Broken eBay 700B - Now what?

[laatsch55]

Doug, it really doesn't look that bad.....

 

[Northwinds]

View attachment 16547

Nice!

 

[gadget73]

Nice. Looks like one new main filter cap and one original? Gotta love minimalist repairs.


Dunno, things like that bug me. It looks bad visually, and I can't help but think that if one part died, the one right next to it can't be a whole lot better. Mismatched outputs per channel is something else that irks me. It might work, but it just feels wrong. I'm too picky sometimes though.

 

[fitz43]

I'm looking at the schematics for this thing (PL20B) and have a question. On the physical location drawing 402453 Top left quadrant of the drawing it shows Q3 with the number 34 inside a circle. Q4 with the number 35 + 61 inside circles beside it. R9 with the number 7 inside a circle.

What do the numbers inside the circles refer to? A parts list? I have a couple of parts list sheets but the parts aren't numbered on it.
Thanks.

 

[laatsch55]

Pic??

 

[fitz43]

View attachment 17896

 

[laatsch55]

Doug...look on the schematic...they either correlate with a jct or wire I believe.

 

[fitz43]

Here's the area on the schematic.

 

[laatsch55]

That don't tell us shot does it?

 

[fitz43]

I've looked at it more than a few times trying to make sense of it. So far, I haven't figured it out.

 

[gadget73]

I was also going to guess that it would match up with the schematic somehow. You'd often see things like that on Sams schematics with voltage readings or whatever. Maybe the board layout drawing was supposed to go with a marked up schematic, and it just never got paired up ?

 

[laatsch55]

That was my thinking to, layout designations that got put on the component layout..

 

[Gepetto]

I've looked at it more than a few times trying to make sense of it. So far, I haven't figured it out.

Most likely there is a BOM (Bill of Material) associated with this board and this is the item number on the BOM.

 

[fitz43]

That was my thinking to, layout designations that got put on the component layout..

Wouldn't each device have two numbers depending on what channel on the board it was?

 

[fitz43]

I've been trying to follow the recent posts about the star grounding, and have a couple of questions.

Stock backplane and PL20B driver board.

The 2- #16 grounds going to the -(minus) speaker outs. - is the stock routing followed for these wires if I replace them?(along the bottom)

"The RCA input ground plane should be isolated from everything. There should only be shielded cable grounds and shield on that anymore."

OK, what do you recommend for replacement pieces for the RCA inputs?

"Did you cut the bare wire tying the RCA input ground plane to the minus speaker posts?"

Will do.

"The single #20 wire tying the old driver board ground to the 3 tab terminal strip on the back wall should also be gone by now..."
By "gone" do you mean now tied to the BABB? What about the other lead which goes from the minus speaker posts to pin 6R of the driver board?
That needs to go to the BABB as well?

 

[laatsch55]

Doug, are you saying you have Joe's driver board? The stuff you quote is with the WO driver board...

 

[fitz43]

Doug, are you saying you have Joe's driver board? The stuff you quote is with the WO driver board...

Not in this one. This one is stock backplane and driver board.

Can the grounding system be configured to include the star grounding topology or do I just leave it all as the factory designed and assembled it?

 

[laatsch55]

Yes it can be converted to the grounding scheme yes. For the stock version, take the white ground wire from the board to the BABB. Cut the wire between the ground plane and the speaker neg posts. And isolate the RCA input plane...

 

[gadget73]

Not to hijack too much here, but does that also apply to amps with a stock PL36 driver board ? What does the change to the grounding scheme get you anyway, reduced noise levels ?

 

[fitz43]

I found some time to do some fabrication and trying out Nav's wire. I need to buy some sharper strippers!