Sony SLV 615 VCR - Power Supply Problems
Tony Narkowicz
I'd appreciate any help anyone can offer in repairing my trusty old Sony
Video.
Model: SLV 615
Age: Approx 1991
Power Supply type Mitsumi SR345
Suspected Problem: SW9V regulator section
It failed recently after re-connecting to the mains. I automatically
assumed power supply troubles, and checked the power supply. The only
obvious failed component is Q205 (NPN), which is the first transistor in the
SW9V power circuit, accepting an input directly from the "Power Control"
line which then drives a second stage, Q203 (PNP) which then drives a 7809
9V voltage regulator.
I am still waiting on a genuine Sony Part replacement for Q205, which is a
"N4211" device. Can anyone advise of an equivalent replacement?? The Sony
part will take a few weeks to arrive, so in the mean time, I have tried a
few small NPN devices to try the get the VCR working again. I have also
replaced most of the electrolytics on the power supply. Some things to
note:
All main power rails, except the SW9V and SW5V on the supply are OK, ie +6V,
+35V, M12V, 12V, -30V and +2.5 V. I have tested all these rails under load
and they are OK. However, the power supply only provides these rail
voltages if I disconnect the "Power Control" line which comes from another
major board somewhere. Without disconnecting "power control" the power
supply shuts down after about 1 sec.
With some fiddling with the gain of Q205 (placing a 2Mohm resitor in series
with the "power control" input to the base, I can keep the power supply
alive with "power control" connected, and the unit sort of works. It plays
just OK, but does not record. I've noticed that the tuner loses channel
tune when the record button is pressed, and it appears to be associated with
voltage drop somewhere. Furthermore, the "SW9V" power rail loses
significant voltage when I hit the record button, so I assume the "SW9V
supplies the tuner and it is failing under load. I load tested it
separately and confirmed this. I have replaced all semiconductors associated
with the SW9V circuit, but still no luck (but I still need to try the
genuine Q205).
How do the "power control" and "SW9V" circuits interact? Is the SW9V a
constant voltage output rail, or is it some kind of servo output, regulated
by the pulse widths or pulse amplitudes on the "power control" line? What
are the normal operating voltages of the SW9 rail, under no load, and
recording load conditions.
Any other hints on this one??? Any other test measurements I should make?
Please reply to group, or to tnark...@primus.com.au
.
Jerry G.
ESR over the years. Using an ESR meter to check the caps or replacing
all of them at the same time is the best test for the caps. This is
because a number of them can go bad at the same time. This is the more
expensive method, and will usually fix the supply.
As for the transistor you are waiting for, did you check it properly
with the diode check position on your DVM to see if its junctions are
shorted or opened? After it passes the diode check, the best check is
to also use an HFE meter to see if it has proper gain.
--
Greetings,
Jerry Greenberg GLG Technologies GLG
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