Resurrected a Customized WOPL 400

[laatsch55]

Now that's funny Scott....

 

[scottonnob]

Okay, a million things that demanded my attention for the last six months are now out of the way. So I went out to FINALLY bring up the first row of transistors on my WOPL 400. However, I started from the beginning of the process, so as to re-check everything before I put any fire to the unit. Unfortunately, the left backplane board is showing resistance. I shut everything down and knew to ask you guys what I should do next.

 

[jbeckva]

Where is your black lead? On the GND test point? What is that resistor above your hand with the alligator clip on the Output test point doing?

If it is measuring open from the black/ground test point to ground on the RIGHT (which would be a problem), then the right backplane would be missing a ground...

 

[scottonnob]

The black lead is on the GND test point. The red lead to the meter is contacting the transistor on the board. The resistor is just there for the purpose of connecting between the output and ground test point when I finally put power to the unit. I just soldered the resistor onto a couple clips for easy attachment when I move on to the next step. Only one clip is connected, the one on the output test point. The other is hanging free (I, just now, completely removed them from the unit and nothing changed in the readings). UPDATE: I just went out and took another reading, after doing what the paper actually says to do, "Remove the one wire to the upper left backplane 6-32 screw by removing the securing nut and floating this wire in the air," and the resistance disappeared. Duh! So, am I correct in assuming it's okay to move on with the procedure now?

 

[jbeckva]

The black lead is on the GND test point. The red lead to the meter is contacting the transistor on the board. The resistor is just there for the purpose of connecting between the output and ground test point when I finally put power to the unit. I just soldered the resistor onto a couple clips for easy attachment when I move on to the next step. Only one clip is connected, the one on the output test point. The other is hanging free (I, just now, completely removed them from the unit and nothing changed in the readings). UPDATE: I just went out and took another reading, after doing what the paper actually says to do, "Remove the one wire to the upper left backplane 6-32 screw by removing the securing nut and floating this wire in the air," and the resistance disappeared. Duh! So, am I correct in assuming it's okay to move on with the procedure now?

That solves the left "short" indication sure, as your connection to the bias transistor's metal strap should also be grounded to the chassis. However - with that wire on the left from cap ground to the left upper standoff still connected, you should have also seen the same short/low ohm reading on the right channel's GND test point as well as the left's. I see you have the two wires for GND1/GND2 ran between them, so one ground on one channel should short out to the same ground on the other's GND test point. Hook the chassis lead back up and remeasure between the right channel's GND test point and the right channel's bias transistor case/strap. If that still reads open, then you'll need to walk it back to the right channel's ground wires (the two whites between the backplanes), through the left and over to the left's ground inputs which should be fed by the main cap/star ground.

(Hard to explain without a picture, so let me know if you need one.. )

 

[scottonnob]

Yeah, I get exactly what you're talking about. I'll go out and re-attach the ground wire that connects to the lug on the left board and re-test. Thanks a lot for helping me out here.

 

[scottonnob]

Okay, I think I solved the problem and mystery. I reconnected the white ground wire, then probed all over the two boards between ground points, and all of them showed that they were connected. But when I probed between the ground test point and the transistor — nothing! So I took a look and the transistor and clamp on the right side and just couldn't figure it out. Then it occurred to me, I had the chassis powder-coated. So I took the clamp screw out and ran a very small file around the clamp screw hole, from the chassis side, reinstalled the screw and nut and, Bingo! The screw wasn't making contact with the chassis because of the powder-coating. But filing the hole out and exposing bare metal made the connection. So now, with the ground wire disconnected, I have open circuits on both boards between the ground test point and the transistor clamp. So, I should be ready to proceed, correct?

 

[jbeckva]

Sure.. biggest thing is that the outputs aren't kissing the chassis and shorting out. Give it a shot.

 

[jbeckva]

One row of the drivers on the bottom and one above it, that is. Check the cases to the chassis - should be open. Repeat the resistance measurement after each row and after draining caps.

 

[scottonnob]

Okay, now I got me a problem. I was just tightening the transistor screws, just to make sure they were snug, and I heard a pop when I just touched the last one. I knew what it was, but not why. So I pulled the board loose to take a look. As the photos show, one of the screw sockets pulled away from the board. And trust me, I come from a mechanical/machinist background. I NEVER over-tighten fastners. In fact, on something like this, that doesn't move or receive vibration, I only go light, finger-tight. Plus, the spacer, as you can see, is in place, such that the whole thing doesn't make sense to me. I checked the threads in the socket and they're fine. So it didn't bind and twist it off. Obviously this is only a support socket for the transistor. It doesn't carry current (right?). So I'm guessing that I can just glue the thing back in place and put it back together.? If so, what sort of adhesive should I use? Hot glue? JB Weld? Polyrazmataz?

 

[scottonnob]

Also, could you be more specific? Your instructions as to which transistors to install for the first bring-up confused me a bit. Is it one horizontal row, or one vertical row? Thanks.

 

[jbeckva]

Okay, now I got me a problem. I was just tightening the transistor screws, just to make sure they were snug, and I heard a pop when I just touched the last one. I knew what it was, but not why. So I pulled the board loose to take a look. As the photos show, one of the screw sockets pulled away from the board. And trust me, I come from a mechanical/machinist background. I NEVER over-tighten fastners. In fact, on something like this, that doesn't move or receive vibration, I only go light, finger-tight. Plus, the spacer, as you can see, is in place, such that the whole thing doesn't make sense to me. I checked the threads in the socket and they're fine. So it didn't bind and twist it off. Obviously this is only a support socket for the transistor. It doesn't carry current (right?). So I'm guessing that I can just glue the thing back in place and put it back together.? If so, what sort of adhesive should I use? Hot glue? JB Weld? Polyrazmataz?

