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
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
burbeck said:
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
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???
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.
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!
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)
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)
I measure 35 millivolts dc at the incoming pin of the TA7317P protection chip. Do you know what the chip considers too much dc voltage? or is it just if there is any dc incoming at all?
all my caps look fine. I need to get a cap tester to actually test them...
all my caps look fine. I need to get a cap tester to actually test them...
don't know what it wants to see, I MAY have prints for it in electronic form.
Have a scope? look a the outputs, both of them, just before the speaker protection relay. That will tell you a lot.
Have a scope? look a the outputs, both of them, just before the speaker protection relay. That will tell you a lot.
All my voltages coming from the transformer are correct but in my poking around I noticed a pair of burnt resistors that I somehow missed before. They measured at about four times the impedance they should so I am working on getting them. unfortunately there are no electrical component suppliers in my city for some reason. I'll replace those and see where I'm at.
unfortunately I do not have a scope.
Also I did find the datasheet and the protection IC looks for +/-1.1 V so that is in spec for that. The resistors appear in the schematic like they may be preventing the correct voltage to the relays so hopefully replacing those helps.
unfortunately I do not have a scope.
Also I did find the datasheet and the protection IC looks for +/-1.1 V so that is in spec for that. The resistors appear in the schematic like they may be preventing the correct voltage to the relays so hopefully replacing those helps.
OK, Amplifier output goes into relays, is there DC there? On the guzinta of the relays. Not the comezata, they are not energized in protect.
Did you look at the HV and LV rails? With a Meter, set for DC, using the negative speaker lead as a ground reference. A chassis screwhole probably will work too.
You can use the finals to check HV rail voltage and pin 4 and 8 on an op-amp to check LV
Did you look at the HV and LV rails? With a Meter, set for DC, using the negative speaker lead as a ground reference. A chassis screwhole probably will work too.
You can use the finals to check HV rail voltage and pin 4 and 8 on an op-amp to check LV
on one channel at the guzinta of the relay i have 6.0 millivolts and the other i have 0.7 millivolts
on the HV rail i have between 74 and 75 volts
LV has between 14 and 15 volts
Am i supposed to get shocked when i touch a heat sink that a transistor is bolted to? never had that happen before...
on the HV rail i have between 74 and 75 volts
LV has between 14 and 15 volts
Am i supposed to get shocked when i touch a heat sink that a transistor is bolted to? never had that happen before...
Okay now that I feel like a rookie and have that cleared up after a little reasearch...
I tested the four transistors that had their own individual heat sinks and they are good. (though i thought it strange that two of them had +75V on the heat sink and two of them had -75V on their heat sinks, probably just me being a rookie..)
Is my next step testing the output transistors?
I tested the four transistors that had their own individual heat sinks and they are good. (though i thought it strange that two of them had +75V on the heat sink and two of them had -75V on their heat sinks, probably just me being a rookie..)
Is my next step testing the output transistors?
Don't know if you have the schematic but here is a link to one: Samson 550/260/170 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
I read your other thread on the 200 and the relay is one of the big issues on these models (200, 300, 600) but I guess you know that already 🙂
I read your other thread on the 200 and the relay is one of the big issues on these models (200, 300, 600) but I guess you know that already 🙂
- Status
- Not open for further replies.