SWR Workingman 15

[bnwbass]

Can someone who has a workingman 15 be so kind to look on the power board and give the resistor color code for the posistion in the the attached file.
Thx
Bw

[Jazz P Bass]

Are you sure that it was populated?
It appears to be in parallel with the other one in the circle.
How about a bottom pick?
Circle it again, that was nice.

[bnwbass]

Hi Jazz P Bass,

Well I removed the resistor from the board,(the pic shows it missing) it must of got hot and the color code is faded so I am not sure what the value is and this what I am looking for. I have the schematics but there is no PCB layout drawing according to SWR/fender folks. If I trace per the schematic it looks like R36 270 Ώ 2w but the resistor I pulled out is ¼ w so I am not sure and would like to verify against someone else's board.

thx
bw

[Jazz P Bass]

Uhm.
Can you post the schematic for all to see?

[bnwbass]

Workingman's 12-15-2004 Power and Pre Amp Rev 01.pdf

[Jazz P Bass]

O/k.
Now, a picture of the bottom view would help.

[bnwbass]

Resistor position outlined in yellow
thx
bw

[Jazz P Bass]

Can you tell what the value is of the resistor that is there on the board. (in the circle)
I,m having a hard time with this one.
The second picture is nice & clear.
The first one is really fuzzy.

[Jazz P Bass]

As far as I can tell, without more info, the circuit consists of Q3 & Q5.
Q3 is the high side driver & Q5 is the bias transistor.
It also appears that you may have another burnt resistor.
Directly to the left of the resistor in question are three electolytic capacitors.
Right below them is a resistor that looks toasted.
At any rate, if the bias circuit is suspect, you may have more problems.
I would check the output transistors (Q4 & Q10) & their drivers (Q3 & Q4) for shorts.
The bias transistor (Q5) should also be checked.
If any transistors are found shorted, then you must check the associated resistors.
(something took out the resistors, they did not just burn up for no reason)

[Enzo]

Resistors do not burn up on their own, it is always caused by something else failing. Usually a semiconductor.


Man, I tell 'ya.. Looks like R23 maybe? The smaller resistor just above it would be R24. There is a row of three radial e-caps just left of it, and the closest one would be C11? If so, that cap wouldbe 47uf/63v. Yep, resistor and diode in series off the other end.

R23, my final answer, Regis.

[bnwbass]

Thanks guys for looking, the resistor I pulled measures out at 2.7K which is the R23. The print says this is a 1W resistor but what I pulled out is 1/4W.
I will check the other transistors around it but Q10,4,3 are all OK.
see attached

[Jazz P Bass]

That is NOT a 1/4 watt resistor.
Metal film, 1 watt is my thinking.

[bnwbass]

Well it's not any different than all of the other 1/4w 5% res on this board, as per the schematic are 1/4 unless noted. There are (2) 2W metal resistors and they look very different that the rest, so I don't think the one I pulled is metal.

[Enzo]

No kidding, I got R23 right? Believe me that took some serious back-and-forthing with the photos and schematic.

[bnwbass]

Thanks for your time Enzo... I am going to replace with new parts. I noticed in another post you may have a pdf of swr 550x main power amp schematic. If so could you send me a PM with the file? I am working on a unit that blew all (6) sanken 2sc3264 output driver devices.

thx..again

bw