CurtPalme.com Home Theater Forum

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Heywood Jablome · Joined: 12 Mar 2006 Posts: 1548

I'm going to take the amp to work and perform the tests in the service manual that require a signal generator.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

For those of you following along in hopes of learning, you can see how this can sometimes be frustrating. What they are going to attempt now is to follow trouble shooting as described in the manual which requires certain equipment.

But I'll give you others another option that to me is simpler. First you need the schematics and know how to basically read them. Like Chip already did you need to verify voltages and relay closing. Now Chip did ohm out the speaker and it seemed good but if it was me I would be testing that speaker on another stereo just to hear it make sound.

Next you need an old stereo with a preamp input, like aux or cd. And an old spearker hooked up to one side of the stereo, say right side. Now take an old RCA ended cable, like the ones to hook up the cd to the stereo. Cut one end off and strip it back to reveal the 2 wires. Connect the ground wire to the amp gnd and the positive end to the end of you DMM test leed the plugs into the meter. The other end is now a probe. Hook the cable up to your test stereo.Turn on your test stereo, turn on your device hooked up to the sub which is probably another receiver, turn on the amp. Now locate on the schematic where your signal first comes into the sub. Touch your probe on the board at that location and you should have sound come out of your test speaker. If you do then locate your preamp signal on the schematic to where it enters the output section. Touch your probe there and see if you have sound. If you do then your problem is in the output section. If you dont then work your way back through the signal chain by looking at the schematic.

This method could also be used to check the output section by connecting your probe test meter end to a preamp output of a receiver and the other end of the probe to the input of the output section and sound should come out of the sub speaker.

I think I explained it fairly simple, I know its simple in my head... Shocked

Hmmm, does that mean I'm simple minded.. Laughing

Heywood Jablome · Joined: 12 Mar 2006 Posts: 1548

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

stefuel · Posted: Mon Apr 06, 2009 9:07 pm Post subject:

I was curious what you had in mind with another amp and speaker. Using the amp to probe for signal is a great idea.
Kind of like following the yellow brick road Thumbs Up

Heywood Jablome · Joined: 12 Mar 2006 Posts: 1548

**AnalogRocks** · Posted: Mon Apr 06, 2009 10:54 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

stefuel · Posted: Wed Apr 08, 2009 10:20 am Post subject:

It will be interesting to see the results of the amps visit to Heywoods lab at work. There's probably one .35 cent part that I missed. The other thing is as I mentioned earlier, someone other than me had been putzing around inside the amp as at least two parts had been hacked in and were incorrect. Probably what I should have done first is to look at the re-soldering on the trace side and compaired all those parts to the stock list.

Heywood Jablome · Joined: 12 Mar 2006 Posts: 1548

I don't have any faith i my first pass with a function generator, OR my too-fast readthru of the service manual.
I'm going to give it a more full run-thru after hours I think.

stefuel · Posted: Fri Apr 10, 2009 10:33 am Post subject:

When you look at it, you'll notice more re soldering then I did. The only soldering I did was to replace all three IC's, the two zener diodes, the ribbon cable on both ends and of course the two burned resistors. The two diodes are the correct voltage but higher capacity.

stefuel · Posted: Sun Apr 12, 2009 11:38 am Post subject:

Heywood's got the amp right now so I can't do anything else with it for the time being but something is bothering me about this. I keep looking at the schematic and don't see anything that would/should generate the "breathing" that it does at power-up. I'm starting to think the reference to "breathing" in the manual means something else and what I'm seeing is part of the actual problem.
I'm starting to think the reference to "breathing" is the manuals author's way of saying it's alive.

**Curt Palme** · Posted: Sun Apr 12, 2009 1:56 pm Post subject:

That's why you read reviews that the sound is airy.. Very Happy

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I'm curious Chip. When you were testing the sub, were you using the preamp input and were you connected to both inputs (left and right) ?

stefuel · Posted: Sun Apr 12, 2009 9:44 pm Post subject:

stefuel · Posted: Wed Apr 15, 2009 12:56 am Post subject:

Well the amp's on the way back. Not sufficient time at Heywoods work to spend much time on it so it looks like I'm going to have to gyver it Wink

I'll have the extra amp, speaker and probes ready to go.

Side note: Heywood did say that he found 15vdc at a test point where only 300mv should be but I'm not sure where at this time.

stefuel · Posted: Thu Apr 16, 2009 9:47 pm Post subject:

OK I have the amp back and it's time to "Alien Anal probe" it. I'm sitting here looking at it, thinking a good place to start would be the ribbon connector between the two boards. It's a five wire ribbon. I'll have to check the schematic and try to figure out which wire the signal would be on to feed the amp section. That shouldn't be hard. If I can't get a signal at the ribbon connector then it's in the pre-amp section. If I do have signal then the problem is in the amp section. I must now construct the alien anal probe Laughing

stefuel · Posted: Thu Apr 16, 2009 11:59 pm Post subject:

Mac will be proud of me. My new alien anal probe looks like it came straight from the mother ship, industrial strength and fused to boot. Laughing

I told you that there were some here that were really out there and I'm one of them Mr. Green

Now it's time to study the schematic and make a list of test points.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508