700B blew one Right channel 5A supply fuse

[jbeckva]

With red to fuse holder black to bus bar - 0 OL
With black to fuse holder red to bus bar - an unsteady 51 K Ohms.

Try the measurements at the points in the pic above... you will be taking FOUR measurements, reversing the leads between each point above and ground..

positive lead.. positive rail.. negative lead ground

negative lead... positive rail.. positive lead ground

positive lead .. negative rail... negative lead ground

negative lead.. negative rail.. positive lead ground

One FINAL thing... for each of the four measurements above, and the leads in the same position, measure the DC volts FIRST. If you see ANY of these voltage measurements exceed even a quarter of a volt, STOP and let us know.

 

[62vauxhall]

See pic... measure at these two points to ground, and between these two and the right channel positive output terminal. And again - with the right channel fuses pulled.

View attachment 14940

With black to bus bar ground and red to positive rail - OL
With black to bus bar ground and red to negative rail - 5.82 M Ohms.

Between right channel positive rail and right channel positive output - 620 M Ohms
Between right channel negative rail and right channel positive output - 1.62 K Ohns

 

[jbeckva]

Try the measurements at the points in the pic above... you will be taking FOUR measurements, reversing the leads between each point above and ground..

positive lead.. positive rail.. negative lead ground

negative lead... positive rail.. positive lead ground

positive lead .. negative rail... negative lead ground

negative lead.. negative rail.. positive lead ground

One FINAL thing... for each of the four measurements above, and the leads in the same position, measure the DC volts FIRST. If you see ANY of these voltage measurements exceed even a quarter of a volt, STOP and let us know.

Bumping this post here in case you missed it. Also, would you be able to take a picture.. about at the same angle and aspect as mine.. but a little "wider" so I can see the connections to the driver board?

 

[62vauxhall]

Measurements at the points indicated.

positive lead.. positive rail.. negative lead ground - minus .005 volts and OL with meter at ohms setting

negative lead... positive rail.. positive lead ground - minus .018 volts and OL with meter at ohms setting

positive lead .. negative rail... negative lead ground - minus .047 volts and OL with meter at ohms setting

negative lead.. negative rail.. positive lead ground - minus .08 volts and OL with meter at ohms setting


I thought my recently acquired DMM set itself to the range it was expected to read at and had wondered why it display mv as opposed to volts and megohms vs k ohms, It also has auto shut off which really pisses me off because when I next turn it on, it could be giving me a different range. For this test, I used the range button to have it display in volts and ohms and above is what I got.

If I should re-take these measurements with the meter set differently, please advise.

Photo(s) as requested.

 

[62vauxhall]

Apologies if my replies have been slower that usual. An older acquaintance of mine passed away this morning and I've been getting a lot of calls. He was sort of a "life coach" and a lot of people got to know each other through him.

 

[jbeckva]

Apologies if my replies have been slower that usual. An older acquaintance of mine passed away this morning and I've been getting a lot of calls. He was sort of a "life coach" and a lot of people got to know each other through him.

No problem...

The 2nd pic is about right as far as where I'd like to look. Can you move the signal wires coming from the inputs out of the way - enough for a clear pic on the board connections?

Also ... I noticed where you have two screws across the top of the sockets - one for each side pos and neg. Are there transistors and insulators on the other side of those screws. Just making sure.... Measure from each screw point that is in the pic, right to the MIDDLE tab of the 3 tab terminal strip, right below the thermal cutouts. Resistance... two measurements.. one for each screw on the top.

 

[laatsch55]

Good eye Jer....

 

[jbeckva]

For this test, I used the range button to have it display in volts and ohms and above is what I got.

Please leave it in auto range (goes to that setting as you switch from ohms to volts)... repeat the four measurements here. Resistance / ohms only.

 

[62vauxhall]

No problem...

The 2nd pic is about right as far as where I'd like to look. Can you move the signal wires coming from the inputs out of the way - enough for a clear pic on the board connections?

Also ... I noticed where you have two screws across the top of the sockets - one for each side pos and neg. Are there transistors and insulators on the other side of those screws. Just making sure.... Measure from each screw point that is in the pic, right to the MIDDLE tab of the 3 tab terminal strip, right below the thermal cutouts. Resistance... two measurements.. one for each screw on the top.

