DAC 2496 (AK4393) DAC KIT With CS8416+AK4393+5532 - Page 139 - diyAudio
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Old 21st March 2012, 11:05 PM   #1381
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Originally Posted by 50AE View Post
Thanks again for your fast and kind answer.
You're welcome
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Old 22nd March 2012, 10:58 AM   #1382
bcmbob is offline bcmbob  United States
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Shucks ! No luck

After completing the kit I got active "Power" indication and nothing else. Using the same source and coax that works perfectly with the Lexicon unit - no other LEDs would light. No sound but there was a slight hiss and some low 60 cycle shadow noise.

Things I checked:
1. 17.8 and 11.1 VAC to power terminals. (though rated 15/9 on label)
2. No temp beyond room temperatures on board or toroid.
3. No visible solder bridges.
4. 1.6 VDC across both audio out RCAs

Luckily, no other equipment was damaged, but turning up the volume pot on the MyRef Integrated amp caused both LM3886 to trigger their protection circuits. Going back to PC --> Lexicon --> Integrated Amp was fully functional again.

The only other possible mistake was initially not using the Euro-style terminal on the 15-0-15 power in. I made direct connections to the board. I don't know if that could cause a problem.

Please review the pics for anything I'm not seeing
Attached Images
File Type: jpg Mini 01.jpg (78.4 KB, 499 views)
File Type: jpg mini 1.jpg (558.6 KB, 493 views)
File Type: jpg Mini 2.jpg (652.2 KB, 464 views)
File Type: jpg Mini 3.jpg (622.2 KB, 440 views)
File Type: jpg Mini 4.jpg (693.6 KB, 419 views)
File Type: jpg mini bot.jpg (205.3 KB, 144 views)
File Type: jpg mini read.jpg (257.7 KB, 156 views)
File Type: jpg T vr.jpg (43.2 KB, 166 views)
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Last edited by bcmbob; 22nd March 2012 at 11:01 AM.
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Old 22nd March 2012, 11:39 AM   #1383
F1 FAN is offline F1 FAN  Canada
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Do you have the +and -12 volts at the opamp power pins?
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Old 22nd March 2012, 11:45 AM   #1384
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Quote:
Originally Posted by bcmbob View Post
After completing the kit I got active "Power" indication and nothing else. Using the same source and coax that works perfectly with the Lexicon unit - no other LEDs would light. No sound but there was a slight hiss and some low 60 cycle shadow noise.

Things I checked:
1. 17.8 and 11.1 VAC to power terminals. (though rated 15/9 on label)
2. No temp beyond room temperatures on board or toroid.
3. No visible solder bridges.
4. 1.6 VDC across both audio out RCAs
Hi Bob,

I can't see obvious errors but the DC offset make me think of opamp's rails.

I would measure:
  • analog AC rails vs ground
  • DC entering the regulators
  • DC leaving the regulators
  • opamp rails
When no input is present (SPDIF) a slight hiss is normal.
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File Type: jpg mini2496.jpg (362.8 KB, 812 views)
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Old 22nd March 2012, 02:55 PM   #1385
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Hi Dario,

I've got some MC7912CT (Motorola) and UA7812C (T.I.)... I noticed that you spec'd On Semiconductor... Is there a big difference IYO?

Thanks
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Old 22nd March 2012, 04:00 PM   #1386
bcmbob is offline bcmbob  United States
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A couple questions before I start poking around.

1. Which group is referred too as "digital" - which analog (123 vs ABC)?
2. What's the best spot to pick for ground to do the opamp readings?
3. Please confirm rails are picked up direcrly from legs of 15V chips - 1,2 & 3. ( just noticed one is L7912CV the other is L7612CV)

Please bear with my lack of confidence/knowledge in this area. Gives me the he-be-gee-bees Remember - I'm an ears guy not a schematic scholar.
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File Type: jpg Mini cut.jpg (459.6 KB, 242 views)
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Last edited by bcmbob; 22nd March 2012 at 04:06 PM.
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Old 22nd March 2012, 04:10 PM   #1387
bcmbob is offline bcmbob  United States
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Giovanni - Your answer was the exact information I was looking for. Thanks!
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Last edited by bcmbob; 22nd March 2012 at 04:12 PM.
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Old 22nd March 2012, 06:44 PM   #1388
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Quote:
Originally Posted by DarpMalone View Post
I've got some MC7912CT (Motorola) and UA7812C (T.I.)... I noticed that you spec'd On Semiconductor... Is there a big difference IYO?
Yes, there's a big difference, IMHO, otherwise why bother changing them...

Motorola are exactly the same part (On Semiconductors is the old Motorola Semiconductors Division...) so the MC7912CT are OK.

TI parts are like the others so you should order some On Semi MC7812

Quote:
Originally Posted by bcmbob View Post
1. Which group is referred too as "digital" - which analog (123 vs ABC)?
The analog section is the one where I put values in the picture I've attahced in my previous post (7812, 7912, LM1117-5)

Quote:
Originally Posted by bcmbob View Post
2. What's the best spot to pick for ground to do the opamp readings?
The nearest will do (see where I've indicated 0V)

Quote:
Originally Posted by bcmbob View Post
3. Please confirm rails are picked up direcrly from legs of 15V chips - 1,2 & 3. ( just noticed one is L7912CV the other is L7612CV)
No, only 2 and 3 are the 15V analog regs one posistive (7812) one negative (7912).

Pay attention! 7812 and 7912 have different pinout!! See my picture for reference.

Dario
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Old 22nd March 2012, 08:13 PM   #1389
bcmbob is offline bcmbob  United States
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This is what I get. Red dot = gnd/neg probe placement - except for green arrow for opamp readings. Right side chip sure looks like L7612CV to me. Would that be wrong part?
Attached Images
File Type: jpg Mini cut 2.jpg (592.3 KB, 189 views)
File Type: jpg Regx2.jpg (75.1 KB, 166 views)
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Old 22nd March 2012, 08:23 PM   #1390
F1 FAN is offline F1 FAN  Canada
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Quote:
Originally Posted by bcmbob View Post
This is what I get. Red dot = gnd/neg probe placement - except for green arrow for opamp readings. Right side chip sure looks like L7612CV to me. Would that be wrong part?
I'd say it's a 7812(bad stamp on the 8) but you have the 79 and 78 in the wrong positions.
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