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Old 12th February 2008, 04:40 PM   #1
cwahls is offline cwahls  United States
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Default Samson Servo 550 issues, multiple amps, same issue.

Good morning! Wonderful forum!

We have 8 Samson Servo 550s and 3 of them are having the same issue. Won't come out of protect, no DC on the speaker outputs (before the relays), thermistor is good, yaddada yaddada.

There was obvious discoloration on the PCB and resistors themselves that buffer the TA7317P protection IC I replaced these even though they tested in spec OUT of operating conditions.

What are the chances I have a bad TA7317P? In searching I read that they are the most common IC unnecessarily replaced

The amplifiers ARE in an area that runs warm, that is getting changed, they are not run hard and 95% of their life they spend idling or barely working (Classroom use.) Is this chip prone to failure in high temperatures? I've just not dealt with this protection scheme before and hoping someone who has can give me a nudge in the right direction.

Any ideas? Unfortunately I don't have any spares of these IC's to just shotgun in there. Is this a common issue. Samson tech support was of ABSOLUTELY no help. I figured if I have 3 of 8 doing this then certainly they may have seen it before

I can post a schematic if someone wants one.


Many thanks! Chad
Chad
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Old 13th February 2008, 04:11 PM   #2
cwahls is offline cwahls  United States
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Bump I guess
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Old 13th February 2008, 04:22 PM   #3
burbeck is offline burbeck  United Kingdom
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hi Chad,
odds on its a dryed up electrolytic cap around this chip
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Old 14th February 2008, 07:55 PM   #4
cwahls is offline cwahls  United States
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Thanks, I'll certainly check that!

Chad
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Old 14th February 2008, 10:54 PM   #5
cwahls is offline cwahls  United States
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Quote:
Originally posted by burbeck
hi Chad,
odds on its a dryed up electrolytic cap around this chip

I owe you a beer, it's up and running, what a finiky bugger in a high heat area, upgraded to hi temp caps

You Da Man! So it IS indeed the most unnecessarily replaced IC
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Old 15th February 2008, 10:18 AM   #6
burbeck is offline burbeck  United Kingdom
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hi Chad,
glad you got it sorted
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Old 9th April 2012, 06:50 AM   #7
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cwahls- I just had the same issue with my servo 550 and the caps were clearly dried up so I replaced them and still have the issue. Did you have to replace anything else in the unit to get it working again???
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Old 9th April 2012, 05:37 PM   #8
cwahls is offline cwahls  United States
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Nope, just the caps IIRC, I MAY have replaced a resistor that got a little warm, it's been a while. That's a HOT area in the amplifier. I used a quality hi-temp cap and all 4 of them have been going strong for 4 years now. I just shotgunned all of them instead of repairing them as they fail, usually when it's most inconvenient.
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Old 9th April 2012, 05:50 PM   #9
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Thanks for the reply. I guess I'll have to start poking around at transistors and whatnot. I tested all of the nearby resistors because I noticed it was a high heat area but they all tested to spec. If anyone else has any ideas of where I should point my investigation it would be appreciated!
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Old 9th April 2012, 06:29 PM   #10
cwahls is offline cwahls  United States
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see if there's a reason it's in fault, as in check to see if there is DC on the output before the speaker relay, and check for appropriate rail voltage on both LV and HV also filtering on the HV rails.

How do the rail caps look, those are heat persnickity too. are they bulged up at all (press down on the plastic top and feel for metal bulging)
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