WOPL 700 fuse and power transistor problems

[plex]

Hi everyone. One day in the past, I was playing my fully WOPL'D 700 series 2 at a moderately high volume, when one of the channel fuses blew. When I replaced it and turned it on again, it blew again.

We took it upstairs to open it and diagnose it, and the first thing we noticed was a loose output wire coming out of the driver board. We fixed it, and did a visual inspection, but the problem was still there-no power to the channel. We decided to take the power transistors out and redo the bringup process, but the light stopped dimming after the 5th row. We tried to redo this multiple times, and reseated the board and fins pretty well, but it still did not dim.

I have attached a few pictures of the 700 as it is now.

I just checked the voltages as well: +15 & -15V on the driver board check out, and rail voltage is about 106 V. The bias on the right side seems closer to normal at around 302mv, but the left side only has 68mv.

Also, there is only 0.7mv on the output of the right side, but 1.4mv on the left.

And several times that we have been working on the transistors, there has been sparks due to a loose connection between the transistorsand board. Can this damage the transistors?

Any help you can offer is greatly appreciated.

 

[J!m]

I don't know the answer, but those big gray resistors appear to not be fully soldered in to me...

 

[plex]

They are, however they are fully soldered. It just looks like they because the solder doesn't adhere to the pads very neatly.

 

[Pulpmillguy]

I take it you have gone thru all of the other steps in the bringing up procedure and no issues, all voltages seem to be OK (106 on the rails...nice!) so it has to be in the backplane.

You say the DBT stays bright when you put the last row of output drivers in...have you checked the transistors for shorts? Have you always put them back exactly where they came from?

Just dreading the day when something happens to mine (well, it already has but that was pre-WOPL...hope it never happens again)

Good luck!

 

[mlucitt]

It just looks like they because the solder doesn't adhere to the pads very neatly.

What type of solder are you using and what is the temperature or wattage of your soldering pencil?
Solder typically flows very well on the White Oak Audio PCBs, unless they have been contaminated with an oil-based cleaner.

 

[plex]

I'm using 60/40 solder and an iron with a max of 450 degrees Fahrenheit.

I took out the boards yesterday and decided to redo the bad joints. Still doing it now and they're starting to look better. Will post back when I put everything back and testing again.

 

[mlucitt]

Who made your 60/40 solder? Everyone has their favorite and you can start a flame war by saying one is better than another.
I am just curious.