Hartke 3500 no output

[The Dude]

Did you ever check for signal on the transistor side of C302 or the base of Q301?

Edit: Simulpost.........Sure, while I'm typing and asking if you found signal at some point, our resident solid state genius says to not worry about tracing signal, yet.

[nosaj]

I think you are testing these "as if it were a tube amp" with all this "checking for signal (voltage) inside".
But SS power amps are jusr a BIG Operational Amplifier, DC coupled *everywhere* so I suggest not feeding it an AC signal (for now) and measuring citical DC voltages.
IF you get them all right, then amplifying AC audio signals is (relatively) simple.
So I ask somebody to post the proper schematic so we all speak about the same, and Iīll post a series of DC tests which will tell us a lot once answered.

OK, now I see a schematic pdf on the very first post.
Iīve extracted the power amp as a .png so itīs easily editable, and will show some test point numbers in circles.
The ones with only one red "arm" mean that voltage is measured with red probe there , and black probe to ground (say, a rail voltage); the ones showing red and black mean probes should go where indicated (across a resistor, diode, or BE junction).

Iīll post it "raw" first to check whether it applies and matches your PCB , if so will add the test points and then you will add the voltages you find.

Sorry for the very detailed and "condescending" instructions, he he, , we seem to have been visited by some people with bad attitude and self respect problems lately.
Oh well.

Almost forgot: here it is:
Letīs keep track of versions (calling them 01 , 02, etc.)
Sorry, again a condescending answer

Straight and to the point. I'll print it out and check tomorrow after work, just got in from towing a vehical.

Thanks so much,
Nosaj

[nosaj]

Did you ever check for signal on the transistor side of C302 or the base of Q301?

Edit: Simulpost.........Sure, while I'm typing and asking if you found signal at some point, our resident solid state genius says to not worry about tracing signal, yet.

Yes there was signal at the base and Emitter of q301, the other transistor 3067 is what it says on the PC board.

nosaj

[nosaj]

I think you are testing these "as if it were a tube amp" with all this "checking for signal (voltage) inside".
But SS power amps are jusr a BIG Operational Amplifier, DC coupled *everywhere* so I suggest not feeding it an AC signal (for now) and measuring citical DC voltages.
IF you get them all right, then amplifying AC audio signals is (relatively) simple.
So I ask somebody to post the proper schematic so we all speak about the same, and Iīll post a series of DC tests which will tell us a lot once answered.

OK, now I see a schematic pdf on the very first post.
Iīve extracted the power amp as a .png so itīs easily editable, and will show some test point numbers in circles.
The ones with only one red "arm" mean that voltage is measured with red probe there , and black probe to ground (say, a rail voltage); the ones showing red and black mean probes should go where indicated (across a resistor, diode, or BE junction).

Iīll post it "raw" first to check whether it applies and matches your PCB , if so will add the test points and then you will add the voltages you find.

Sorry for the very detailed and "condescending" instructions, he he, , we seem to have been visited by some people with bad attitude and self respect problems lately.
Oh well.

Almost forgot: here it is:
Letīs keep track of versions (calling them 01 , 02, etc.)
Sorry, again a condescending answer

Hey there Juan, this schematic works for me.

nosaj

[nosaj]

Ok here's one with some voltages. On the outputs I only listed the first 2 because the voltages are the same for each set.

Thanks,
nosaj

Juan I tried to use your picture but it was so incredibly small when I tried to edit it.
I used skitch to edit it.

[The Dude]

There are some things "goofy" there. I can't read the transistor numbers on my end. The pic is a bit blurry. So I'll try by location. At the top and in the middle of the drawing, you show 79V at one transistor collector and then .18V on the collector of the output transistors. They are the same point, so one reading must be wrong, or you have a burnt trace or bad jumper somewhere. Another problem I see at first glance is that the NPN outputs have 79V on the base and .001V on the emitters. This is not possible unless the transistors are open B-E. Either that, or you left out some decimal points or something. Or, maybe you have the B and C readings written backwards on the drawing?

[nosaj]

There are some things "goofy" there. I can't read the transistor numbers on my end. The pic is a bit blurry. So I'll try by location. At the top and in the middle of the drawing, you show 79V at one transistor collector and then .18V on the collector of the output transistors. They are the same point, so one reading must be wrong, or you have a burnt trace or bad jumper somewhere. Another problem I see at first glance is that the NPN outputs have 79V on the base and .001V on the emitters. This is not possible unless the transistors are open B-E. Either that, or you left out some decimal points or something. Or, maybe you have the B and C readings written backwards on the drawing?

