Kenwood VR-407 receiver problem

[Dan Draeger]

My receiver powers on for about 5 seconds then clicks off. It seems
that the relay next to a transformer near where the power comes in is
turning off. There is current flowing through at first and when it
clicks off there is no current on the other side. How can I
troubleshoot this? Seems like maybe something in the output stage
went. I took it in to the shop and they wanted $170 to repair it.
Thanks for any pointers.

[CLSNOWYOWL]

Other than mentioning that you must check out the appropriate web sites for all
of the safety procedures and troubleshooting techniques involved in order to
repair this device, please read the lengthy post that follows.

I have worked on a few of these. The major problems with Kenwood eq's and amp's
(other tha with the standard output problems) that I have generally contended
with were the drive and bias tranistors failing, causing either a partial power
failure or total power failure.

There is a current limiting resistor in line with the collector of the
transistor. When the resistor failed, the resistor would cause the bias
transistor to short out from collector to emitter and sometimes, the electronic
failure would travel downline to the drive transistor that would turn on either
to voltage regulator IC and/or the system control IC depending on how the
circuit was designed. My solution I found that worked to correct this
overcurrent condition was to put in a higher value resistor to resist the
current (kept the voltage rating and wattage about the same) and to check for
any overload o the DC offset when adjusting the bias voltage. All devices I
have spoken of were PC mounted, not surface mount components.

These were very difficult problems to tackle in the troubleshooting
procedures and I found these systems to be particularly challenging to repair.
For the tech., it is one of those frustrating situations where you check out
everything else and then finally find that problem to be the cause of the
failure. it is one of those devices that make you see, "Good! Finally found the
cause of the problem! Whew!" My first one amp of that series I troubleshot took
me six hours to diagnose accurately.

So, I hope this advice saves you alot of time.

Good luck and happy holidays

Charles Lucas

Subject: Kenwood VR-407 receiver problem
From: ddra...@umich.edu (Dan Draeger)
Date: 11/22/01 4:12 PM EST
Message-id: <a6464cfc.01112...@posting.google.com>