Powersound Overdriver Colorsound Help

Mcknib

Well-known member
I'd place the jumper on the underside wiring it directly to the resistor solder joint and the transistor socket leg, the emitter connects to both R6 12K and R1 6K8 and as you can see from the schematic and pcb image so obviously check they both have continuity when you have your jumper in place

Your power isn't getting past R2 from your voltage readings so reflow the joint at the north side

Your 5088 link doesn't actually tell us much! We'll just have to assume it's standard pinout

2n5088-transistor-pinout-Equivalent.gif

Get yourself one of these to avoid future transistor pain etc, cheap and does the job

 
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Zduck

Member
Okay, so I took a day off and came back to this thing today. I jumped the collectors of Q1 and Q2 as they had no continuity with the resistors. Now they have continuity and higher voltages. I tested on the out pad of the pcb and we have signal! This is promising. I installed a new footswitch as well that works this time. I tested the pedal and it works-ish. I feel like it’s not quite right. I took a video to help demonstrate the issues.

Volume (top left)
Still fairly quiet overall but louder than before. It reaches unity volume only when it’s fully cranked. I heard these pedals were supposed to VERY loud so I don’t think it’s right.

Gain (top right)
Doesn’t seem to add any/much gain at all. And then when I turn it fully right (9-10 spot) the pedal gets very bassy but I can hear some gain in there.

Bass (bottom left)
Seems to work fine

Treble (bottom right)
Seems to work okay except I notice a slight volume increase when fully cranked to the right?

Also the pedal/switch has an audible “pop” when footswitch engaged. Not sure if that’s just how the original pedal works.

Any things to look for now or general thoughts? Thanks
 

Mcknib

Well-known member
What voltages are you getting on your transistors now

Try audio probing the outputs of the transistors see if you can find where the volume drops off
Check how loud guitar signal is at the collector of Q1 base and collector Q2 and 3

The original 3 knob verson I've read did have huge volume

Switch pop can be improved using a 1M pulldown resistor immediately after the input to ground
 

Zduck

Member
The voltages I’m getting now are:

Q1 (left to right)
2.35, 1.61, 1.05
Q2
10.98, 2.34, 1.71
Q3
9.63, 2.69, 2.06

I checked with the audio probe and the collector of Q3 is the same volume as the input jack. When I probe the “out” pad of the pcb the volume has dropped unless I crank the volume knob fully then it’s the same volume as the input and Q3.

Probing the transistors, Q1 base is same as input but Q1 collector is distorted. Q2 base and collector are distorted as well. But then Q3 base and collector are clear just like the input jack. 🤔
 

Mcknib

Well-known member
Q1 collector is low I'd expect more voltage than that did you reflow R2, Q1 collector is connected to Q2 base so obviously having a knock on effect
 

Zduck

Member
I reflowed R2 and it’s still pretty much the same voltage. Q1 collector is 2.29, the top of R2 is 2.29 and the bottom is 17.75 (vcc). Base of Q2 is same collector of Q1 (2.29).

Curious why the collector of Q2 10.98 but the base of Q3 is only 2.69? Shouldn’t they be the same? Is it because the Q2 collector goes through the eq section and drops voltage before Q3 section brings it up again?
 

Mcknib

Well-known member
Found some voltages from the original on DIYSB don't expect yours to be exactly the same with component tolerances etc but it'll give you an idea

Battery: 18.84V
Q1 C 6.43V B 3.92V E 3.54V
Q2 C 11.53V B 6.44V E 5.82V
Q3 C 10.19V B 2.77V E 2.23V


R2 is definitely 100K from what I can see but appears to be a problem personally I'd check R2 isn't bridged to any nearby components R5, R7 etc then lift the 2.29v side out very carefully and see if you get higher voltage on it

From your voltages VCC is all good you just appear to be dropping 3 or 4 volts too much through R2 you can see for example Q1 collector to Q2 base has the same voltage so looks like it's working just not getting the correct voltage which is what I mean by it having a knock on effect on the rest of the circuit

The voltage on the base of Q3 looks like it would come from the voltage divider R12 and 13 around 3v less a little voltage drop through the resistors

 
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Zduck

Member
I pulled out R2 to be safe and swapped in another 100K. Afterwards I’m getting 1.5V but then I moved the pcb while reading and it jumped up to around 4V Q1 base and collector but is now down around 1.5 to 2 again. Would a loose Q1 transistor inside the socket be causing the inconsistency or maybe I need to jumper all the Q1 legs to resistors in case somethings not connecting right? Seems like there could be bad connection here.
 

