Inverted back plates build

[NavLinear]

A quick question. What voltage rating, value and age are the Panasonic reservoir capacitors in your amp?

The power supply of this amp is pretty simple so taking a couple of measurements can eliminate most failure areas. If only one channel is dicked up than the DC power source may not be your problem. But to cover all bases another sanity check here would be to measure rail voltage with your meter (DC setting) and to look at both outputs with your oscilloscope while under load.

 

[grapplesaw]

A quick question. What voltage rating, value and age are the Panasonic reservoir capacitors in your amp?

The power supply of this amp is pretty simple so taking a couple of measurements can eliminate most failure areas. If only one channel is dicked up than the DC power source may not be your problem. But to cover all bases another sanity check here would be to measure rail voltage with your meter (DC setting) and to look at both outputs with your oscilloscope while under load.

Thanks Dennis.
The panasonics are 100 volt 18,000uf. I used these in my last build with success and had run them through the condtioning cycle. I have conditioned one of your caps at 150 volts and have the other on right now. So I will swap out the pano's.

Both channels were the same distortion when tested individualy.

I will check on the ic being in backwards, had crossed my mind but would not believe possible right,

I will also break the ground to the chassis for testing.

I will work on the two channel shop of both ic in and out.

Thanks again
Glen

 

[laatsch55]

The process of negative feedback will introduce problems downstream of the IC to be introduced to the IC, IIRC where the feedback is introduced back into the V/A stage. Joe told me once but I've forgotten. So....even if you are seeing a clean signal at the input and a distorted signal at the out put does not mean the distortion is from the IC, It could be from any component downstream of the IC but affecting the iC due to negative feedback. With the distortion showing on the minus side of the sinewave I'm leaning towards something besides the OPA op-amp.....

 

[laatsch55]

But it certainly won't hurt to swap them out and see. But what are the chances that both IC's are bad in the same way?? Now, with that being said, they probably will.......



On the other hand, I have seen that kind of sinewave when a bad output insulator was allowing a LITTLE communication with the chassis. A solder splash or whisker can also cause that type of oscillation. When the sinewave breaks up like that it can be called an oscillation...

 

[grapplesaw]

But it certainly won't hurt to swap them out and see. But what are the chances that both IC's are bad in the same way?? Now, with that being said, they probably will.......



On the other hand, I have seen that kind of sinewave when a bad output insulator was allowing a LITTLE communication with the chassis. A solder splash or whisker can also cause that type of oscillation. When the sinewave breaks up like that it can be called an oscillation...

I think you have it but will go down the road I am on. It's very easy the swap control boards so will do that first if still a problem. I pulled off in chassis ground just for that reason to see if one leg of driver to close to chassis.

I was going to start pulling out drivers one row at a time. i have replacement board built now.. IC were in correctly and dought they are problem I think there is a piece of shit behind the back plates so will get compressor and give a good blow,yippie, at some point. Capacitors conditioned and changed out, I know Dennis realy wanted to see them in there anyway

 

[laatsch55]

Yerp, 100 volters are a gamble.....

 

[grapplesaw]

Well no improvement with new caps and the ground removed from chassis.

The honey do list must now be looked at. Will change out control board later today.

 

[grapplesaw]

Update!!!!

Well it is F#ck!!

New board same thing!

Checked all drives with ohm meter all good so will pull and check them with trans tester

Checked Diodes on backplate all seam ok as they passed ohm meter only one way.

Other than that are there any other components that can be installed wrong way?

I pulled the B - driver and pre driver in row 1 and 6 of both channels and had a look
No sign of any junk or lack of clearance.

Although I ruled out the bridge rectifier due to turning off Ac did not stop distortion could one of the snubber caps on it cause any anomaly?

It's in the backplates then.

Will build a new pair and install thoughs guess

I put Joe's connect kit on the new control board as I was expecting to remove it again, I still like to solder connect the board.

 

[grapplesaw]

So here are some shots of the back plates
Any ideas on what to check in please before I pull them out

?

 

[laatsch55]

Glen, it could be so many things...just a process of elimination now...

 

[grapplesaw]

Glen, it could be so many things...just a process of elimination now...

