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Old 25th March 2008, 10:09 PM   #1
shagone is offline shagone  United States
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Join Date: Apr 2007
Question Xtant X1001

I am working on an Xtant X1001 with very weak intermittent output.

there is a red led near the gain pot on the upper left corner of the amp. this led is not labeled on power up it lights up and i get distorted weak audio for a second or two and then the led goes out along with the audio. what is this red led for?

the amp has 8 slightly bulging big caps that filter the power supply ripple. there appeares to be a ring around 2 of the caps as if it leaked and dried to the board but it could be someting else because this amp was on a boat?? i pulled one of the suspect caps and it was just slightly out of tolerance if at all. i ordered all 8 just in case.

there were 2 bad resistors in the power supply drive circuit and it looks like another tech changed the 4 smt driver transistors. all 4 are the same part, is this correct?

at first the amp buzzed and had the low impedance light on but after changing the 2 smt resistors in the drive circuit and touching up some dry solder joints and cleaning up the board that went away. now the current is normal but the amp cuts out as stated above.

there are 2 332k smt resistors below the p/s drive transitors that check to be out of tolerance. i'm working on getting these in but i'm looking for any ideas from anyone who may have worked on one of these before.
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Old 25th March 2008, 10:54 PM   #2
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Location: Louisiana
LED236 lights when the amp comes out of mute/protection. If it's going off, the amp is going into protection for some reason (low/high input voltage, overcurrent, thermal...)

If there is excessive ripple on the caps/rail voltage, you need to replace them before you can troubleshoot the rest of the problems.

The electrolyte is conductive and corrosive. If the caps have leaked and the electrolyte has eaten into traces passing under the caps, it can cause problems.

Were the tops of the caps actually bulging or is it only the plastic cover that's bulging? If you can push it down and it pops up again, it's only the plastic.

All 4 transistors are PZTA56. The two 10 ohm resistors commonly open.

Did you desolder the resistors to check them? They are for regulation of the power supply rail voltage. There's very little chance that they have failed (but I've seen stranger things happen).
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Old 25th March 2008, 11:20 PM   #3
shagone is offline shagone  United States
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the red led goes out but none of the low/high input voltage, overcurrent, thermal... led's come on. is this normal?

i pulled the plastic cover off 2 of the caps that were bulging and the cap itself was slightly bulging on the top. the corrosion is very light on the board but ill pull all the caps and clean it better. the electrolyte ran under a small bipolar box cap that is up top near the sync mounted fets. i'll try to pull that too and check/ clean it and replace it if need be.

all 4 a56's seem like thay were changed but check ok. the last guy missed the 10 ohm resistors but i replaced them. is there supposed to be a 1k resistor between the two 10 ohms? what does it do?

i have not yet pulled the 332k resistors to check them but they both read different numbers in circuit and are way off from 332k. i'll pull them and re-check. they look slightly corroded too.

the small drive transformer next to the 4 a56's was resoldered by the last tech too. what could be the reason or issues with this? i don't read any shorts between the primary and secondary. what voltage should i read here?

the owner of this amp said that he took it to la jolla audio and the tech there said that he helped design this amp or something i think i'll throw out the B.S. flag on that one because he didn't fix it or at least not right the first time.

i forgot to metion that all of the sync mounted components pass initial tests for shorts and appear to all be original judging by the solder joints.
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Old 26th March 2008, 01:25 AM   #4
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Location: Louisiana
Can you post the DC voltage on the LM311 and the LM339 before and after the LED236 goes off?

For the LM339, use chassis ground as the reference (black meter lead).

When measuring the voltage on the lm311, you must be VERY careful. The IC is connected to the negative rail. Don't let your probes slip and don't accidentally touch the metal part of the probe. For the LM311, use pin 4 of the IC as the reference.

The 1k resistor appears to be a snubber/damper.



LM311 - LED236 on
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

LM311 - LED236 off
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:


LM339 - LED236 on
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:


LM339 - LED236 off
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
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Old 31st March 2008, 08:33 PM   #5
shagone is offline shagone  United States
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sorry i took so long to reply, i was waiting on the 8 replacement big caps to come in. it turns out that the originals were all reding within tolerance but they didn't look to be in good shape and there was a strange substance under the last 3 of them on the board. it could have been the cap leaking slightly.

after cleaning up the board and replacing all suspect caps including the small box cap and touching up solder connections including the solder points on those 332k resistors (they were fine out of circuit?) the amp worked fine.

this amp draws close to 4 amps at idle and has a 25 amp spike at power up to charge the big caps i guess.

i know this is a very powerfull amp but is this normal?

Thanks again Perry for your knowledge!!
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Old 31st March 2008, 11:48 PM   #6
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Location: Louisiana
The turn on spike is normal.

The 4 amps of current draw is probably not normal. I have one here and checked the current draw. It's ~1.3 amps at idle after the caps charge.

I won't have this amp much longer. If you need any information from it, you need to ask before the end of the week.
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Old 1st April 2008, 08:14 PM   #7
shagone is offline shagone  United States
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at what voltage did you read 1.3 amps? i'm running at 13.8 volts. i will read the exact amps to verify. i was guessing 4 amps by looking at the ammeter on my supply it may be closer to 3. if i remember correctly it goes down as i turn the voltage down.

the amp seems to run fine. the only thing that really runs hot are the two big inductors on the upper left side of the amp that i believe are for the audio output filtering. i think these usualy run hot but correct me if i'm wrong.
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Old 1st April 2008, 10:18 PM   #8
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Location: Louisiana
I didn't measure the input voltage but my supply is generally set to ~13.5v.

The current draw shouldn't change with minor voltage variations.

What is the rail voltage on your amp?

How fast do they get hot?

How hot do they get at idle after 10 minutes (no speaker load)?

Was this (4a draw) with or without a speaker/dummy load connected to the amp?
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Old 9th April 2008, 07:03 PM   #9
shagone is offline shagone  United States
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At idle with no load connected with 13.5 volts i was reading just under 3 amps with my fluke meter.

i forgot to double check the rail voltage but it was around 100 volts??

the coils only got hot after a few minutes with a load connected and music playing. without the load they were only barely warm after 10 minutes.

i ran the amp hard for another hour with no problems. i think it's ok and just a current hog (i hope).
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Old 9th April 2008, 09:57 PM   #10
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I think the amp is probably OK.
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