[TenTec] Help wi TT 280ps

[Bob McGraw - K4TAX]

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 at bellsouth.net>
To: <tentec at 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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