Big Muff Pi help, no effect

[pontiacpete]

I'm working on one of these, the closest schematic I can find is below.
The transistors are STP 87-103, or so it is written on their bodies. One of them had a broken leg, so
I tried replacing it with a 2N5089, with no luck. Is this a suitable replacement?

Thanks for any help!
pete

[Jazz P Bass]

What is the pinout of the broken transistor, as there are three different arraignments for the transistor pins.

http://www.armory.com/~rstevew/Publi...anspinouts.htm

2n5089

BC549

http://www.kitrae.net/music/Big_Muff...eaks_Page.html

[pontiacpete]

Is the STP.. ... the same as BC549? I have some of those

I am using the pin out for the 2n5089, (it's Q3 that was broken) It's seems to be connected correctly. There's something like 4v on the collector. 0v on the emitter and .6v on the base

[Jazz P Bass]

2N5089 & BC549 have an opposite pinout.

Check the pinout orientation on one of the other transistors. (they should all be the same)

So, do you have a signal on the base?

[J M Fahey]

Agree and add: an "upside down" transistor is still NPN and will still show 0.6V BC , now wired BE .
It will still work as a transistor, sort of, only current gain Hfe will drastically drop from typical 100-500 to useless 2-3 or so.

If your multimeter has an Hfe tester socket, measure transistor both ways, the position reading high gain applies, read leg labels straight from what's printed on multimeter face.

I do it all the time: my regular multipurpose transistors are BC549/559 or BC550/560 but when higher voltage is needed I use 2N5401/5551 which *should* have same pinout ... alas it depends on manufacturer so I always check them as mentioned above just in case, the 10 seconds it takes are well worth the save headaches later.

[pontiacpete]

Ok now it's passing signal and working somewhat. It's not nearly as loud as I would think it should be. In fact it has less gain than the unaffected signal.
Could it be that Q3 is in backwards? This is weird. When turning the on/off slider switch(is that what it is?) the volume is really low with everything maxed and comes up gradually but never gets as loud as I've heard these before
I changed a couple of the electrolytics C4,5 and 6 around Q3 and Q4.

[52 Bill]

When turning the on/off slider switch(is that what it is?) the volume is really low with everything maxed and comes up gradually but never gets as loud as I've heard these before

Yes, the new transistor could be installed wrong.

What switch are you talking about, a power switch or a tone bypass switch?

[pontiacpete]

I'm talking about the slide switch, not the stomp switch. The enclosure is worn. The only thing it says is 'off'. The unit came to me with the battery red lead connected to one lug of the slide switch and the other of the switch is connected to 33k 10k and 33k resistors. These seems to be an on/off to me, maybe redundant since it has the stomp.
I ended up trying a BC549. Same results. I think I've installing them correctly . The emitted has a 120R resistor to ground.
The collector has the higher voltage and the base is connected to the wiper of the sustain pot thru a 2.7k resistor and a 1uf cap.

[52 Bill]

I'm talking about the slide switch, not the stomp switch. The enclosure is worn. The only thing it says is 'off'. The unit came to me with the battery red lead connected to one lug of the slide switch and the other of the switch is connected to 33k 10k and 33k resistors. These seems to be an on/off to me, maybe redundant since it has the stomp.

It sounds like it is an early one, that is the battery on/off switch. Later ones had a tone control bypass slide switch. The stomp switch just turns on and off the effect not the battery.

[pontiacpete]

yes, it's an old one, and a lot of work has been to it. It had a number of jumper wires bypassing broken traces. I removed them and restored the traces by clearing off the copper and soldering wire to them. The first picture you can see the 2n5089 in place with the flat side facing down. That is now changed to the BC549 with flat side up.
At this point I might change out the rest of the electrolytics and continue tracing through all the connections.

[pontiacpete]

Got it working! One of the electrolytics was bad, it had a big hole in it on the underside facing the board.
Thanks for all the help! Much appreciated!

pete

[Jazz P Bass]

Nice work.

Thanks for the update.

[doctor]

For your information.
The 2N5088 are used in the genuine device.