SWR Workingman's 15- Voltages- DC on Speaker

[Enzo]

PNP. Base sits 10v more positive than emitter. Reverse biased then.

[BStringThumper]

Thank you both for taking a look at the numbers again. I will double check those voltage again with my Fluke. All of these voltages were taken on the bulb limiter. I found an older schematic, not for this unit, and it showed rail voltages at -+ 59V. I will post new numbers shortly.

[DrGonz78]

One question I have following along with this thread is about what is written on the schematic. For Q3 (2SC4382) is has PNP written above it, but that transistor is an NPN. So what transistor is in Q3 right now and is it a 4382? Probably nothing but misprinting pnp for an npn but just gotta make sure.

https://www.digikey.com/product-deta...382-ND/3929372

Edit: perhaps Glebert already pointed this out and it is not an issue. Just someone wrote pnp on the original reference schematic...

I think Q4 too. Also some of the transistor types are labeled wrong (NPN vs PNP), just don't want you to confuse yourself.

[glebert]

PNP. Base sits 10v more positive than emitter. Reverse biased then.

There is current flowing through R35 (about 0.3mA) to cause that 20V drop, so it is either going into the base of Q6 or C16 is leaking it to ground. Usually for reversed biased transistor I expect zero current, but don't know if 0.3mA can happen due to some leakage.

[glebert]

One question I have following along with this thread is about what is written on the schematic. For Q3 (2SC4382) is has PNP written above it, but that transistor is an NPN. So what transistor is in Q3 right now and is it a 4382? Probably nothing but misprinting pnp for an npn but just gotta make sure.

https://www.digikey.com/product-deta...382-ND/3929372

Edit: perhaps Glebert already pointed this out and it is not an issue. Just someone wrote pnp on the original reference schematic...

Yes, I had mentioned this up in #6.

[Enzo]

If C16 is leaking then a drop would appear across R34. Is it?

Or Q6 is defective.

[BStringThumper]

All voltages with the Fluke moved just a little bit from where they were before. I appreciate any suggestions on what to check next.

[BStringThumper]

I am so sorry for mislabeling the transistors. Here is the new sheet. No voltage drop across R34. Thanks again to everyone for helping me out.

[BStringThumper]

Good morning,

I really am sorry for not having the NPN and PNP written correctly on the sheet. I want this post to be helpful for anybody that encounters this same problem. It wasn't helpful that I made a mistake. I appreciate all the help I can get. I don't know what else to check. I even powered it up with a 4 ohm dummy load hoping I'd feel something getting warm/hot, nothing, the speaker jack was reading 6.65 volts dc. But I still had the bulb limiter in line. Any thoughts, please?

[g1]

With limiter and load, power up without the load, then attach load without turning off the power.
Some amps will not turn on properly on the bulb limiter while load attached, so you need to attach the load after power up.

edit: this is assuming you have already got to the point of no DC on output with no load.
If you are not at that point yet, you must first eliminate DC on output unloaded.

[Jazz P Bass]

Looking at your voltages the first item that jumps out is the Base voltage of Q3 being so high.
So either it is faulty or Q4 is (or both).

[BStringThumper]

Hi, g1 & Jazz- thanks for your input. g1, I still have 31Vdc on speaker jack with no load. Jazz, I replaced Q3 (2SC4382) with a new unit. I don't have another Q4 (2SC3264) to swap. Diode test is the same for Q4 & Q10. No changes to voltages from last uploaded schematic. Any other thoughts, please?

[glebert]

Any other thoughts, please?

I think Q6 needs to be scrutinized, based on the fact that current appears to be flowing into its base (because of voltage drop across R35) despite it being reversed biased. See discussion in #13-15 and #19-21. Of course if R35 is actually not OK or there is a broken solder joint there that could also explain the voltages seen. Even if Q6 is bad though it still looks like current is flowing into all three pins (which is impossible).

[BStringThumper]

Hi, Glebert- I will replace Q6 and inspect R35 and reflow the joints. I'll reread the mentioned posts. I'll be back shortly. Thanks!

[Jazz P Bass]

My next step, seeing that Q3 has been replaced , would be Q2.
Why is the Collector & Emitter voltage the same?
A PNP transistor with a high voltage on the Base should have very low voltage on the Emitter.