[Kenwood] PS-53 on strike

[Peter Ravn]

Thanks for the answers. Despite the following measures the voltage on the 
output terminal is 21.4 V instead of 13.8 V. Turning VR1 (power adjustment) 
has no effect.

1) Q5 sitting close to thermistor TH1 seemed to have melted and fused with 
TH1, which was covered with sticky white powder. Transistor and thermistor 
were replaced with no effetct..
2) Q1 and Q2 were tested out of circuit. Q2 was found faulty, and both 
transistors were replaced with no effect.
3) Q4 was tested out of circuit and found OK.
4) Diode D4 tested and found OK. Replacing it had no effetct.
5) Voltages on Q1 and Q2: C 22.7, B 22.1, E 21.5
6) Voltages on Q4: C 22.3, B 21.4, E 21.5
7) Voltages on Q5: C 21.3, B 20.4, E 20.2

Conclusion? The voltage reguator circuit doesn't work. But why doesn't it?

Thanks in advance
OZ8CTH
Peter

----- Original Message ----- 
From: "Avi on 7510" <tiavi at bezeqint.net>
To: "Peter Ravn" <fasan5 at privat.dk>; "," <kenwood at mailman.qth.net>
Sent: Monday, May 03, 2010 4:48 PM
Subject: RE: [Kenwood] PS-53 on strike


Hi Peter,
There must be a power supply virus going around - yesterday I posted about 
my PS50 quitting.

I'm assuming the PS53 is also a linear supply.
The 19v you mentioned sounds like the output from the bridge rectifier, 
before the pass transistor(s? - I'm not familiar with the PS53 circuit 
diagram), and the slow decrease in voltage sounds like normal behavior for 
smoothing capacitors with a bleed resistor across them for safety - they can 
pack quite wallop for quite a while without a bleed resistor. It sounds like 
the regulator circuitry may be faulty, or perhaps the pass transistors 
themselves?

Just a semi-ignorant guess....

Avi 4X6UA on htc advantage 7510

-----Original Message-----
From: Peter Ravn <fasan5 at privat.dk>
Sent: יום שני 03 מאי 2010 13:21
To: Kenwood at mailman.qth.net
Subject: [Kenwood] PS-53 on strike

Without warning my otherwise reliable PS-53 died the other day: no 13.8 V on 
the output terminals. The fuse was ok, so the board was inspected. Q5 
(2SC2458) sitting close to thermistor TH1 seemed to have melted and fused 
with TH1, which was covered with sticky white powder. Further inspection and 
internet research proved that Q5 and TH1 are covered with a piece of shrink 
tubing to keep them in close contact with one another. I replaced the 
transistor and cleaned and checked the thermistor, which measured 2.4 KOHM 
with falling resistance by increasing temperature.

Still no voltage on the output terminals. But when the power switch is 
turned and off,  there are 19 V on the terminals falling slowly to zero, 
which might give the experts on this thread an idea where the fault is.

Thanks in advance
OZ8CTH
Peter
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