Need Help with Monster Technics SA-1010 (stuck in protect mode)

Siraudio85

New Member
Hello, I'm new to the site and happy to be here. I recently acquired this monster receiver that powers up but stays in protect mode. When powered up no relays click. I understand this unit has a computer drive that controls the amp board and its very sophisticated. I need some help finding the problem that is making the computer go into protect mode.

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You’ll want a multimeter set to a DC volt range that will read to 70V

Connect negative lead to ground.... with amp on check for voltage at TP2 then TP4.... both should be 0V

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You’ll want a multimeter set to a DC volt range that will read to 70V

Connect negative lead to ground.... with amp on check for voltage at TP2 then TP4.... both should be 0V

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Thank you so much! I saw your avatar and immediately realized I’m getting help from a Technics pro. I did just as you said and I’m getting 0 at TP2 but I’m getting 68.7 volts at TP4!
 
Do check for. Collector-Emitter shorts on Q624, Q626 Q628 & Q630

If they’re not short... what voltage is at the Collectors of Q616 and Q618 ⚠️ Careful not to slip/short anything ⚠️

Should see +(616) or -(Q618) 1.8-2V
 
Pulled blown resistor. It is completely open. Since it’s a control resistor this could be the cause of high voltage right? Could it’s failure have also damaged the transistors or is there a chance they are fine? I’m sorry I’m not sure how to check them. I will look that up, I was told the only sure way was to pull them and test them out of the board but I don’t wanna do all that yet.
 

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Yeah, 2 outputs for each channel seems to be pushing the design. My Luxman L-430 105 wpc) uses 4 devices per channel.
 
It's more likely a failed transistor burned that resistor. I'd pull the transistors from the bad channel and measure them. Be very careful of that thermistor (the yellow blob in one of your pics) is is likely to be very fragile and hard to replace.
 
Ok check also Q620 & 622

Replace R666 (1/2W 330)

Check Synchro Bias diodes D13,615,617&619 (OA90) And Stabistor diodes D621 & 623 (MA27W-A)’

⚠️ Check TH602 (10K) - make sure it is not open circuit! (Resistance may vary temp based)

Check also R656 (82K) and R654 (1K)
 
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It's more likely a failed transistor burned that resistor. I'd pull the transistors from the bad channel and measure them. Be very careful of that thermistor (the yellow blob in one of your pics) is is likely to be very fragile and hard to replace.

Yup there was a ‘tug of war’ over that resistor....

Hopefully thermistor is not affected.....
 
Yup there was a ‘tug of war’ over that resistor....

Hopefully thermistor is not affected.....

This is what I got so far. I can’t check the transistors because I don’t have a transistor checker and I’m not entirely sure how to use the DMM to check them. Should I just try to find them and replace anyway?
Having some issues finding parts like the TH602
 

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On all transistors in that pic.... check for short circuits between pins 2 and 3

Driver transistors replace with 2SA1930 and 2SC5171
Output transistors 2SA1494 and 2SC3858
Diodes OA90 - (if available) or 1N60 Germanium
Is that thermistor open circuit?
 
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On all transistors in that pic.... check for short circuits between pins 2 and 3

Driver transistors replace with 2SA1930 and 2SC5171
Output transistors 2SA1494 and 2SC3858
Diodes OA90 - (if available) or 1N60 Germanium
Is that thermistor open circuit?
Yes, the thermistor is open and has a burn hole in it. It blew up good!
 
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