WB Calipers M800

[greenmeanh1]

Diagram (corrected twice now)

[greenmeanh1]

Checked the AC ripple and there is none. Scope shows a nice clean DC signal on all four amp boards. Other than the positive on the left side shows +44v instead of +66 and we know the upper amp board on the bad side worked. I did the same test again on the bad side and just grounded the negative speaker to the chassis and the amp worked and has half power on the bad side. so i think i can rule the 55v and 66v power supplies.
As far as the power transistors, they seem to test the same on all the amps boards. Im going to do it one more time to be totally sure. Now,, not knowing how to even roughly test them i just probed the hell out of them in as mamy different probe configurations i could do. In a way they sort of seem to test like diodes. Example

Start with the 2922 transistors. Meter on Continuity (beep) Power off condition.
Red VOM probe to +55v (center pins of transistors)= 1,0,1 and 1,0,1 on all amp boards. now reverse leads.
Black VOM probe to +55 (center pins of transistors)= 540,0,540 and 540,0,540 on all amp boards.

Moving to the 1216 transistors. Meter on continuity (beep) Power off condition.
Black VOM probe to -55v (center pins of transistors)=1,0,1 and 1,0,1 on all amp boards, now reverse leads again.
Red VOM probe to -55v (center pins of transistors)=560,0,560 and 560,0,560 on all amp boards.
Take a coffee break lLOL

[greenmeanh1]

I meant to ask if those tests i just did tell anything at all about the transistor health or if there is a better way of doing it. I could pull them and test them on my multi function tester but its a pile of work and it would be great if my testing method meant something good!! Please let me know!!
Aside from that, thanks for all the commentary and suggestions,. I appreciate it very much. Hopefully by the time this thread is done it can someday come in handy for someone else who has one of these things.

[g1]

So far so good. When you say 'all amp boards' I hope you are checking the good channel also, as this is a good comparison.
Sounds like all your measurements had one probe on center pin. Now try between outer 2 legs on each power transistor, then with leads reversed also on outer 2 legs.

[greenmeanh1]

OK good call. I did that test as you mentioned above on the outer legs of the transistors. I get the same readings on all four amp boards. They all measure about 275 across the two outer legs and the same again when probes reversed. And yes i tested both channels for all of these tests thus far.

[greenmeanh1]

Found the problem, One 33k resistor open on the suspect amp board. So fixed it and bench tested it for hours so i was pretty happy but when i tried to put it all back together something happened (dont know what) with all my fiddling and it stopped working again so now a new problem,
Now on the upper amp board i have -26v showing up on all the transistors terminals. Its not from the amp supplies as best i can tell because its still there when i pull the 55v+- fuses so i think its from the speaker protection circuit which now wont turn on the relay either. I was so close now back in the sewer!! Thing is with the power off all the transistors seem to check out until i turn on the power then the upper amp board has the -26v thing.
question. Can i bypass the speaker protect circuit?? Involves lifting the two sensor wires to each of the transistor pairs and a third wire to the amp output and then bypassing the relay direct to the speaker.
Trying to think back to what i may have done and the only thing was, i had to de solder the wire from the amp out to the relay to make room to work and then resoldered the wire to the relay. Interestingly that SP relay circuit runs off 26v+-. Leaking back to the transistors is where im thinking.

[g1]

I guess you are sure you connected it back up to the exact same spot?
I don't see where bypassing the protect will get you? You could do it to check for DC at the amp output, but be sure you do not have a load or speaker connected.
I'd suggest you get the datasheet for the relay and draw out the circuit. Then compare how it's wired on the good and bad channels of the amp to make sure it's right.

[greenmeanh1]

I have 26 volts at the speaker out. Ruled out the speaker relay after bypassing. It was doing its job and was not leaking anything back to the transistors. So, with the 55v transistor supply pulled, and the 26v sp protect pulled, the only thing left is the 66v power supply that powers the pre stage on the amp board so a full check of diodes and caps is in order. With the power off the power transistors still seem to check out so hopefully its not that. I cant help but wonder if the one leg of the 66v supply that was only showing 44v had anything to do with it. I should also point out that the -23volts is only showing up on outputs of the upper amp board. The lower amp board with the initial problem seems fine. Both amp boards are fed by the same 66volt supply. It gotta be a cap or diode on that upper amp board.

