Hartke 3500 no output

[nosaj]

hartke_ha3500_power_amplifier_sch.pdfThis is a Hartke 3500 I'd bought the output module from Enzo sometime last year. Been playing ok no issues.

It was hooked up to an ampeg 8x10 cab(4ohm I believe) and now no output.

Looking over the output board q310 looks to have arced through the silpad by the screw.

There is signal coming into the board. but no output. I did a quick run through on the resistors none are open. haven't checked the 5w ones yet.


How bad might this be? Is it possible it could've blown all the outputs?
None of the power transistors test shorted BC. 2sa1943 s and ktc5200 are the output transistors. I do have a few that test from the heatsink screw to collector about 2megs(this issue addressed with new mica). The others test OL.. I'll take thos out of circuit to test.
Thanks,
nosaj

[The Dude]

Check the transistors with the diode check function. No need to remove them unless you find a short -then remove to verify. Resistance checks there don't tell the whole story. Is there any DC offset out of the amp? Check on the input side of the relay- it might not be engaged to connect to the speaker jacks. Can you hear the relay click and/or is there voltage across the relay coil (measure across D310)? The amp may be sensing an offset problem and not engaging the relay.

[nosaj]

Check the transistors with the diode check function. No need to remove them unless you find a short -then remove to verify. Resistance checks there don't tell the whole story. Is there any DC offset out of the amp? Check on the input side of the relay- it might not be engaged to connect to the speaker jacks. Can you hear the relay click and/or is there voltage across the relay coil (measure across D310)? The amp may be sensing an offset problem and not engaging the relay.

Question here testing with the diode check function what does a short look like? My meter gives me OL or the somewhere around .667.
DC on output no load is 5.9mvdc then relay clicks on then shows 1mvdc.
measuring across D310 shows about 29.70vdc.

Q310 When replaced show under a volt an any of the 3 legs. So my belief is something before it died.
Q309 has I believe 80 something volts on the collector. As do q313,315, 317, 319 and q314,316,318,320.
The base and Emitters have a low voltage on them. Somewhere someone had told me that if the voltage was the same across 2 or 3 legs it would be a shorted transistor. Is that a logical assumption or should I deepsix that notion?

Thanks,
Nosaj
Hopefully I answered all your questions

[Enzo]

What does a short look like? TOuch your probes together and find out.

[nosaj]

What does a short look like? TOuch your probes together and find out.

Ok none of the outputs are shorted. So the problem will be before q310.
So I have B- on Q314, 316, 318, 320. Looking at the schematic and this is just me kinda of guessing but It looks like B- is going from right to left While Signal(AC goes left to right), So I'm thinking I need to check for B- on R314, C312, R321, and D306 cause that's whats nearby.

Ok on those 4 items about half a volt dc on either side.
Ok I'm thinking q308 is next to check. BTW way what is TH302(a fusible resistor?)

Thanks,

Nosaj

[Enzo]

If you had blown transistors, you'd probably also have blown fuses. If your collectors shorrt to frame, you blow fuses.

Is the speaker relay clicking on a couple seconds after power up? With signal applied, and power, is there signal on the ballast resistors? They are a convenient point to check for signal before the relay.

[nosaj]

If you had blown transistors, you'd probably also have blown fuses. If your collectors shorrt to frame, you blow fuses.

Is the speaker relay clicking on a couple seconds after power up? With signal applied, and power, is there signal on the ballast resistors? They are a convenient point to check for signal before the relay.

Yes relay clicks.
What are ballast resistors? are they the .47 5watt resistors?

Thanks,
nosaj

[Enzo]

Yes.


OK, so the output is no offset or the relay would stay off.

is signal even getting to the power amp input connector? If so, does it get to the VAS stage?

[nosaj]

Yes.


OK, so the output is no offset or the relay would stay off.

is signal even getting to the power amp input connector? If so, does it get to the VAS stage?

What is the VAS stage?
Will verify signal to the power amp Connector AN101 I believe.

Thanks,
nosaj

[Enzo]

Signal input... looks like they didn't give teh differential transistor a number, but is ther signal at R302? How about the collector Q305? Did you find signal on the ballasts? Or instead of them, on the coil with R334.

[Jazz P Bass]

What is the VAS stage?

VAS is the Voltage Amplification Stage.

Among other things, it boosts the signal coming out of the differential pair.

[nosaj]

Signal input... looks like they didn't give teh differential transistor a number, but is ther signal at R302? How about the collector Q305? Did you find signal on the ballasts? Or instead of them, on the coil with R334.

No signal at r302, q305 or the coil. But there is signal where it enters the powerboard at AN101/
I'll check at c302 for signal
Thanks,
nosaj

[nosaj]

No signal at r302, q305 or the coil. But there is signal where it enters the powerboard at AN101/
I'll check at c302 for signal
Thanks,
nosaj

Looks like the differential transistor on the board is labeled q301 and 3067. I have signal on emitter and collector of q301 which is the left transistor in the dotted box. On it it says k120 c3200. There is 80volts on the collector and less than half a volt on emitter and base.
The way it is on the schematic I should have signal on both emitters if I have it on one. Right?

Thanks,
nosaj

[nosaj]

Looks like the differential transistor on the board is labeled q301 and 3067. I have signal on emitter and collector of q301 which is the left transistor in the dotted box. On it it says k120 c3200. There is 80volts on the collector and less than half a volt on emitter and base.
The way it is on the schematic I should have signal on both emitters if I have it on one. Right?

Thanks,
nosaj

I have a 2n2222 that looks like it should be a compatible replacement.

Nosaj

[J M Fahey]

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