Actually yes, those do carry the collector current which is the metal case of each transistor. You'll need to get that back on there with full integrity and conductivity, with a new one I would recommend.

Rows are horizontal across the width of the amp. What I was saying is you'll need to populate the first row across the bottom of the amp, plus one more - the bottom rows are used as the voltage amps/drivers for the other three rows which are what carry the current.

 

[scottonnob]

I guess I should consult Joe? I guess I'll leave it for today. No sense rushing. But thanks for letting me know that there is a conductivity function to the socket. But it appears that the conductivity is generated by the body of the socket contacting the metal ring within the mount. Where the socket pulled away appears to be only a base for adhesion. So as long as that socket is in there, properly aligned, the conductivity should be restored — right? It looks as though the only direct connection compromised by the break was where the pads meet, on the socket and board, which are not conductive. Does that sound accurate? However, regarding conductivity, where on the board would I check to make certain the socket has made the necessary contact? — One probe on the socket itself, but where would the other one go on the board to check continuity?

 

[jbeckva]

The other one across the same transistor. Both provide a path for the collector. You might be able to get away with one, it being in the driver position but yeah the via appears to have been yanked from the board. Should also feed the base connections for the other transistors in the vertical column it is in. Check that with a meter.

 

[scottonnob]

I checked all of them for continuity between each other and everything's fine. I just pushed the socket in with my finger, and all of everything on the board and the sockets checks out. I just need to re-adhere the torn socket back to the board and everything should be fine. It's just a matter of what adhesive to use. It looks as though they use some sort of epoxy when they build the boards. I'm guessing that any sort of adhesive that requires mixing two chemicals will do. JB Weld is the most common, but I also have other epoxy types that I've used on plastics before. Both surfaces are plastic. The adherence is between two non-metallic faces. There's no metal involved, so epoxy should be the best. I'm wait until tomorrow, when I'm fresh. Thanks for the help.

 

[laatsch55]

Scott, there's a lot of evidence of cold solder joints. Where they appear to "blob" up there has not been enough heat to get the solder to flow. Pic #3 shows the inside of the hole where the standoff has pulled out and there appears to be no solder on the inside of the hole. Properly soldered I have only pulled one out and that was in an EXTREME situation. Not enough heat on any joints in the pic that are tied to the power or ground planes...

 

[laatsch55]

Also, those leads need to be trimmed below the level of the standoffs and any solder on the face of the standoffs filed back to flat.

 

[laatsch55]

Okay, now I got me a problem. I was just tightening the transistor screws, just to make sure they were snug, and I heard a pop when I just touched the last one. I knew what it was, but not why. So I pulled the board loose to take a look. As the photos show, one of the screw sockets pulled away from the board. And trust me, I come from a mechanical/machinist background. I NEVER over-tighten fastners. In fact, on something like this, that doesn't move or receive vibration, I only go light, finger-tight. Plus, the spacer, as you can see, is in place, such that the whole thing doesn't make sense to me. I checked the threads in the socket and they're fine. So it didn't bind and twist it off. Obviously this is only a support socket for the transistor. It doesn't carry current (right?). So I'm guessing that I can just glue the thing back in place and put it back together.? If so, what sort of adhesive should I use? Hot glue? JB Weld? Polyrazmataz?


View attachment 31191 View attachment 31192 View attachment 31193 View attachment 31194

Resolder the pulled out standoff back in the hole. Twist or turn the standoff after you have liquified the solder again to get solder in the hole...

 

[scottonnob]

Okay, well, I've figured the whole mess out. The socket pulled loose, even with only finger-tight screws because the board wasn't perfectly flat against the spacers. The reason, and now that I've checked, it's the same on the other board, is that neither board is right. This is an old, four sink amp. It's one of the first groups to have come off the line. Unfortunately, and I ran into this elsewhere, if you recall, the dimensions of the chassis are, apparently, just a bit off from later runs. I had to re-drill two holes a long time ago for this reason. Anyway, the screw that holds the transistor and board doesn't line up. When the top screw is in place and has a nut on it, the bottom hole is at least an 1/8" too low to line up with the screw hole in the chassis and heat sink. I wasn't able to see this because the transistor and clamp, which were soldered in long before the boards were installed, blocked my view. So when the nut on the bottom screw was put on top of the board, everything canted and the board never got all the way down to the spacers. Therefore, when I put the screw in, there was at least a 1/16" gap between the board and the spacer, which was enough room to put pressure on the socket and pull it away when the board couldn't bend enough to contact the spacer. Christ, I don't know exactly how to remedy this problem. It isn't realistic to re-drill both the heat sink and the chassis. The misalignment isn't sufficient to allow a new hole to be drilled, and the present hole is too small to allow reaming it out enough. The only solution I can see is to use a Dremel to elongate the holes in the boards. Either way, it seems like I'm going to need to de-solder the boards from the connecting wires so I can remove both completely away from the rest of the unit. Otherwise, there is so much to fix, there's just no way to do it all with the boards still attached to the wires. The only other thing I can possibly think of is to just drill much bigger holes into the heat sink and chassis big enough to allow alignment, and then use a small fender washer on the outside of the chassis. I'd probably have to go 3/16" to get enough room, but at least it's on the back. Any thoughts would be greatly appreciated.

 

[laatsch55]

Yep, Dremel time...