Help with Glensound power supply

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TapeOpAl

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Nov 6, 2011
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Just typed a big post and lost it all because my attachment was too big so I'll try and keep it brief.

Got a Glensound mixer in and the +ve rail of the power supply is only supplying half a volt compared with 18v on the -ve.

After checking with multimeter: transformer is ok, measured the voltage at the legs of the two transistors. The TIP146 on the (working) -ve side has ~24v on each leg and the TIP141 (non-working +ve side) has 20v on the middle leg and 0v on the other two. I guess I need to replace the 141?

I've reheated all the solder pads so I don't think it's a cold joint.

 

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sounds like a sensible thing to do, or maybe check the transistor first (desolder Tip 146 and check with multimeter)... but hey, you might want to put a 10 ohm resistor in series with the V+ as a 'thermo fuse'......

elektor magazine advised to do this on all power amps and it makes sense - if your fault is downstream you will not immediately blow your new transistor.....


- Michael
 
TapeOpAl said:
Just typed a big post and lost it all because my attachment was too big so I'll try and keep it brief.

Got a Glensound mixer in and the +ve rail of the power supply is only supplying half a volt compared with 18v on the -ve.

After checking with multimeter: transformer is ok, measured the voltage at the legs of the two transistors. The TIP146 on the (working) -ve side has ~24v on each leg and the TIP141 (non-working +ve side) has 20v on the middle leg and 0v on the other two. I guess I need to replace the 141?
Nah...  tip 141 is NPN transistor, middle leg is collector, so collector at +20v, base at 0v and emitter at 0v do not mean the device has to be bad. A good transistor could have those voltages.

Some other part or parts in the PS are the likely culprit.  An npn power pass transistor will have something feeding a drive voltage into it's base, roughly .6v more than output voltage should be.

 
I've reheated all the solder pads so I don't think it's a cold joint.

Could be open connection or part feeding the base of tip 141.

JR
 
C5 C7 shorted: lift one leg and see if voltage comes back.

R3 R2 R1 open: re-solder (don't just "reheat") their legs. No go? Take em out and replace.
 
PRR said:
C5 C7 shorted: lift one leg and see if voltage comes back.

R3 R2 R1 open: re-solder (don't just "reheat") their legs. No go? Take em out and replace.

Took out C7 and she's working so I'll replace that. Just for my own education, what's the purpose of c7 since it works without it?

Thanks so much for your (and everyone's) help.
 
> what's the purpose of c7 since it works without it?

Reduces humm/buzz.

It's a multi-stage buzz-filter. Think of a multi-stage water filter: coarse, medium, fine. One day no water comes out. Bypass the medium filter, water comes out-- the medium stage was clogged. It "works" without one stage, but it will work better with all the stages. I'm not sure your buzz-filter needs ALL that filtering, but a replacement C7 is only a dollar. (Beats heck out of these single-source final-filters I use for my drinking water--- $40 a pop at the cheap place.)
 
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