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]

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]

Originally Posted by pontiacpete

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]

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]

Originally Posted by 52 Bill

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]

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]

Originally Posted by 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 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]

Originally Posted by Steve L

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

[Phostenix]

That looks right to me. The emitters are the speaker out, so they should have 0 volts with no audio. The bases of the transistors should be about .5v above the emitters, and they are. The collectors are attached to the + and - voltage rails, so those numbers look right, too.

[pontiacpete]

thanks Phostenix,

Q309 and Q310 are doing the same.
Are there any other voltages checks that I could try that might lead to the source of the problem, no sound?

pete

[Enzo]

Well, if you have voltages in the powr amp and no sound, the first question is: does the speaker relay click on a second or two after power is turned on?

With test signal applied, is there strong signal on the output buss? Look for it on the legs of any of the row on 0.22 ohm 5 watt resistors or on the 10 ohm 5 w resistor parallel to the output inductor, or just look at the emitter of one of hte power transistors.. If you have it there, the amp is functioning behind the relay. There does not seem to be a DC problem on the output bus by your readings.

If the relay does not pull in, then we probably have problem with the TA7317 circuit.

[pontiacpete]

"Well, if you have voltages in the powr amp and no sound, the first question is: does the speaker relay click on a second or two after power is turned on?"

not that I am able to hear. Only the sound of fans coming on.

Went on to inject a signal and the scope on the emitter of one of big power transistors and sure enough there is signal.

Does this mean it's either the relay or the SMT/D little digital/mini component board, TA7317?

[Phostenix]

It sounds like the power amp is working, then. Do you have signal on both sides of R334?

Can you get to the relay contacts to check there?

It looks like the ouput signal goes to connector CN501-A after going through the relay. They were kind enough to put the output right next to the +72V rail on that connector, so be careful poking around the connector, but can you get a scope probe into the connector on pin 3 to see if it's there?

[pontiacpete]

I'm having a heck a time locating R334.
I can clearly see R335, but...

I'll try to probe the connector.
thanks

[pontiacpete]

oh. I found R334, it's surrounded by the inductor coil, duh.

There is a signal on the end I can reach.

Now CN501-A ..

[pontiacpete]

no signal on the out of CN501-A .

does this mean the relay is in trouble?

[Phostenix]

If you have signal on both sides of R334, I would suspect the relay, but with only 1 side, we haven't ruled R334 out. Can you see the coil clearly? Make sure it's not physically broken or burned. Wiggle it a little & make sure it's not loose - broken solder joints.

One side of R336 is tied to the relay, so if you've got audio on both sides of R336, we can rule out R334 & that coil.

Can you get to the relay? Is it socketed so that you can pull it out, by chance?

[pontiacpete]

Got a signal on the other side of R334, managed to sneak a clip lead under the coil/resistor. It's a smaller wave with a little notch on the down slop of the the upper peak before 0, but a wave non the less.

the relay is soldered in, not socketed unfortunately.

[Enzo]

If the relay is not energizing in the first place, there is little use in testing its contacts. Follow the schematic. There is voltage on the top of the coil or not, and the coil has continuity or not. D310 is across the coil, so use it as a handy test point for the relay coil.

You have signal on your output bus, good. Is there any DC offset there? Talking about multiple volts, not a few millivolts. The 7317 will detect DC and leave the relay off.

Download a data sheet on the 7317 to help you understand its function.

Samson has used the 7317 in their amps for a long time. In those when I have problems with it, it usually boils down to the small value electrolytics associated with it. Like C317, 318 in this amp.

[pontiacpete]

D310 has -73v on both side of it to ground.

oh, 7317, these caps on the mini board, I presume, do you change them off that board or do you replace the whole board?
Strike that above, found them.

Is there a way I can test these C318, 317? They are buried.

[Enzo]

I have never laid eyes on this amp, so I have zero idea how it is laid out. I check the little caps in the amps by watching their pins with a scope and seeing if they do what a cap would do to any signal there.

Meanwhile...

You have -73v on both ends of D310? We are talking about the diode next to the relay? NEGATIVE 73v?

Actually that is a good clue if it is accurate. If the voltage is really positive, then it is normal for a relay not being turned on by the 7317 chip. However, if it is trylu -73v, then I would look at R346, 3.6k 2w. Upper right on drawing, between relay coil and C350. Is it open or broken free? Is there -73v on one end and +73v on the other?

[pontiacpete]

I will try to find a point from which to check the signal through those caps.

Sorry , my mistake, it has positive 74.7v on both ends of D310(I bet it would help if I gave you the right info)

I looked up the pdf of TA7317P and it says:

"over current detecting circuit, operation at the time of over load, such as a speaker terminal short"

so if one puts an instrument cable, which has, perhaps higher capacitance(?) than a speaker cable, would this IC protect or not protect against that ?

The TA7317 is just a 9 pin op amp it doesn't look like it comes with the mini board that's attached to it.
here's pic of it:

If TA7317 were the problem, do you think this is something I would have to get from hartke,( if I were to fix it)? TA7317 itself only costs about $3.00.

[Enzo]

I think I bought my last 7317s from MCM. You should be able to get them from Samson/Hartke, or from a variety of other suppliers. I have only seen the trhough hole version in equipment. It appears they have now gone to surface mount, so watch the package wherever you order from.

Those caps are not necessarily passing signal, they may be thre to smooth out a signal. I don;t have the circuit in front of me, but sometimes they rectify a signal and filter it to ge an average level.

[pontiacpete]

thanks Enzo
for all the help. If I do decide to continue with this repair I'll get the the 7317 from hartke and replace the 2 related caps you pointed out 317/8.

Most of my repairs have been on old tube amps.
I'm a bit weary of doing work on this amp without a desoldering station of some sort. Do you, in your work, use one and if so what brand?

again thanks to you and to the others who have helped me trace through the problem with this amp, I learned a lot!

Regards
pete

[Enzo]

I keep thinking I should invest in a nice hot air station, but I can;t justify the expense. I have so far been able to do all my sm stuff by hand. Tiny parts can usually be picked off with a solder iron and an Xacto knife point. I find for removing ICs with multipins that "Chip-Quick" works pretty well. I buy it from MCM myself.

Chip Quik: Easy removal of surface mounted devices

My conventional desolder station is a PAce, I am happy with it. A lot of guys seem to like their Hakkos, though I never tried one.

[pontiacpete]

sorry to beat the thread to death, but last week I received the TA7317 from hartke($3.75/p), get a call from the gal who owns says she needs the amp by the 28th. So, me, not feeling so confident about doing thisrepair I tell her it looks like hartke sent me a part that doesn't look at all like the part in the amp(please,if you like, referto pic) and after taking out the board that mounted to the fan box vent there are, to my surprise, a whole set of Q313-7 or so power transistors on the under side. So that means there are a total of 16 power transistors 2SA1837 and they're SNP counter or compliment. One of them on the bottom part of the box had apparently sparked because there's little chard smoke spot on the chassis. This I would think means that the transistor was zapped and no good. I checked for signal on all of the bottom ones and there is a signal.
Anyway I don't know if this is the right part or not, what's in there looks like a mini PCB with SMT parts(please look at picture), this could very well be the exact circuit that is inside the IC they sent me. That's what the TA7317 looks like on the web.
I now even have a way of desoldering , ,, one of the guys on the tekscope forum recommended this

Soldering and desoldering tools

I wish she would just take this amp away.