BIG problems

Michael F

Michael F

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I just finished installing Dons output board, Dim Bulb test checked out, fire up the amp, relays engage after a few seconds, left channel was ok, right very distorted.
Swap the left and right speaker input to relay board and there is no longer output anywhere.
All B+ and B- 5amp fuses blown.
I followed instructions to the letter and proceeded with extreme caution.
WTF happened?
I tore all that stuff out and put everything back as it was and will replace the fuses first thing in the morning when I can buy some and see how it goes.

Totally bummed :sad2:
 
laatsch55

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Also, we should move this thread to the DIY section....you OK with that??
 
Michael F

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laatsch55 said:
Also, we should move this thread to the DIY section....you OK with that??
Click to expand...
Sorry for not posting in the right forum. Yes it`s the 700B, what kind of pictures would you need Lee?
There is nothing visually obvious ,to me anyways. Like I said, I could not have been more careful when installing the board, I checked, doubled checked every step and re checked when all was done, my soldering skills are excellent too, that's what really pisses me off..
 
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Michael,

If you're not bringing this thing up on a "dim bulb tester", you seriously need to build one before powering it up again. You will be going through some fuses and possibly blowing it up.

I had problems getting Don's DC board installed in my 700B as well. You can check that out in my thread "Zach's 700B thread" (or something similar.) Mine would draw massive power, that I suspect was due to oscillation, but never confirmed it. I believe that with the output zobel out of the circuit at power up (I think that's right) it would become unstable, and cleaning up the front end calmed this down so it could settle. Might be talking out my ass here, and would love to be corrected if that's way off base, BTW. I do not claim to be an expert.

Basically, I changed the amp's ground scheme to the one Gepetto recommends in the PLWO archive and added snubber caps on the bridge (see mlucit's (that's likely wrong spelling) schematic), and now it comes up just fine. I don't know which change fixed it, since I did both at the same time. Sorry.

Interestingly, mine has distortion in the right channel also, but I'd be shocked if it was related to the board. It's been almost 6 months since I had looked at it due to being busy with responsibility stuff and knee deep in functioning audio gear. Well, that and I'm pig headed. I'd like to figure this out on my own, but will be back to ask for more help soon if needed. Mine appears to be slewing as best I can tell. I'm not quite done with the tests from the PL manual on this. Need to swap outputs from left and right to see if it follows. Anyway, that's for my thread, not yours.

Zach
 
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Michael F

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OK, replaced 2 B+ and 2B- fuses, bulb bright and no display.
Remove both channel B+ and B- fuses, bulb dims and display lights up

Ch. 1 B+ fuse only, bulb dims
Ch. 1 B+ and B- fuses in, bulb bright
Ch. 1 B- fuse only, bulb dims

Ch. 2 B+ fuse only, bulb dims
Ch. 2 B+ plus B- fuses in, bulb bright
Ch. 2 B- fuse only, bulb gradually dims but there is lots of negative DC on the output.



This doesn't sound good at all...

DC protect board removed, everything put back to stock form btw.
 
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Gepetto

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Michael F said:
OK, replaced 2 B+ and 2B- fuses, bulb bright and no display.
Remove both channel B+ and B- fuses, bulb dims and display lights up

Ch. 1 B+ fuse only, bulb dims
Ch. 1 B+ and B- fuses in, bulb bright
Ch. 1 B- fuse only, bulb dims

Ch. 2 B+ fuse only, bulb dims
Ch. 2 B+ plus B- fuses in, bulb bright
Ch. 2 B- fuse only, bulb gradually dims but there is lots of negative DC on the output.



This doesn't sound good at all...

DC protect board removed, everything put back to stock form btw.
Click to expand...
what resistor value and type are you using in the Zoebel network that is present on Don's board? That is a critical component.
 
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Michael F said:
Resistor measures in at 6R but I cant make out the value of the cap, see pic.
Click to expand...
The resistor must be a metal oxide or metal film type. What instructions did you follow to install? Do you have a link?

BTW, I have posted the optimal ground wiring schematic for the PL700B on this forum in the WOPl Archives section
 
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Michael F said:
Here is the installation manual
Click to expand...
Step # 30 and #31 can be improved upon.

The white wire that you routed from the bus bar between the caps (star point ground) twisted with the 2 black AC wires in step #28 and #29 should be the one and ONLY wire to be connected to pin 6 of the terminal block. The White Wire from (pin 5 of) the control board should route back to the same star point ground ALONE and by itself.

There should be NO connection of the metal plate at the input jacks to the star point ground. Instead the ground braid from the shielded wires that run to the front pots should be connected to this plate (it probably already is done this way). The other end of the ground braid FROM the pots to the control board should be connected to the control board at pin #2 of each channel input (it probably already is done this way). You will find that the ground braids from the shielded cables are connected together at the pots and attached to one of the 3 pins of each pot.

This wiring will come closer to matching the instructions I provide in ground schematic. If in doubt send me a picture of what your input jack looks like.

Ground wiring is very critical inside the PL700 to attain maximum performance and much misunderstood. This picture provides some hints about how to properly wire this input plate.

DSCN0007.jpg
 
Michael F

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Gepetto said:
Send me an equivalent picture of your amp in this area.
Click to expand...
First off, thank you kindly for your input so far, you`ve no idea how much it`s appreciated.
Please note that the board has been removed. The wire that was terminated to the cap buss bar is still in place and tied in with the 2 negative speaker terminal, white wire going behind driver board and input jack shields.
At this point I`m more interested in getting the amp working without the protection relay rather that speculate what went wrong.I did everything except replacing the input jacks, they did not come with the kit.
My amps serial number is 474-1848 What is the correct schematic for it?
 

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Gepetto

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Michael F said:
First off, thank you kindly for your input so far, you`ve no idea how much it`s appreciated.
Please note that the board has been removed. The wire that was terminated to the cap buss bar is still in place and tied in with the 2 negative speaker terminal, white wire going behind driver board and input jack shields.
At this point I`m more interested in getting the amp working without the protection relay rather that speculate what went wrong.I did everything except replacing the input jacks, they did not come with the kit.
My amps serial number is 474-1848 What is the correct schematic for it?
Click to expand...
Can you carefully cut off some of the ty raps and separate the wires for the photograph so I can get an idea what is going on here.

Were the Zoebel components stock on your amp or did you change them? The reason I ask is that the 224 value on the 2 green caps is wrong. That should be 104 (0.1uF not 0.22uF)

The resistor value appears correct at 10 ohms in parallel.
 
Michael F

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Gepetto said:
Hi Mike
I also need a photo of the input jack area to help you out.
Click to expand...
Here you go, let me know if you need more. I did not change the cap or resistors btw.
 

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Hey Michael,

Going with that post you made earlier (major negative on the right channel??) and from the pics, look very carefully at that power buss wire to the far right on the channel strip of transistor sockets next to the speaker outputs. Although I can't say positively, it sure is very close to the transistor screw threads securing the right side of the transistors? Is it making any contact with the screw threads? Could it have when the DCP was installed?

Do you have a ohm meter? If you do, pop all 4 fuses, then measure across the 4 diodes that bridge across the center tabs of the chassis. If you have a dead short (less than 3 ohms)... you have problems. Also measure with one lead on the chassis itself (I normally use a screw hole with an alligator clip on it), the other across the collectors (should be the larger center contact on the back of the transistor sockets). That could be an indication of a mica insulator failure.
 
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