The rectifier is typically a 20 to 30 amp rated at 100 PIV. You can
disconnect the leads and measure it as 4 diodes using an ohm meter. It its
good then no replacement is necessary. Lift the crowbar zener and see what
happens. DO NOT HAVE A RADIO CONNECTED as the voltage regulator may be
pushing out 20+ volts. Use some type of resistive load on the output and
measure the voltage. If the voltage is high then there may be a problem on
the regulator board. Thus the crowbar is doing its job. If lifting the
crowbar diode and then you find the voltage is normal at about 14 volts,
then you can suspect the crowbar device is defective.
It's a basic 723 linear regulator circuit with overvoltage protection.
Basic cookbook circuits.
Again, don't connect a radio until you are sure the power supply has about
14 volts output and is regulating. This can be done by using a load vs. no
load condition. I use a 10 ohm 100 watt resistor for my power supply tests.
73
Bob, K4TAX
----- Original Message -----
From: "Randy Fulco" <rfulco@bellsouth.net>
To: <tentec@contesting.com>
Sent: Monday, February 04, 2013 10:21 PM
Subject: [TenTec] Help wi TT 280ps
The full wave bridge from the transformer is labelled VARO207T. Does anyone
know what that would sub to? Yes, know many might work, but anyone had
experience here? The output is shorted, upon turn on- the lamp flashes, goes
to overload, meter show it drawing 5A, and pass transistors start heating up
and they would self destruct if left on. Suspect the crow bar zener bad,
1N966. Pass transistor both ohm out ok, and both heat up the same. Any
thoughts?
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