CurtPalme.com Home Theater Forum

stefuel · Posted: Fri Apr 17, 2009 2:25 am Post subject:

stefuel · Posted: Fri Apr 17, 2009 10:43 am Post subject:

OK I fell asleep last night studying the schematic for test points for the alien anal probe. Best I can figure, all inputs combine at pin 6 (input) IC 1 and outputs on pin 7. then the next logical test point looks like pin 6 (input) on IC 2 and outputs on pin 7 which is after VR 1 but before VR 2 which is the level pot. From there it's off to the amp section via ribbon cable lead #1 of 5.
VR 2 looks to have been replaced or at least re-soldered. If I have signal at lead 1 of the ribbon connector, I should be able to test the operation of VR 2 by listening for sound at lead 1 and adjusting VR 2 ???

I'm pretty sure this is all I need to confirm PCB 2

stefuel · Posted: Fri Apr 17, 2009 4:30 pm Post subject:

Som-bitch, the alien anal probe has put me on the right track. I tried ribbon connection #1 and had no signal so I back-tracked until I did. I have signal to pin 6 on IC 1 (input) but not pin 7 (output) Why, brand new IC. I then re-checked votltage at pins 4 and 11. AhaaaaaaPin 4 should have +16 and pin 11 should have -16. Both have -16. Back to the schematic and trouble shooting flow-chart "with troubles on the 16V rail, check and replace as needed C5, C6, C7 and C8." My money is on C7 as that is next in line and right next to R2 which was one of the fried resistors. It looked physically fine so I left it alone.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I'm paying attention, just awaiting your findings.......... Smile

if you get lost just let me know.

stefuel · Posted: Fri Apr 17, 2009 7:47 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

OK. One thing I want you to check real quick, just to eliminate it as the problem is R54, 10ohm. It should be on PCB-1. Let me know.

stefuel · Posted: Fri Apr 17, 2009 8:20 pm Post subject:

stefuel · Posted: Fri Apr 17, 2009 8:32 pm Post subject:

Time to mount it in the cabinet for the real test.

stefuel · Posted: Sat Apr 18, 2009 3:22 am Post subject:

Well I solved one problem but it's not finished yet. The issue with getting the signal to the amp is solved. The input/filter board now has signal on ribbon wire 1 to the main amp. Using the alien anal probe shows there is a clean signal to the amp. the filter is working as there is nothing but low clean bass at wire 1. However, when I installed the amp in the cabinet, hooked up to the speaker and to a input, I flip the power switch and the second the relay closes, I get what sounds like the nastiest feedback you ever heard. It does it with or without connection and with the level turned all the way down. There is one other place that I might have lost a hairline trace but I have to work tomorrow and don't want to get involved with something I can't finish. So I'll get back to it on Sunday.

**Curt Palme** · Posted: Sat Apr 18, 2009 3:28 am Post subject:

89 posts for a lowly 10" woofer? I wonder what would happen if I posted about a double 18"? Smile

Chip, send the manual to curtpalme@shaw.ca. 10 meg limit there though.

Put up some pic of the amp module. I wanna see what kind of parts the output section uses.

stefuel · Posted: Sat Apr 18, 2009 4:05 am Post subject:

stefuel · Posted: Sat Apr 18, 2009 2:00 pm Post subject:

"89 posts for a lowly 10" woofer? I wonder what would happen if I posted about a double 18"?"

178 posts

Heywood Jablome · Joined: 12 Mar 2006 Posts: 1548

Chip's rockstar name is "Tenacious C" Mr. Green

**Curt Palme** · Posted: Sun Apr 19, 2009 11:22 pm Post subject:

OK, I'll jump in now, Chip, forget the second email, you answered above.

If you can send me an audio clip of the noise, that would be good. I wanna know if it's motorboating, 120Hz hum, an open feedback loop somewhere or ??

Since the relay clicks closed, and you get a loud sound, we can assume that most of the amp section is OK. SInce however the volume control at 0 still produces the sound, then either the problem is in the amp section or the power supply driving the amp section.

You need to scope the main power supply. If you have no scope, you can meter it as well. If one side of the balanced power supply is say 2-3 volts lower than the other, you can assume that one of the big filter caps is open. A true balanced supply should be within about 1 volt of each other.

Another possibility is that an op amp has a missing feedback resistor, or it or the trace (most likely) is open. That causes exceptionally high gain of that op amp, and iit will oscillate.

For example, R19 and R25 are feedback resistors in the input stage, but I also see others in the power amp section as well. Measure those resistors across the pins of the IC, to make sure both sides of the resistor are making connections to the chip. Minor problem is, the chip and other parts might throw off the value of the resistor a bit. As long as you read the rated value of the resistor or lower, you should be fine.

Also, take the negative side of C24 and short it to ground. That will short out all signals coming from the input stage from getting to the power amplifier section, which starts at the base of Q 4.

Last thing: Take an old amp or receiver, couple the input 'hot' lead with a 10Uf, 100 volt capacitor to a test probe, connect the negative side to the amp chassis, and you've got a signal tracer, that allows you to feed signals of the woofer to another amplifier and speaker that you know works. You can then connect the capacitor to each output of each op amp to see where the noise starts from.

You're close... Smile

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Oh sure. Hop in now at the easy part. Smile

This was suppose to be a learning session for Chip..... Wink

Now your fixing it for him..... Smile

**Curt Palme** · Posted: Mon Apr 20, 2009 12:51 am Post subject:

I can hit delete.. Smile

I think most of my points are steering him in the right direction as to what part of the amp to look in depending on the sound the amp is making.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I was going to say you can have sloppy seconds...but.....wait......I just said it....... Laughing

**Curt Palme** · Posted: Mon Apr 20, 2009 1:42 am Post subject:

A well built woofer can take all you gots, and come back for seconds. Very Happy

stefuel · Posted: Mon Apr 20, 2009 12:35 pm Post subject:

The input to R2 and R3 which is just after the 10,000uf filter caps is less than 1/4 volt difference. I was going to test those caps but my meter is limited to 4,000uf. I'll check the other things mentioned after lunch. I have to clean the house for company later,