Luxman RX-101 gets short when i plug Left channel speaker

FRANKPIETTE

FRANKPIETTE

Member
Hello all

I just recapped a ''Suckface'' Luxman RX-101 receiver, it also had a shorted output transistor, i replaced all 4 O.T.
So i tested it on DBT for first ''power on'' everything so far was looking good, I turned it off, and plugged my speakers. Turned it on again when i pressed the power button, got a big short on DBT. I changed my cable and use another pair of speakers that played on other gears i have. Still got the short on Main Left, and Remote Left too. i depressed the A and B speaker switches, short disapeared.

So left channel shorts happens when i plug left channel speaker only, with no source plugged in. No shorts when i only plug the right channel Main or remote.

Anyone had that exact same problem before when pluggibg speakers? Any help woud be really appreciated, Right channel plays very well no shorts.
 
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Is it the same problem you had before the cap and output transistor replacement?

Can you take some voltage measurements of the outputs (on DBT) and post them?
 
Dave1027 said:
Is it the same problem you had before the cap and output transistor replacement?

Can you take some voltage measurements of the outputs (on DBT) and post them?
Click to expand...
Hello Dave, no another receiver, i will take volatges at soon as i get the new trim pots. 4 new OT. No shorts until i connected the speaker on that channel. The other channel ok.
 
If there is a short with either main or remote plugged in and the short disappears when you press both main and remote switches with only one set of speakers connected, that means the main and remote are in series with two sets connected. Pressing both switches with only one set connected, of course removes the short.

The thing to remember is that there is only one output amp. for each set of main and remote speakers. There are not separate amps for each.

Doug
 
Dave1027 said:
Is it the same problem you had before the cap and output transistor replacement?

Can you take some voltage measurements of the outputs (on DBT) and post them?
Click to expand...
Hello Gentlemen, i just measured 78 VDC on (circled) Q114a (Q113a on pcb brd.) output transistor, doesn't even heat up.??? I took voltages from all 4 O.T. BCEz, the 3 other Output Transistors had similar low voltages when i measured B to C, B to E etc. 78V that's lot of volts. New trimmer pots are not installed yet. Close/around 0 vdc on all 4 speakers Main LR Remote LR connectors. With both speaker switches pressed On. No source, no speakers connected
 

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The rails are plus and minus 42 volts. That's probably where you are getting your 78 volts. Connect your ground lead to ground. Then measure C, B and E separately of Q112 and Q113.
 
The service manual I'm looking at says Q114 and Q115 are not installed in the RX-101. It shows them for the RX-102. Those must be paralleled outputs for the higher powered model.
 
Dave1027 said:
The rails are plus and minus 42 volts. That's probably where you are getting your 78 volts. Connect your ground lead to ground. Then measure C, B and E separately of Q112 and Q113.
Click to expand...
Exactly, Since on Var/DBT, i have 39V at each main filter caps, as for Q112 and 113 according to schematics? or what's printed on the pcb board (error in SM)? Thanks !
replaced all 4 tranz on both channels, nevermind the measures i took earlier, while take again soon. Q112 and Q113 i got positive approx 39vdc on all C,B,E so 6 times around 39Vdc...???
 

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Ok back at the RX-101, here are the volatges i got few minutes ago Variac at 95V, it's terrible lol.
 

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Q112a for sure is blown. Try removing or disconnecting both Q112a and Q113a and then reading the volts on driver transistors Q110a and Q111a.
 
Dave1027 said:
Q112a for sure is blown. Try removing or disconnecting both Q112a and Q113a and then reading the volts on driver transistors Q110a and Q111a.
Click to expand...

Thanks Dave, i removed Q112a and Q113a and at 95V on Variac again, volts on driver transistors Q110a and Q111a

Q110a E: 27 B: 28 C: 25V
Q111a E: 25 B: (-28) C: 25,5V
 

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Dave1027 said:
Are you ordering exact replacements? If they are substitutes then you will need to replace both outputs and both drivers.
Click to expand...
Not the exact part numbers, all substitutes. The outputs were not paired, one side had equivalent NPN PNP on one side. So they were replaced years ago, i guess.
 
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Dave1027 said:
Looks like Q110a is blown too.
Click to expand...
Both Q110a, Q111a are good, tested them out of circuit board. Replaced all 4 Output transistor, I get the same voltage 20+Volts (approx.) on all feet of Q110a-111a -112a-113a as before i changed them, i'll test upstream today to isolate the part that's ''open'' ? We'll see! H.A.N.D.
 
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