Those screws are what mount the RCA 410 transistors which are in place with sil pads beneath them. Placing the black meter lead to the middle tab of the terminal strip (chassis ground) and with the red lead to the screws, the meter in ohms position displayed OL in all cases.

I replaced the original signal wire due to a detected short and what I wound up using was more substantial that what the factory used. I could not really move it out of the way for a better picture so I disconnected it. Too bad though because the right channel pads the lead was soldered to have come away from the board. I'm going to have to ponder a way of fixing that. Not much tensile strength in that trace material

 

[jbeckva]

Those screws are what mount the RCA 410 transistors which are in place

I see screws on both sides.. the two at the top, and from what I can tell I don't see the transistor pins sticking out. What's on the other side of the two screws below?

 

[jbeckva]

What do you get for resistance between that center tab and the main caps buss bar?

 

[62vauxhall]

I see screws on both sides.. the two at the top, and from what I can tell I don't see the transistor pins sticking out. What's on the other side of the two screws below?

View attachment 14951

Those are also output transistor mounting screws but there are no transistors therefore no sil pads.

Is this where the light goes on?

Some time ago, instructions were to put output transistors back in place but had to remove them again shortly thereafter.

Because the rows of transistor sockets or the heatsinks were not secure and I was concerned with them shorting or breaking. My infinite wisdom dictated securing the rows both top and bottom, ergo since an RCA 410 was screwed onto one end of each row, there should be a screw at the other end to keep the rows stationary. .

I am now anticipating being told those uninsulated screws are and have been the cause of the problem.

 

[jbeckva]

Those are also output transistor mounting screws but there are no transistors therefore no sil pads.

Is this where the light goes on?

Some time ago, instructions were to put output transistors back in place but had to remove them again shortly thereafter.

Because the rows of transistor sockets or the heatsinks were not secure and I was concerned with them shorting or breaking. My infinite wisdom dictated securing the rows both top and bottom, ergo since an RCA 410 was screwed onto one end of each row, there should be a screw at the other end to keep the rows stationary. .

I am now anticipating being told those uninsulated screws are and have been the cause of the problem.

Well.. yeah. But that's ok we all have to learn sometime (should have seen the first time I attempted to work on these beasties... it was not pretty!)

If you are concerned about the rest of the sockets flying around, I'd say go ahead and put in four of the outputs with the insulators across the top, making sure first that each of the four you've done the "once over" check with the diode check function like Lee showed ya earlier. Then... double and triple check yourself.

Once that's done, repeat the slow powerup test... all fuses in.. go for it! If the bulb remains dim after that, we be in business..

 

[jbeckva]

ps.. That's also why my 2nd WOPL build ever carries this title... LOL.

http://forums.phxaudiotape.com/show...00-Round-2-it-s-quot-Personal-quot-this-time)

Came off from a 10 year hiatus working on this stuff... Learned the hard way how rusty I was, heheh.

 

[jbeckva]

One more thing to check... when you get the top row filled, double check all four fuses. Logically neither channel should have allowed the amount of current draw that would take your rails down to 6 volts.

 

[laatsch55]

If there was a dead short to the collector bus bar....yep.... At 40 or 60 volts through a DBT, very possible..

 

[62vauxhall]

One more thing to check... when you get the top row filled, double check all four fuses. Logically neither channel should have allowed the amount of current draw that would take your rails down to 6 volts.

All four fuses are good.

As suggested, I put in a top row of output transistors and sil pads then checked that top row as well as the RCA 410's.

Before I go to applying power, I measured them RED to BASE then BLACK to EMITTER and COLLECTOR.

Give or take, on the RCA:
BASE to EMITTER: .08
BASE to COLLECTOR: .440

Give or take on the top row:
BASE to EMITTER: .005
BASE to COLLECTOR: .445

Are those expected readings for these transistors?

 

[laatsch55]

Gary, we want to check continuity to ground. Black lead at the star ground point, red lead on each transistor case. In resistance mode, see what we got there...

 

[jbeckva]

just checking in real quick. Gary the readings I was thinking were going to be done before the transistors were remounted... reading's MIGHT be good

Lee ya got the ball man... "work" has called and it was MAJOR... (eyeballs Joe ... SAN issues again, Mr Joe.. heheh)

 

[laatsch55]

Youlre tagged out bud, thanks for the set of fresh eyes!!