Author Topic: my heater amplifier burned out ... replacement unit smoking ... short somewhere  (Read 1263 times)

cejpat

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Mercedes part number: 0008350157

old amplifier unit began smoking, burned out

tried to replace with remanufactured unit. that began smoking as soon as partially plugged in = pulled it off immediately.

what's going wrong?

anyone with a diagram?

i've got a replacement servo (3 years old) from George Murphy at Performance Analysis. He said possibly something broke in his servo = he's happy to test and see what/if anything wrong.

any ideas?

Euro_Sled

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did you ever figure out what the problem was with this?  I have a similar issue. 
1977 450SEL
1984 230CE

UTn_boy

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9 times out of ten it'll be because the servo has become stuck. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

Diesel 617

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and the remaining 1/10 times the Auxiliary water pump is burned out (its near the servo)

You can disconnect the Aux water pump and put a 9v battery to the connector and if you hear the motor then its good.

I'm starting to really believe that the upgraded aftermarket Climate Control kit is a good investment. Either that or pull a w126 system and fit it.
X3 1980 300SD Blown Heads, trans -Retired
1980 450SEL Parted out
1980 450SEL to Diesel Parted Out
1979 280SE Euro Spec Cloth Seats: Needs Rebuilt head and WUR
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Jed

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Hey Guys,

So if its not a stuck servo (tested with a 9 volt battery and the servo motor runs each way, open and closes)

and it s not a bad auxiliary pump (also tested with power to the leads and runs fine)

but yet one of the resistors on the amplifier keeps burning out as soon as the ignition switch is turned on (glows red hot and burns up)

any idea what else it could be?

1979 6.9, all stock.  system was working perfectly before rebuilt servo started leaking ,was sent back for re- rebuild and reinstalled.

thanks

jed
1979 Mercedes 6.9 #5206 - restored
1979 Mercedes 6.9 #6424 - ongoing restoration
1976 Mercedes 6.9 #484 - restoration?

UTn_boy

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The servo doesn't have to be stuck for short out the amplifier.  Unplug the amplifier and see if the resistor stops overloading. 

There could also be a dead short to ground in a power supply wire, and if so, then it'll merely be a matter of tracing the short down.  If you would like a schematic, I'm certain that one of us can supply you with that.  But isn't the schematic somewhere on the forum technical part?
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

Jed

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Thanks
Did you mean unplug the SERVO and see if the resistor overloads? the resistor is on the amplifier board.  I tried that and it does not overload if the 1-5 pin electrical plug on the servo is unplugged.

the rebuilder is telling me that if the motor in the servo works it should not be overloading??? I am skeptical at this point so glad to hear that it can still short.  I will pull a working servo from another car and plug it in and see if that doesn't fix the problem.  first I have to come up with some replacement resistors to solder onto my blown up amplifiers.... ::)

thanks again
1979 Mercedes 6.9 #5206 - restored
1979 Mercedes 6.9 #6424 - ongoing restoration
1976 Mercedes 6.9 #484 - restoration?

Malpaso44

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I live in Georgia and cannot survive without A/C. I replaced my servo a couple of times before I decided to purchase the upgraded unit. I haven't had any problems with the new system.
Some are born great, some achieve greatness and some have greatness thrust upon them.

UTn_boy

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Thanks
Did you mean unplug the SERVO and see if the resistor overloads? the resistor is on the amplifier board.  I tried that and it does not overload if the 1-5 pin electrical plug on the servo is unplugged.

the rebuilder is telling me that if the motor in the servo works it should not be overloading??? I am skeptical at this point so glad to hear that it can still short.  I will pull a working servo from another car and plug it in and see if that doesn't fix the problem.  first I have to come up with some replacement resistors to solder onto my blown up amplifiers.... ::)

thanks again

Yes, I meant unplug the servo, not the amplifier.  Sorry about that. 

If the amplifier quits shorting when you unplug the servo 1-5 plug, then it's either the servo or the Auxiliary electric water pump.  I believe you said you already checked the water pump, so that leaves the servo.  Try another servo and see what happens.  Just swap plugs to the test unit without mounting it. 

Regarding your amplifier, do make sure that none of the transistors have fried, as well.  If I remember correctly, the transistors are of the BR series, and are very common, cheap, and easy to find.  If in doubt replace them anyway. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

slfan

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I live in Georgia and cannot survive without A/C. I replaced my servo a couple of times before I decided to purchase the upgraded unit. I haven't had any problems with the new system.

Hello,

I am considering upgrading my Climate Control system.  Can you tell me what system you used for this upgrade?

Thank you,
1978 - 450SEL 6.9 - 3170
1978 - 450SEL 6.9 "Parts Car" - 2973

Malpaso44

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Some are born great, some achieve greatness and some have greatness thrust upon them.

slfan

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1978 - 450SEL 6.9 - 3170
1978 - 450SEL 6.9 "Parts Car" - 2973