MEDIC ...replace output transistor pl400 had problem on DBT

[changdangnz]

I had replace all my output transistor and try to do a DBT. When i turn on power to do test light is bright so it is mean still short electrical on amplifer. Anyone can help me out this problem?

 

[laatsch55]

Post some pics of the output installation....

 

[changdangnz]

Lee , I just take photo all the new output transistor.let me know if you need more photo .

 

[laatsch55]

Have you run a collector to ground resistance cjeck?? That's collectors on the outputs...

 

[changdangnz]

Lee , How can I check it ?

 

[laatsch55]

With a voltmeter on ohms setting , one lead on ground the other on each output case.....

 

[changdangnz]

Lees , I found some is value is higher than 000.6 ohm. Then I just tight a bolt the. It stay at 000.6 ohm. Is that a correct value ?

 

[laatsch55]

No, that's almost a dead short...

 

[changdangnz]

But it is a new output transistor. I take a photo to let you have a look . Do I make a mistake

 

[laatsch55]

I would say you've made a mistake in mounting the outputs, and if you haven't, then there's another problem..

 

[changdangnz]

Do you think if a thermal base was on the leg tgen it will affect the output transistor ? If i tight the bolt to tight any affect ?

 

[laatsch55]

Did you use new mica insulators or sil-pads?

 

[laatsch55]

The bias transistor leads on the right channel look real sketchy, you need some heatshrink on those puppies. Also what do you have for bias transistors?

 

[changdangnz]

Yes. I was use a new silicon pad

 

[changdangnz]

Yes . I was order 2 new bias transistor.

 

[changdangnz]

Lee . On bias transistor legs i soldering with the lead.do u think it will affect short circuit

I don't understand, ........I know this, if the bias transistor is not wired correctly it will act like a short but so will 100 other things.

If you used sil-pads you did not need grease....

 

[laatsch55]

Well, I don't know how I managed to edit your post, but I did, sorry bout that...

 

[changdangnz]

Sorry Lee , I mean I use a clear plastic pad on output transistor. It is just like thin plastic

 

[laatsch55]

Yo Dennis!!! Could you link AK's transistor testing thread for Chang?? Can't figure out how to do it on my phone...

 

[NavLinear]

Yo Dennis!!! Could you link AK's transistor testing thread for Chang?? Can't figure out how to do it on my phone...

Sure:

http://www.audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/