You said burnt trace and I looked and saw one q314 on collector going to a jumper. Whats the best method to repair a burnt trace as I've never had one before?

Thanks a bunch,
nosaj

[The Dude]

Depending on the size of the trace:
1) If it's larger, scrape the coating and solder a jumper wire across the break.
2) If it's smaller, I usually track down where the trace goes and solder a jumper wire from point to point where there is a larger solder pad or through hole.

[nosaj]

You said burnt trace and I looked and saw one q314 on collector going to a jumper. Whats the best method to repair a burnt trace as I've never had one before?

Thanks a bunch,
nosaj

Ok. I cleaned the burnt section off as much as possible. Took a 5watt resistor, snipped a little bit off a lead and tac'ed it in and soldered it in. Put power amp back together tested the bass through it. We got it back. I didnot have anymore silpads for the transistor that arced. So I put a little heat shrink on the screw that holds it down. and I took the old silpad and laid it on a t0-3 silpad that I had which was big enough to cut what I need it out. So tomorrow I completely close amp up and burn it in. Any suggestion on a recommended burn in time?

Thanks guys one of these days you'll learn me some smarts.

nosaj

[J M Fahey]

COOL.
I am very busy, only now could get into the Forum again, happy you solved it and it was a team effort

In any case, see that in this kind of amps, checking DC gets you way faster to the solution or at least to the main suspect area.

Of course, after DC voltages are as expected, by all means inject some audio and check you get full output voltage and prooper waveforms, both without and with a load

EDIT: about the schematic .png on post ·15, just checked and the full image is therem some 1700x700 something pixels, larger than most screens.

You must right click on it and "open link on new tab" or download *link* (not the thumbnail itself) to, say, desktop and open it with any graphics software to be able to edit it; **maybe** if you just order "see/show image" without furher ado you see the enlarged thumbnail, which of course is tiny and blurry.
Just to be considered for the next riddle, of course.

[The Dude]

Glad you got it, Jason! This just illustrates why it's a better idea to take a methodical approach to repairs and actually troubleshoot something rather than shotgun it. You could have thrown parts at the amp all day and it would not have made a difference.

[nosaj]

Glad you got it, Jason! This just illustrates why it's a better idea to take a methodical approach to repairs and actually troubleshoot something rather than shotgun it. You could have thrown parts at the amp all day and it would not have made a difference.

In the post #1 once I swapped Q310 I think the one that arced to the heat sink, when the voltages were still off I should have looked at the other side of the pc board( but I really didn't want to take it apart) Could've saved myself some time.
But either way The group effort is what I really appreciate here, it's the kind of mentoring I cannot find locally.
Thank you for all your time and effort. I wish other newcomers could appreciate the community that is here.

Nosaj

[The Dude]

FWIW: That last post wasn't directed at you specifically. It was a generalization.

[nosaj]

FWIW: That last post wasn't directed at you specifically. It was a generalization.

Well I've been guilty of it before. An repetition(hearing stuff over) never hurts, eventually it might sink in.

nosaj

[J M Fahey]

Sorry but I have nothing.
I downloded the schematic, added some red and blue arrows suggesting test points and uploaded it.
And erased my side of the deal, trusting Forum server.
Now I see only the thumbnail is available, although Forum "memory" remembers that itīs 120 something kB .
Weird but not surprising considering the Forum stored file problems.

But basically:

1) all bipolar transistors work with around 0.65V Base to emitter; positive in NPN and negative in PNP.
So measure all; if you find, say, +3 or +5 or +15V BE in an NPN transistor, then BE is internally open.
If less than 0.4V, itīs unbiased so itīs OFF, check why itīs not receiving its turn on signal.
If 0 then itīs probably shorted or the path leading to that base is open.
If negative, then something is grossly wrong.
Same for PNP but invert expected polarity.

2) All NPN transistors need Collector more positive than emitter to pass current, if not see who feeds it and why voltage is not reaching transistor.
If 0 then itīs probably shorted CE *or* base is being fed a ton or current (why?) .
Again PNP is same but with opposite polarity.

So in a nutshell: we do NOT pull all parts for measurement: itīs slow, can damage parts, *will* damage PCB and best case that covers only *half* the problem.
We DO measure voltages, inject and follow signal, and that LEADS us to the bad parts area.