Colorsound Power Boost - Another issue!!!

The Q3, is this transistor broken? It seems that there is a burned hole.

What's the name of the 3 transistors?

The PCB, hm.... are the pots on an fixed place, or can you rearrange all parts on the board?

Because it is better, if you makes a smaller board with optimized track wiring.

Also the parts, for such tone control preamp they are a bit big.

How look the other boards, which are working right? Are they with the same layout?

Tip:

You can check the basic functionality of the transistor with an Ohm-Meter.

For an NPN: plus (red pin of the meter)  to B and minus to C or E, and the Ohm are low; or minus to B and plus to C or E, and the Ohm are high (MOhm or more).

For an PNP: minus to B and plus to C or E, the Ohms are low.

If you check E to C, a good transistor has an "endless" Ohm (GOhm), otherwise the diodes in the tr. were melted.

Or you can also check the tr. with an diode-meter, or you have a transistortesting on your multimeter.

Gerald

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If that resistor has 15 volts on one side and 0 volts on the other side, then I think you are looking for a short from Q3 collector to ground, not an open circuit.

A fried transistor or a mix-up of EBC cannot short the collector resistor to ground in this circuit.

In a next version, I'd drill mounting holes in the board.

If it hangs in the pedal, held up by the potentioleter pins, I predict that you'll get broken solder joints.

A pedal gets some abuse when used on stage. And your PCB, with the electrolytes, has a decent mass.

@Jan Crumps Only the pots are board mounted, the on/off switch is separate.

@Gerald Schwarz The board is an exact replica of an original. All the parts are as an original 0.5w resistors, and Vishay axial capacitors. Here are some photos of some original powerboosts. All the other boards I've made have been perfect, with no issues. This has clearly got to be a component issue.

The transistors are BC183L the same as an original and are orientated correctly, although I will check to be sure. Pinout is ECB when looking at the transistors from the pin end with the flat on top. The only difference with mine is I've had to mount the pots on the reverse side of  the board as the pot shaft isn't long enough to locate on the board and go through the enclosure. The originals used the pot shaft to mount to the board, where mine use the 3 pins. Also, the originals had the pins bent in the opposite direction to standard angled pot. The originals used custom made pots by Omeg and are not readily available.

I'll have a look

Sorry, the transistors are BC184L... that was a typo

Andy Betts  wrote:

 

@Jan Crumps Only the pots are board mounted, the on/off switch is separate.

@Gerald Schwarz The board is an exact replica of an original. All the parts are as an original 0.5w resistors, and Vishay axial capacitors. Here are some photos of some original powerboosts. All the other boards I've made have been perfect, with no issues. This has clearly got to be a component issue.

 

 

The transistors are BC183L the same as an original and are orientated correctly, although I will check to be sure. Pinout is ECB when looking at the transistors from the pin end with the flat on top. The only difference with mine is I've had to mount the pots on the reverse side of  the board as the pot shaft isn't long enough to locate on the board and go through the enclosure. The originals used the pot shaft to mount to the board, where mine use the 3 pins. Also, the originals had the pins bent in the opposite direction to standard angled pot. The originals used custom made pots by Omeg and are not readily available.

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Thank you for the images.

Please check the polcap on the right side, at the red wire (compare with the original board).

This polcap is wrong rotated. The minus polarity must be on the output-pin (see in the schematics).

The Q3 transistor looks damaged. Is there a hole on top of this transistor?

The 220p cap at the Q2 transistor, is this a ceramic cap with this value? It looks not as such cer_cap.

The treble pot seems not tined right.

Tip:

renumber all parts in the schematics, e.g. R1, R2, R3.... C1, C2, C3,.... T1, T2, T3,..... and so on.

So you can find it easy on the board.

Tip:

This amp is a module. It has an input and an output terminated to GND. So all polcaps must be polarized right to plus (the internal pin is plus, the case is minus)

At the end of the board all outside connected modules also are terminated to GND.

So, then you have two polcaps connected in serial minus-minus as a "bipolar polcap".

Please see the functions of a polcap and bipolar polcap in audio applications, as well the functions of caps types MKT, MKP, MKS, styroflex, ceramic.

Best Regards

Gerald

Andy Betts  wrote:

 

@Jan Crumps Only the pots are board mounted, the on/off switch is separate.

...

 

 

.... The only difference with mine is I've had to mount the pots on the reverse side of  the board as the pot shaft isn't long enough to locate on the board and go through the enclosure. The originals used the pot shaft to mount to the board, where mine use the 3 pins. ...

That's what I try to indicate. The originals used the housing and nut for rigidity. They are made for that.

You are using the 3 solder pins. It will not hold. Guaranteed.

Either the pins will break out of the solder, the solder will break off the pads or the pads will get ripped of the PCB. But it will not mechanically hold.

The polecap is orientated correctly, the polecap is on the V in not the output..... Here is a photo of a board from 1969 which my pedal is based on... It's pretty much Identical. The output polecap is the little on e on the far left of the board.

Below are 2 photos from 2 previous builds I did which worked perfectly.... No change in any component placement.

here is my board design on the left, and the original on the right for comparison. You can see I've marked the "+" signs on my board to prevent incorrect orientation

Yes, thank you.

It was my mistake, I didn't mirror my view (top // bot mirroring) in this area.