Need to get MG Electronics Power Supply repaired...or NOT!?

7812 voltage regulator test results:

w/ Power off and writing facing me

Black lead on the center pin, read lead on the left pin = 1.2mV and it trickled down to 0

Black lead on the center pin, read lead on the right pin = .5mV and it trickled down to a negative number

w/ Power On and writing facing me

Black lead on the center pin, read lead on the left pin = 30V

Black lead on the center pin, read lead on the right pin = 12.04v

I re-tested the D313 for continuity (after the unit has been turned on and off)

There is NO continuity between the base and the emitter or collector

There IS continuity between the emitter and the collector

I retested the corroded diode and it is ok.  The corrosion was giving me a bad reading previously but I scraped it off and the diode shows a voltage reading of .519v in one direction and nothing in the other.

7812 voltage regulator test results:

w/ Power off and writing facing me

Black lead on the center pin, read lead on the left pin = 1.2mV and it trickled down to 0

Black lead on the center pin, read lead on the right pin = .5mV and it trickled down to a negative number

w/ Power On and writing facing me

Black lead on the center pin, read lead on the left pin = 30V

Black lead on the center pin, read lead on the right pin = 12.04v

I re-tested the D313 for continuity (after the unit has been turned on and off)

There is NO continuity between the base and the emitter or collector

There IS continuity between the emitter and the collector

I retested the corroded diode and it is ok.  The corrosion was giving me a bad reading previously but I scraped it off and the diode shows a voltage reading of .519v in one direction and nothing in the other.

All sounds good and normal except the D313. We need to test that one out of circuit and verify if it is good or bad.

At some point I mistyped Read when I meant to type Red. I mention it so that we don't start a new convention for what is the correct nomenclature.  Sorry about that. I always try to proofread but at 1:30 AM I may miss things.

John

I am going to order a replacement,  according to the data sheets, the NTE152 is similar but has different voltage (90v min and max) while the D313 is 60v min and max)

Does that make a difference?

Thanks,

Matt

I ran another test with the D311

With my multimeter set to the diode tester...

With the negative lead on the base, I get no reading touching the emitter or collector

With the positive lead on the base, I get a .578 reading touching the middle pin

With the positive lead on the base, I get a .580 reading touching the right pin

I ran another test with the 2N3055 NPN power transistors

With my multimeter set to the diode tester...

When either the negative or positive is on the base (blue), I get a reading that starts out .03 and rises to 1V between the base and both the collector (red) or the emitter (yellow)

When either the negative or positive is on the collector, I get a reading of about .010 V between the emitter

This is actually an improvement. Go for it.

John

You say D311 is this a different transistor from the D313?

The readings that you listed for that D311 sound like a good transistor.

I don't think the diode tester is doing a good job on the 2N3055 s  while in the circuit. If you can get the covers off and take out the two retention screws they should just unplug from their sockets. Then try to run the diode and continuity test again.

John

Sorry, that was a typo.  I retested the D313 and got those readings.

But I ordered a new D313 (now a NTE152)

I put it in when it gets here and get back to you.  If it doesn't fix it then I'll work on the 2N3055s

Sounds good , let me know.

John

I got the NTE152NTE152 transistor in and it tests exactly the same as the pulled D313 transistor.  So I'll put in the new NTE152NTE152 and pull the power transistors to test next...

New Transistor

No Continuity between any pins

Continuity between middle pin and backboard

With positive on pin 1 and negative on pin 2 = .578 V

With positive on pin 1 and negative on pin 3 = .580 V

Old Transistor

No Continuity between any pins

Continuity between middle pin and backboard

Continuity between middle pin and backboard

With positive on pin 1 and negative on pin 2 =  .580 V

With positive on pin 1 and negative on pin 3 =  .585 V

Still a no go for Voltage