Zduck

Member
I answered my own question by measuring voltage on the actual Q1 legs and they match the socket legs and the linked resistors.
I’m getting Q1 left to right:

2.2V, 1.5V, 1V
 

Mcknib

Well-known member
Try another transistor but it seems the voltage you're getting the Q1 side of R2 is low you're getting VCC on one side and it's dropping almost all of it through the resistor did you check to see if R2 is connected to anything it shouldn't have continuity with

Without powering the circuit check resistance from D102 cathode to Q1 collector it should read around 100K ohms (R2 value)
 

Zduck

Member
I checked resistance from D102 to Q1 collector and it’s exactly 100.2K ohms.

I cleaned around the R2 resistor solders and don’t see anything that could be possibly touching it 🤔
 

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Mcknib

Well-known member
With your collector voltage changing whilst you were taking readings try holding the transistor down in the socket see if that does indeed change anything it's just weird getting VCC one side of the resistor and dropping all that voltage through it suggesting a high resistance between the pads but your 100.2K says it's fine, also try pressing R2 see if that affects voltage readings

As you say sounds like a bad connection so prodding and pressing may reveal where it's at

The last time I had a strange fault with a transistor in a socket one of the legs had actually sheared, the other 2 legs and the socket held it in place so when I had it wrong way up it was fine as soon as I put it the other way the leg dropped down disconnecting and it didn't work it had broken in the socket so I couldn't see it

Are your transistors definitely all 5088s?
 

Zduck

Member
With your collector voltage changing whilst you were taking readings try holding the transistor down in the socket see if that does indeed change anything it's just weird getting VCC one side of the resistor and dropping all that voltage through it suggesting a high resistance between the pads but your 100.2K says it's fine, also try pressing R2 see if that affects voltage readings

As you say sounds like a bad connection so prodding and pressing may reveal where it's at

The last time I had a strange fault with a transistor in a socket one of the legs had actually sheared, the other 2 legs and the socket held it in place so when I had it wrong way up it was fine as soon as I put it the other way the leg dropped down disconnecting and it didn't work it had broken in the socket so I couldn't see it

Are your transistors definitely all 5088s?
They are definitely all 5088s. I have a bunch and have even been switching them in now that I have the transistor sockets in there and getting pretty much the same readings.

I think the sockets may possibly be causing the Q1 issues. The Q1 collector is reading 2.2V fairly consistently but if I push the tip of the meter probe into the top of the socket and read the leg there I can get 4.4V from Q1 collector. Maybe pushing the tip into the socket pushes the transistor leg into place a bit better and makes better contact with the socket. What do you suggest I try next? Should I try and pull off the black plastic on the socket to expose the metal socket legs and solder the transistor directly to the socket legs?
 

Mcknib

Well-known member
Those are strange sockets you could try using a cut off component leg to wedge it in better, see if that makes a difference not ideal but ok for testing purposes

Take voltages on the underside solder joints to see if it's a constant 4.4v on Q1 collector

I've never used those type of sockets perhaps your transistors aren't making good contact inside them
 

Zduck

Member
The underside solder joints are reading the same as the transistor legs (Q1 2.2,1.6,1.03) so they must be connecting okay?

So I figured out how I was reading 4V randomly. When I pull out the Q1 transistor and read the Q1 socket or solder joints I get 4V, 3.5V, 013V. I guess when I was pushing in the meter probe it was actually disengaging the transistor legs rather than connecting them better. Isn’t it strange that the transistor is dropping the collector and base voltage and increasing the emitter voltage? I swapped in other 5088s and get the same reading. I’m stumped.
 

Mcknib

Well-known member
R2 is what confuses me you get VCC on one side as you should then low voltage on the other side

What do you get when you remove Q1 from its socket on R2 collector side

The only scenario I've ever had like this was a solder bridge causing a short only when the IC was in socket

I got weird voltages with it in socket and good with it out so naturally thought the IC was toast! not so, it being an active device the same as a transistor it only connected the bridge when the IC was in socket and active in the circuit
 

Zduck

Member
If I remove Q1 I also get 4V on R2 top side and 17.3V on the bottom side of the resistor.

What’s interesting is if I remove all three transistors I get 18.13V on north side of R2 and 18.32V on south (vcc) side..

also to rule out the actual transistors even further, I had some BC109s arrive in the mail today and swapped them in and still got the same Q1 2.3V, 1.6V, 1.03V..
 

Mcknib

Well-known member
Link the actual sockets you're using I'm not familiar with that type

Although I don't think so check the Q1 socket holes don't have any continuity with each other
 
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