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Pimeta Troubleshooting

post #1 of 16
Thread Starter 
Using two 9v alkaline batteries in series for testing. Getting 18.5v. Single BUF634s at all positions. AD8610/8620 for OPAG/OPALR. IG to 8610 pin 7 (V+) = 8v. IG to 8620 pin 8 (V+) = 9.24v. Current sources installed. IG to 8620 pin 1 (OUTA) = 8.93v. IG to 8620 pin 7 (OUTB) = 8.68v. IG to 8620 pins 2, 3, 5 & 6 = 7.6v (should be 0, shouldn't it?). IG to 8620 pin 4 = -9.16v. With BUF643s installed, IG to BUFL & BUFR pins 6 = 8.0v. IG to BUFG pin 6 = 7.72v. IG to OL = 7.95v. IG to OR = 7.92v. IG to OG = 7.68v. IG to BUFG pin 7 (V+) = 8.95v. IG to BUFG pin 4 (V-) = -8.94v. 8610 pin 4 (V-) to pin 7 (V+) = 18.6v. 8620 pin 4 (V-) to pin 8 (V+) = 18.03v. OG to OR = 259mV. OG to OL = 266.5mV. Board was cleaned when each component was installed and I have used a magnifying glass, and continuity check on DMM, to validate solder joints. Nothing seems to get warm. Any ideas? 8620 done?
post #2 of 16
Well, what is the actualy problem with the amp?
post #3 of 16
I'm going to guess from the values in the previous post, DC offset?

Any way we can get some pictures?
post #4 of 16
Quote:
... OG to OR = 259mV. OG to OL = 266.5mV.
Yeah, that's the key right there - over 250mV of offset on both channels.

As Pddjsteve says, photos, please?
post #5 of 16
Thread Starter 
Sorry, I just don't have a digital camera with enough resolution to produce a close-up of something this small. It ends up being way too fuzzy. Guess I ought to move into the 21 century and buy one, but photography hasn't been one of my hobbies since way back in the 35mm film days. Maybe I'll take a look to see what BestBuy has this afternoon.
post #6 of 16
The first thing I would probably do is to remove the class A biasing
Quote:
Current sources installed.
Your IG-> OG is a big problem, and indicates that your ground channel isn't working (possible bad 8610).
post #7 of 16
Personally I would remove the opamps and the buffers (hopefully socketed) and check the voltage at all of the individual pads and report the results. you should be able to search and find threads with similar readings taken on working PIMETAs.

Bottom line - any number of things could be causing the offset issue and we currently don't have enough info to help.
post #8 of 16
Thread Starter 

Pictures

Pictures are attached. Actually they were a great tool. I was able to magnify the source 3.5MB photos to a great extent so that I could verify the status of the solder joints. Don't know how much they will show after resizing downward to an attachable size. Unfortunately, as you'll see, I did not socket the opamps as I was not interested in rolling different flavors (it will be the girlfriend's amp). I have a couple more inbound that I will socket, so I'll just clip these and take readings when I can get some time.
post #9 of 16
Those pictures are tiny. You can upload higher resolution ones to someplace like imageshack.us and link to them.

Looks like you are using an 8pin TLE2426. Which pins do you have connected?
post #10 of 16
Thread Starter 
I'll see if I can get the pics hosted today. The company IS nazis block Head-Fi from internet access, so I'll try to re-post the host link tonight. I don't know what the automated blocker finds objectionable in the site header. I used pins 1, 2 & 3 on the 8-pin version of the TLE2426. So, in order from closest to the capacitor bank, the pins are "In", "Common" and "Out".
post #11 of 16
Thread Starter 
post #12 of 16
Looks like the AD8610 is mounted backwards. Most likely it is toasted.
post #13 of 16
Uh yeah, that's a ditto on the AD8610 being backwards.
post #14 of 16
Thread Starter 
OK, removed AD8610, AD8620, BUFG, BUFL & BUFR. Using two 9 volt alkaline batteries in series, I got the following voltage readings relative to OG:

OPAG
pin voltage
1 260mV climbing
2 120mV climbing
3 0
4 -9.22v
5 -4.4mV
6 -60mV falling
7 9.22v
8 45mV

OPAL/R
pin voltage
1 -9.19v
2 -39.6mV
3 0
4 -9.2v
5 0
6 -39.7mV
7 -9.19v
8 9.22v

BUFG
pin voltage
1 -9.2v
2 265mV falling
3 250mV climbing
4 -9.2v
5 200mV climbing
6 -2.8mV falling
7 9.2v
8 9.2v

BUFL
pin voltage
1 -9.21v
2 90mV climbing
3 -9.2v
4 -9.2v
5 123mV falling
6 -9.1mV
7 9.22v
8 9.22v

BUFR
pin voltage
1 -9.2v
2 96mV climbing
3 -9.19v
4 -9.16v
5 -9.2v
6 -9.2v
7 9.21v
8 9.21v

Seems to be an inconsistency on pin 5 between BUFL and BUFR. Does this data offer any additional clues?
post #15 of 16
Pin 5 is not connected to anything. According to the datasheet it does nothing. On the circuit board it is just a solder pad connected to nothing (except to the corresponding pin 8 on the SOIC pad).

Pin 8 is also listed as NC in the datasheet, but on the board it is tied to V+ so should have the same voltage as pin 7.

Since you are getting some kind of voltage on those pins I would check for stray solder, or clean off the flux, some types are conductive.

Pin 2 is also listed as NC. That 90mv may just be some parasitic voltage it is picking up from traces nearby. Or it could be the flux.
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