Hartke 3500 no output...photo enclosed

[Garydean]

No output and found this mess around the relay and dripping onto the box. Any ideas? I jumped the send and return....nothing. Fan kicks right on.

thanks,
Gary

[Enzo]

Looks like a drink spill to me. That didn't come out of anything on that board.

OK, it is not blowing fuses, right? Power it up. Make sure the inpt connector is plugged in as well as that power connector. Does the relay click in after a few seconds? Prolly not.


Are the main power rails getting to the module? Module meaning that whole thing you are holding. The center legs of each power transistor down each side will be one rail or the other.

Next to the relay is a large open wire inductor. Is there substantial DC there with respect to ground? If so, the relay won't let the speakers come on line.

[Garydean]

Hi Enzo.

Fuses are not blowing. Relay kicks in after a few seconds. + and - rails read 81.5 and -81.5 respectively. Hardly any DC on the inductor, almost nil All OP Amps are reading close to -15 or 15 at the corners..

Gary

[Enzo]

OK, so it is ready to work. APply a signal to the preamp input and see if it makes it to the input conector of the power module. Leave the input connector in place because the input stages of the power midule rely on it for their ground. But you can still inject some signal, at this point even hum, and see if it comes out the speaker.

Also, monitor that coil of wire with a scope or AC meter. Is signal present there? That coil is the output bus just before the relay. If signal is there, the amp is running and either the relay is bad or there is no continuity to the speaker jacks. With powr ON, check continuity from that coil to the tip of the speaker jacks.

PLug a signal into the power amp in jack or the effects return, whichever it has. Any output? APlpy a signal up front and sent the preamp out and/or the effects send to another amplifier. Anything? That would be the preamp out. Spin the tube/solid state knob, any effect?

Are the lights on on the graphic sliders? They must be enabled by the EQ IN switch on the panel.

I'd say the drinkie spill probably is not involved..

[Garydean]

I'm getting a signal on the power module at Q301 base. No signal at the coil. No signal at Q302. Yes signal at C303. Should I think Q302 starts the problem area? I should start removing components from there on out and test them? Flipping the power board involves removing ALL the power transistors? Unscrew the pt's or desolder the legs?

thank you!!!

[Enzo]

Nah, don't remove anything. To flip the PA board, just remove the screws through the transistors and spread them slightly. Now the board comes free with the transistors sticking into space, but still intact.

But leave it together for now.

YOu got signal to it, good.

VR301 is the output offset adjust. With NO LOAD, watch DC voltage on the output and twiddle VR301. Does the oputput DC level move around with it? If so, most of the amp works. If not, the DC path is faulty. Monitor at the coil in case our messing trips the relay.

The four outputs on each side are parallel, so testing one tests them all on a side. Set your meter to diode test and check them. I bet they are OK, or you'd be blowing fuses.

Now the rest of the PA only has 12 transistors, and two of those are in Q301. Just run down the board and test evry one for junction drops. REmember Q303 and Q306 are wired as diodes, so don't think they are shorted when base and collectors are wired together. Likewise diodes, there's only about 8 of them.

Since the relay kicks in, we can assume everything is OK to the right of the output transistors in the schematic.

I wouldn't expect signal at Q302 anyway, it just controls the current for the diffy pair Q301, along with its buddy Q303.

Got signal at Q305?

[Garydean]

Thanks Enzo,
I jumped the gun as this sucker has taken over my bench. I lifted R311 and
R312 as they had very odd readings in circuit. R311 has drifted off the chart and R312 tested fine. (are they 1/4 watt resistors BTW?) I did test a few of the small transistors and they looked good. I'm going to replace R311 and put it back together and try your test procedure. My SS skills are not great and I hate pulling the trigger with the shotgun method. But I really don't have much time into it so far.

All 8 outputs test fine. I popped the 2 larger diodes as well..they measure good.

Thanks again,

Gary

[Enzo]

Just test the transistors in circuit, I never meant to imply removing them. SOme junctions measure low, so look at the schematic and see what parallel resistances might be responsible. Without removing them from the board, you can test every transistor on the baord in a couple minutes.

[Garydean]

Hey Enzo,
I replaced the 10k resistor..... the amp is working. What is the factory setting for the output DC level?

Thanks for the lesson.

Gary

[Enzo]

With no load, watch the output. Twiddle the offset trim for least DC voltage - the spec is as close to zero as you can get. And don't sweat a couple millivolts.

UNless you twiddled it, the bias is probably OK, but it adjusts like any solid state amp bias.