Drake PS7 power supply WORKING correctly on two 2N5301 pass transistors! May 11, 2023
Well the 4th day working on the PS7 is a charmer.
I figured start with basics.
Will the TIP31 transistor drive the 4 2n5303's to conduct and go to VCC which is about 20V?
NOPE.
Well then.
Pull the regulator chip off of the board (I socketed it) and drive the base bias on all 4 2N5303
pass transistors with a 68K resistor off of VCC which is 20 volts.
Did that work? Well the voltage went up a few volts.
Nope.
Well then PULL out the 2N5303's. Disconnect two of the remaining 2N5303's.
Insert old 2N5301 NPN transistors which still look to work...
Running on two pass transistors and..
It works!
So I need to get two more 2n5301's and an insulator for the TIP31 driver transistor to seat that
back on the chassis which is the heatsink and back in business?
Maybe.
I believe the problem to be a bad ground to the regulator board.
The regulator board has its own power supply on it and the huge power transformer
has separate windings for this power supply.
Has a full bridge rectifier on it.
VCC from this supply - about 30 volts.
Moral of the story?
Bizzaro things CAN and will go wrong.
Test everything starting at basics.
VCC coming and going?
Yep it was a bad ground as the regulator board comes in on stick pins - same as inside the
TR7 and same as the Heathkits too.
QED.
Once I get more parts then fit them in and see how things go.