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New member. Help with M500T


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Hello all.  I recently acquired some carver gear. An M500t amp and a TFM 35 amp.   Looking for some direction on the M500.  I understand it’s a dual voltage unit using low and high voltages on the rails.  My issue is the relay doesn’t close upon power up.  I’m leaning toward the op amp or something in that circuit.  All the rectifiers check out good but I’m only getting around 30v on the low V side.  Not the 40v it’s showing in the manual. 
The relay is good as I have supplied 24v to the coil to test it.  I know these amps are different than most I’ve worked on but I’m ready to tackle this one.   Thanks in advance for any input and I look forward to interacting with all of you.    Cheers.  

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if the relays are not engaging, your amp is likely in protection.  Something has gone wrong.  Suggest you start with downloading the service manual.  Check the output transistors for shorts.  Also check for DC offset at the outputs (up stream from the relays).  This may help narrow down why its going into protection.

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Welcome @BigB, glad you found us!  Keep us posted as you put your 500 back in service.  

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Checked MV at TP 3,4.   Have 5.1v.   VR 102 had no effect.   Should be around 6mv.   Looks like an issue to me 

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I checked all of the output transistors Q119-126 as well as Q118,119,109,110,116,117.  All test good 

 

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TP3 or TP4 to ground is 5.1vdc.   TP1,2 to ground is 100mvdc.   I checked all of the outputs and they test fine.   I’m thinking another transistor on the board ?

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Gonna do some more testing on this M500t.  I found several bad resistors and replaced them it there must be a reason they failed.  Looking at transistors now and found Q116,118 shorted.   My main voltages look good (42 and 74v ) from the power supply.   This is a way different amp than I’m used to.   

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  • 4 weeks later...

Update on the M500t.   Replaced several transistors in this unit and recapped it.   Also changed out some toasted resistors.  DBT indicates no shorts but still no speaker relay.   I’m also getting some odd voltages from the transformer. Can you test these V from chassis ground or transformer center tap(black wire) ? The circuit to D601 is only reading around 5.7v a/c.   D601 is outputting 21.5vdc.  That is checking + to - with a meter on dc.    

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  • 3 weeks later...

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