hartke LH1000

[pontiacpete]

I'm reluctant to even try this one, but.... I'm curious about what it might be.
This amp, the owner says she tried to play through it using an instrument cable for a speaker cable, and now it doesn't work. It apparently powers up, Is there anything, obvious, to look for? I don't have a schematic yet.
Looks like there are 8 large mosfets in the output...

Much thanks in advance
pete

[booj]

could be an internal fuse blown

[pontiacpete]

I've been looking for one, if it's there it's hiding.. ; )

[pontiacpete]

Schematic is here:

[Steve L]

Hartke LH1000

If the amp matches the schematic that you have, those are transistors, not mosfets.
Hartke used power amps with both. You need to know what you have first.
Playing that amp with a shielded cable is not good, there could be a lot of damage done in the power amp.
You might want to look for a lot of shorted parts in the power amp, such as the output devices, before you get deep into it. Then decide if you want to attempt repairing it or maybe just order a new power amp assembly, if that is possible.

Steve

[pontiacpete]

thanks Steve

I now realize that those aren't mosfets. I'm looking through the schematic and so far it looks like the amp at hand.
I'll go ahead probe around the power amp. So far I've only done visual inspection.
I wonder what that board might cost, do you have any idea?

[52 Bill]

I wonder what that board might cost, do you have any idea?

Is the board burned beyond repair? Do you feel it's more cost effective to just replace the entire board rather than repairing it?

[Steve L]

Hartke LH1000

Sorry, I have no idea what a module would cost. I usually fix them myself.

Knowing that you have the transistor version, I would say go ahead and try to fix it, if it is indeed the power amp that is bad.
It is the mosfet versions that give a lot of guys a real hard time.

Steve

[pontiacpete]

Is the board burned beyond repair? Do you feel it's more cost effective to just replace the entire board rather than repairing it?

I'm sure it wouldn't cost much to fix it. The problem I've continually come up against with transistor amps is either I don't have the equipment to pull parts without destroying the PCB, nor do I know an adequate method of testing these components with out ripping them in and out.
I've asked this question before here and didn't get a response, but I will ask it again, -- how does one test transistors in circuit? -- THe only method I no is to take it out put my ohm meter to C and the E and connect the base to the C with a 10k R, if it's good the meter will go from low to high. If I do this to each suspected component without an adequate means of desoldering, the board will take a beating and I'll be in deep like I am with the polytone I'm working on now(a mess). If you are willing to offer any advice i'd be much appreciative.
It looks like I'll be giving it back, though.

Steve ---
If you aren't too deep in CT I could refer this over to you, like as if you don't have work.

thanks
pete

[Steve L]

Hartke LH1000

Pete,

I am on the shore, about 50 minutes away from the NYC line. However, I am fairly well solid with work right now.
Ever since the economy went south repairs have been coming in faster than I can keep up with. I would say that so far this year I have done over twice the repairs I did last year. I guess no one can afford to buy new stuff.

If you really feel the need to refer this customer, send me a PM, otherwise I would prefer to pass on it. Thank you for the kind offer anyway.

As far as testing transistors in the circuit, I only do that when I am looking for obvious shorted or open devices. It can give me a good idea of what kind of time and material it will take so I can give an estimate if needed, or if I might need to quickly order a few parts I might not have.
Sometimes I may have done a few of the same amps in the past and know just where to look as well.

Taking the transistor out as you do is really the best way to test it way since your meter may read other components when testing in circuit. Remember that you need to test all six combinations of leads; C-E, B-C and B-E, forward and reverse.

Steve

[52 Bill]

I don't have that much equipment to desolder parts, only a hand held vacuum sold-a-pult type pump and an iron.

I test transistors in circuit with my meter all the time. The only time I start removing or de-soldering them, is when I think i have found a bad one. Sometimes the circuit will make a transistor test bad, so you have to remove it to check it.

When working on a power amp with a row of outputs, if one is shorted from collector to emitter, they all will test shorted. This is when I will unsolder the emitter leg of one output transistor to test it. If the unsoldered transistor tests ok, then I will unsolder the next transistor's emitter leg, until I find the one that is shorted.

[pontiacpete]

I don't have that much equipment to desolder parts, only a hand held vacuum sold-a-pult type pump and an iron.

I have a solder sucker and de soldering copper braids.

I test transistors in circuit with my meter all the time. The only time I start removing or de-soldering them, is when I think i have found a bad one. Sometimes the circuit will make a transistor test bad, so you have to remove it to check it.

Do you mean you, check for resistance between? 'cause each one of these are showing about 150-190k between the collectors and the emitters, between either and the base it's more.

When working on a power amp with a row of outputs, if one is shorted from collector to emitter, they all will test shorted. This is when I will unsolder the emitter leg of one output transistor to test it. If the unsoldered transistor tests ok, then I will unsolder the next transistor's emitter leg, until I find the one that is shorted.

thanks for this, !!

[pontiacpete]

Pete,

I am on the shore, about 50 minutes away from the NYC line. However, I am fairly well solid with work right now.

Taking the transistor out as you do is really the best way to test it way since your meter may read other components when testing in circuit. Remember that you need to test all six combinations of leads; C-E, B-C and B-E, forward and reverse.

Steve

Nice, I grew up in new london.

thanks Steve

[booj]

If you get ready to test it, make SURE all the ground points are connected. Hartke's won't operate correctly otherwise. Also remember the amps are cooled by forced air with the covers on.(if it has a fan) They'll get hot if run open.

[pontiacpete]

I'm giving the amp back tomorrow, but just out of curiousity:
I have some voltages on the big transistors on top:

Q313,Q315, Q317 and Q319 all have the same:

base = 0.5v
collector= 73v
emitter= 0

Q314,Q316,Q318, and Q320 all have the same:

b = -0.5v
c = -73v
e = 0

are they still good?
anyone?

All fans are running