mentioned BC212, are BOTH supposed to be that? As G1 pointed out, 2Nxxxx and BCxxx have different pinouts. Transistors may be equivalent, but have to twist the legs around to replace one another.

[angelothewolf]

the schematics came with a parts list, original transistors are both BC212L. i found some BC212 and put those in circuit now the led is not dim. i have +5vdc on base of Q1, and when i press a aux solo that 5vdc becomes +18vdc. C49 is not fitted in the board...

[angelothewolf]

ok, i was confusing C49 with C44. i found C49 (a 2u2 poly) close to the aux solo switches and it was short! replace it and all the voltages are perfect without the transistors fitted in, the voltage at the base of Q1 toggles between +/-18VDC, but when i fit Q1, the base becomes +18vdc and doesnt toggle anymore. I think im not getting the pinouts wright, i found 3 diferent pinout for the bc212, i try a couple of BC560, with same results. Any thoughts?

thanks!

[g1]

Here is the pinout for BC212 :


Now follow the schematic to see where each leg goes, for Q1, base goes to C49/R105 junction, emitter goes to C49/D1 junction, collector goes to R104.

[angelothewolf]

Here is the pinout for BC212 :
[ATTACH=CONFIG]36258[/ATTACH]

Now follow the schematic to see where each leg goes, for Q1, base goes to C49/R105 junction, emitter goes to C49/D1 junction, collector goes to R104.

That is what i did, but is not working. what is c49 doing on the circuit?