I Hope it is a bit crap on the back plates. Thinking I am going to take out to the shop and blow it out one time. If no good results then I pull it down.

 

[laatsch55]

Not a bad idea....

 

[grapplesaw]

So I hauled to unit out to me shop and blew the loving hell out of it, not really, and tested it again no change

So I pulled the drivers and tested it with just the first two rows in and to my amazement no distortion

As I pulled each driver I inspected them and tested with my high and low setting on the B&k 502b tester. All came through as good. I also carefully looked at the insulated pads. I found one with what looked like a pencil line on it, not to heavy a line but noticeable, also some of the pads had slight tearing around the end of the driver but not alowing any contact as I tested them for ground fault before doing all this.

So I will install each row by row and test as I go. I will replace any suspect pads and not tighten as much this time.

Glen

 

[laatsch55]

AH!!! Progress....

 

[NavLinear]

Remember that the Sil-Pads are kinda like a condom - one time use only. If you have enough (Sil-Pads not condoms) I would suggest that you replace the ones were under the removed the drivers. It's better to be safe - don't want this one to bite you on the ass later.

The torque for the transistor hold down screws is a few inch pounds - can't seem to find the number at the moment so be careful of over torqueing the screws.

 

[MarkWComer]

Remember that the Sil-Pads are kinda like a condom - one time use only. If you have enough (Sil-Pads not condoms) I would suggest that you replace the ones were under the removed the drivers. It's better to be safe - don't want this one to bite you on the ass later.

The torque for the transistor hold down screws is a few inch pounds - can't seem to find the number at the moment so be careful of over torqueing the screws.

So- just snug enough to keep 'em in place... like a condom!

 

[NavLinear]

So- just snug enough to keep 'em in place... like a condom!

Five inch pounds Mark - not six or seven - just five. Is that enough????????

 

[Gepetto]

So I hauled to unit out to me shop and blew the loving hell out of it, not really, and tested it again no change

So I pulled the drivers and tested it with just the first two rows in and to my amazement no distortion

As I pulled each driver I inspected them and tested with my high and low setting on the B&k 502b tester. All came through as good. I also carefully looked at the insulated pads. I found one with what looked like a pencil line on it, not to heavy a line but noticeable, also some of the pads had slight tearing around the end of the driver but not alowing any contact as I tested them for ground fault before doing all this.

So I will install each row by row and test as I go. I will replace any suspect pads and not tighten as much this time.

Glen

Are you using the 0.009" thick Bergquist SIL-PAD 400 insulators Glen?

I have repaired several amps that were built using the green colored, very rubbery insulators. Those tended to pierce through without much coaxing. All the edges around the screw ends of the TO-3s had pierced the insulator in the shape of the transistor end.

 

[grapplesaw]

[ have risen to the occasion! New rubbers and light pressure. It was a nice ride till I got to the 5 th row. Re and re with different trans and still distrortion. I released all the screws in that row and distortion cleared. I then tighten left bank and still good . Then right cannel and low and behold it was back. Switched one more time these two and no change. Release screws distortion gone. Removed fifth row and installed 6 th row. Same deal. So when tightening something is shorting. So I proceeded to heat all the wire connections at that end and raise wires a little. No improvement. I then re entered the thermal senser as it looked close to one edge of back plate. Still no good

So something is shorting in the right channel backplate
I know what you are thinking ::: you have not trimmed the soldered components short enough. Maybe but I don't think so. 50/50 at best

I am getting real good at putting the transistors and have the following set up. I put some shirk rap over the mag pencil as I was not realy waiting long between power cycles and the discharge unit did I not have long enough leads and I was pissed off and and
Anyway it doesn't matter, right Lee , have a look at the photo's

Any ideas before I plull the thing down to a shell?

ATTACH=CONFIG]22554[/ATTACH] I

 

[grapplesaw]

Are you using the 0.009" thick Bergquist SIL-PAD 400 insulators Glen?

I have repaired several amps that were built using the green colored, very rubbery insulators. Those tended to pierce through without much coaxing. All the edges around the screw ends of the TO-3s had pierced the insulator in the shape of the transistor end.

Well there you go

The answer is no! They say sil pad 400 .007

So they are to light right