Be gentle - first time poster with a problem with a Proceed amp

[jacketfan]

I was referred here from a post on AVS. As I look around this forum, I can tell I am out of my league. But I have a problem that hopefully you guys can help me out with.

I have a Proceed HPA 3 that has died. About 5 years ago I had a similar card failure and sent it off to be repaired. The repair was completed and all was well until this weekend. Had the same failure as before. The unit powers up for a second then goes into self protect mode. I isolated the bad board down to the center channel.



Before I do anything else I would like to try and fix this myself.
I have also checked all of the resistors and believe they are good. Except for two components that look like resistors to me, especially because of the way they are marked. One is black, the other white.

I have taken some pictures of the bad board and of the board that was repaired earlier. If I visually compare the two boards, it is apparent that the repair shop simply added a new component over the old one. The shop used the same replacement component for both of the failed components. It is labeled:

TRC LF
8k 66 1%
The pictures below show the old versus new for the two components.

The white component is a:
CP-5 Mexico 9913
1.8K OHM 5% Dale 5W

And the black one is a:
IRC
2k74 TO
9849

Repaired board:



Bad Board



Repaired white component



Repaired black comonent




What I would like to do is get some help in determining what the correct replacement parts are and where to order them.

I will then use my meager soldering skills and try to make the same repair as the previous repair and see if I can get this amp working again.

Am I crazy to try this, or should I turn this amp into a boat anchor?

I do not claim to be electronically inclined, but want to try and fix this problem. I also have a Proceed Amp 5 that has crapped out as well, but that is for another time. So let loose with any questions or criticisms, as I would like to see if I can power up this heavy amp.

This last picture is of the bad component showing what looks to be some discoloration due to excessive heat (As in it let the smoke out)



__________________

[jacketfan]

Not sure if I did not frame a question properly, but would like to know if anyone has a recommendation of where to go with trouble shooting and repairing this card.

[c2cthomas]

I couldn't find any schematics or service manuals for your amp - although you might be able to request a reprint from the Mark Levinson site if you explain your situation - MarkLevinson - Home

What I suggest when I have a known good example to compare to is to:
1) Sit the two PWB's next to each other and break out a BIG notepad.
2) Make point to point resistance measurements and compare the good board with the bad board.
3) Voltage checks will help - but you will need to get the bad board to give up that nasty smoking habit first - and for some - it's hard for 'em to quit!
Note - without a schematic taking a digital photo of the board and doing a printout that you can label the test points on can work pretty good. Not as well as a circuit diagram - but it might be enough to get you there.

Hope that you find this of at least some help........

[nac134]

Without a schematic, you will only be able to fix the problem if it is rather simple. You have a couple of suspect parts, and you need to test them. It is very important that you remove them from the board before doing this.
Removing parts from a surface mount board is very easy, but you need to know how before you try, or you could muck it up. There are many good videos on youtube that will show you how - search for "desoldering". You probably want to use desoldering braid, rather than a desoldering pump. Check out a few videos, and you will see how little skill is needed. Test the parts once you have them out. Once you do that, post your results on this thread, and Ill help you plot your next move.

[singa]

Hi jacketfan,
Replacing the resistors may not help if you don't check the
output transistors for short or open and other parts.Time to learn to use a multimeter.

There is one important observation and that is the black resistor being
used to replace the 5W white ceramic resistor.From the size ,it is too small
even if it is the same value.I'm surprised it did not burn out but maybe the
technician readjusted to a lower bias.A dirty trick no less.

Some of the resistors are 1% tolerance,so you may have difficulty
finding them in big wattage of 1 to 2 watt but in all case you can substitute 5% types but of course the circuit will drift a bit. Best of luck.

Discharge the power caps before you go in with a suitable 5-10W resistor
of 1 K ohm or more to ground and measure the residual voltage left at the
caps to check if they are fully discharged. singa.

[godfrey]

Hi
If you're lucky, the same components have failed as last time. That would make it a lot simpler. The black and white components do look like resistors. Have you measured them and compared to the same components on another good board?

Don't compare to the previously repaired one though, since that got patched up with wrong-valued parts anyway. You can test with a multimeter set to "resistance". It's best to measure each component both ways around as you might get different answers depending what else they're connected to.

Originally Posted by jacketfan

As I look around this forum, I can tell I am out of my league...

That's a good enough reason to be here. Welcome to the forum.

[godfrey]

Originally Posted by singa

There is one important observation and that is the black resistor being used to replace the 5W white ceramic resistor.From the size ,it is too small even if it is the same value.I'm surprised it did not burn out but maybe the technician readjusted to a lower bias.A dirty trick no less.

Agreed about the under-sized replacement. Oddly enough it's quite a high value though (1.8K), so obviously not for bias stabilization. Maybe part of the feedback network, which would make such a lousy repair doubly diabolical.

On the up-side, the OP's probably already better qualified to work on the amp than the last guy who fixed it. (Hey, at least he bothered to look at the writing on the components)

[jacketfan]

Gentlemen,

I greatly appreciate your assistance. c2thomas, I appreciate your reference to a smoking habit. I have let the smoke out of way to many things electrical.

I have a email in to Harman, and I also searched for circuit diagrams. I suspect, Harman may be reluctant to provide such information.

My background is in Aerospace Engineering, so I have some familiarity with electronics, but by no means consider myself anything but a newbie at this. The best I have done is speaker crossovers and a LT circuit for a subwoofer.

I have ordered replacement resistors and will give that a shot by replacing the two resistors that were bad on the "bad" board.

I have a cheap multimeter, so if there is anything else I need, let me know and I will add to the tool collection.

As far as desolering, I am not sure I have the skills to remove the board from the heat sink. So my plan right now is to do the same sort of cheezy fix the bozo that did the previous fix did.

I will update if I get anything from Harman and when I get the resistors redone.

This amp has been powering Maggie 3.6s for quite a few years now, and I would like to continue.

Thanks again for your assistance,

Mark

[godfrey]

Originally Posted by jacketfan

So my plan right now is to do the same sort of cheezy fix the bozo that did the previous fix did.

How about clipping off the old components, then soldering the new ones to what's left of the old component's leads? It's not perfect, but better than the previous job - at least you're getting the "dead" stuff out of the circuit. Remember, it may only be half-dead.

[c2cthomas]

Hi Mark - when I said take a photo and insert some test points on it I intended something like the attached photo.

Mark it up (no pun intended) and then on the note pad record your findings.

Next up on test equipment to acquire would be a o'scope and audio signal generator IF you really want to get into the building electronics side of this hobby. Not really worth the price of admission unless you plan to get some usage outta 'em tho.