700B blew one Right channel 5A supply fuse

[Zach C.]

Gary, anytime there is a reading of .00 accross any semiconductor jct that is a redflag. Pull Q1 and check out of circuit. It should never read short between any n2 test points, same with Q3, but we're gonna go one at a time here...

Whoops. I mis-read Gary's 00 as a OL typo, since my meter always shows the volt drop due to lead resistance.

...and I totally missed it in his first post. The one on Q1.

My bad.

 

[Zach C.]

WHOA!!! Way to generic to apply to all tranny connections. When posting that Gary, please state what tranny you're talking about and in what position...

I think this was referring only to Q3, since I suggested (wrongly it seems) that Gary may have inadvertently mixed up his BCE connections between the two Q3s he tested.

 

[laatsch55]

Zach, I don't think that was wrong as I often assume too much in this long distance helping, please keep following along, I certainly miss things. Hopefully with all of us we won't...

 

[Zach C.]

Zach, I don't think that was wrong as I often assume too much in this long distance helping, please keep following along, I certainly miss things. Hopefully with all of us we won't...

A common error is still an error, but I feel ya.

 

[laatsch55]

 

[62vauxhall]

WHOA!!! Way to generic to apply to all tranny connections. When posting that Gary, please state what tranny you're talking about and in what position...

Yes, thinking back to your explanation of transistor pinout, I did transpose E & C checking Q1 in circuit, but I'm fairly sure I installed them correctly.
Before seeing this post, I removed Right channel Q1 TSI-97 and checked out of circuit.

Q1 TSI-97
OL - red to base & black to E
OL - red to base & black to C
.66 - volts red to E & black to B
.66 - volts red to C & black to B
OL - red to E & black to C
OL - red to C & black to B

Viewing the top of the board, this is how I mounted transistor Q1. Would you suggest re-installing it and performing all suggested transistors checks again? If it would help, I can likewise diagram the other transistors in question to determine if they are oriented on the board correctly.

I must leave shortly to help someone with a fencing project so probably cannot return to this until later this afternoon.

 

[laatsch55]

Q1, Q2 have their emitters tied together with a short trace, is that how they are now?

 

[laatsch55]

Yes, thinking back to your explanation of transistor pinout, I did transpose E & C checking Q1 in circuit, but I'm fairly sure I installed them correctly.
Before seeing this post, I removed Right channel Q1 TSI-97 and checked out of circuit.

Q1 TSI-97
OL - red to base & black to E
OL - red to base & black to C
.66 - volts red to E & black to B
.66 - volts red to C & black to B
OL - red to E & black to C
OL - red to C & black to B

Viewing the top of the board, this is how I mounted transistor Q1. Would you suggest re-installing it and performing all suggested transistors checks again? If it would help, I can likewise diagram the other transistors in question to determine if they are oriented on the board correctly.
View attachment 14363
I must leave shortly to help someone with a fencing project so probably cannot return to this until later this afternoon.

That transistor is fine...We'll be here..

 

[62vauxhall]

When I get back later I'm going to diagram the board anyway. I'll post it first but I think it would help to have a "map" to follow as I recheck those transistors. The space I have to work on the amp is too small for me to lay the pages I've accumulated. Some are on my desk, some on the dining room table and I've been going back and forth to reference them. I can see such a "map" being useful to avoid further mistakes.

 

[laatsch55]

Amen.....

 

[62vauxhall]

Q1, Q2 have their emitters tied together with a short trace, is that how they are now?

Yes, And will be again when I re-install that Q1.

 

[laatsch55]

Good....

 

[62vauxhall]

Crude though it may be, here is that diagram of transistors Q1 through Q4 as I have placed them on the board and to the best of my understanding, their pinouts.

If this is correct, please advise and I shall flip the diagram over to correspond with the underside of the board so I can re-check these transistors and post revised results.

I must be gone again for about 4 hours but will look for follow up as soon as I return.

 

[laatsch55]

Looks good..

 

[Gepetto]

Crude though it may be, here is that diagram of transistors Q1 through Q4 as I have placed them on the board and to the best of my understanding, their pinouts.

If this is correct, please advise and I shall flip the diagram over to correspond with the underside of the board so I can re-check these transistors and post revised results.

I must be gone again for about 4 hours but will look for follow up as soon as I return.

View attachment 14370

What type control board do you have in this amp? Your diagram does not look like a PL20 board which was common in most PL700Bs

 

[laatsch55]

14A Joe..

 

[Gepetto]

14A Joe..

Most 14s have one of the transistors turned 90 degrees in the front end section. Not like this diagram.

 

[laatsch55]

Yep, a rare variant that Ed has talked about also...the 14 blank in my possession is tutned 90 deg also....I have seen the ones like Gary has....

 

[62vauxhall]

In the process of re-installing Q1, I knocked off the emitter's trace hole. I used a jumper from the emitter leg to a resistor connection that the trace led to. Seems to be OK but is it accepted practise to hook a transistor into a circuit when it's not mounted on the board?

These are the revised in circuit readings for Q1 through Q4. If 00 (zero zero) is a red flag, that's what I got between Q1's emitter and collector in both directions.
Also there's voltage in one direction only between the emitter and collector at Q3.

Q1
OL - red to base & black to emitter
OL - red to base & black to collector
.66 volts - red to emitter & black to base
.66 volts- red to collector & lack to base
00 volts - red to collector & black to emitter
00 volts - red to emitter - black to collector

Q2
OL - red to base & black to emitter
OL - red to base & black to collector
.67 volts - red to emitter & black to base
.66 volts- red to collector & lack to base
OL - red to collector & black to emitter
OL - red to emitter - black to collector

Q3
.65 volts - red to base & black to emitter
.65 volts - red to base & black to collector
OL - red to emitter & black to base
OL - red to collector & lack to base
.81 volts - red to collector & black to emitter
OL - red to emitter - black to collector

Q4
.61 volts - red to base & black to emitter
.59 volts - red to base & black to collector
OL - red to emitter & black to base
OL - red to collector & lack to base
OL - red to collector & black to emitter
OL - red to emitter - black to collector

 

[laatsch55]

Gary, the traces are shit and pretty easy to lift....whatever it takes to fix em. I usually lay a cut off resistor lead and bend it in the same shape as the trace and solder it in a place or two to the old one.

Is this the left or right channel?