[greenmeanh1]

Disconnected the +-66v supply from both amp boards and the -23 volts disappears off the transistors and the sp relay click on. Still have -66 and +49 instead of 44v now straight out of the supply unloaded. So, then i tried hooking up the lower board 66v supply and see if the relay clicks on. it does. So, now i guess ive narrowed it to the upper amp board leaking somewhere. Just a quick glance and there appear to be 4 33uf 100v caps, two off the transistors and two on the power supply side that could be likely culprits.

[greenmeanh1]

A few updates. I worked my way through the upper failed amp board and tried to prove it to the schematic dmeek had posted way earlier in this thread. Fairly time consuming process for a beginner. Good news is the schematic is bang on for the most part and i have confirmed most if not all the parts. I uncovered some small errors in the schematic i will note and seek some advice on. Most all the parts tested well with an ohmmeter and a few resistors were out of tolerance.
Still haven't got around to changing out the four 33/100 caps cause i don't have any in stock. I am hoping that is where my problem is.
I added a pic of the updated parts on the schematic with a few notes. In the red circles are part values populating my amp boards that are different from the original drawing.. There is some question how one of the 33/100 caps is drawn in the red square, top left.. In the other red square is a 10 ohm that does not appear on my board although it could be mounted on the solder side.
Second pic is the amp board with all the parts/ readings, labelled thus far and seems to trace out to match the schematic. In red squares shows the main parts that differ from original schematic. Zenier is marked in a blue box.
So, if anyone can give a clue on how -26v is getting to the power transistors somehow from the V2 supply (V1 disconnected) i would be quite interested.
Update: Found the missing 10 ohm,, it was on the solder side.

[greenmeanh1]

I have added an updated drawing of the amp board schematic. I think i have it correct. If anything doesn't look right please let me know!! I have edited the drawing a few times now!! Im sure it wont be the last edit LOL.

[greenmeanh1]

Yet another long winded post.
Geez, I went to my local electronics spot in Toronto and they don't have 33uf 100v caps. They have them on order but could take a while. Same with any online orders, its just waiting. So, i got one more place i can try locally tomorrow and if it dont work out i guess its digikey fast and expensive or china slow and crappy. On top of that my china solder sucker thing s993a just cooked the element so i had to order one of those tips from Romania as it was the only place i could find the part. I had turned up the thermostat on the thing a little and i guess i burnt it out as a result. So, a bad couple days since i had it fixed this amp with a 33k resistor and then broke it again, trying to reassemble.. Sorta looking at the amp and what might have happened, when i lifted the amp out wire from the relay to make room to work its possible the wire could have made contact with one of the rails of 8 power supply caps which had not been discharged. Only thing i can think of. Don't know if or what that might do but i think that is one possibility in reviewing my movements. The other thing that happened is i broke the line input wire off the amp board when i was fiddling around making room. Didn't notice till the amp was back together and powered up and failed. Found the wire later after i took it apart again.
Amp is a pain to work on. All the wires are too short and everything is soldered in place. I'm seriously considering putting some pins/plugs drilled out and soldered on the amp boards and adding longer wires so everything folds out on the bench instead of the struggle i am having with these super short wires.. Amp just wasn't built to be serviced easily. The other thing im going to do is mount a piano hinge the bottom rail of the heat sinks which make up the sides of the amp and hold the two amp boards so you can just fold them down to splay out the amp for service and display. So my big question:
The 55v+- to the boards are pretty beefy wires and huge solder joints on the boards. I imagine they will be carrying some current and i wondering what sort of wire connectors would be best for these?? I was thinking of using spades like on a speaker terminal. Thoughts??
Final question. There is a ton of flux on the amp boards and it looks like crap. I want to remove it. I have flux cleaner spray. Wondering if i just spray the stuff on or should i attempt to scrape the boards first with a wire brush or something??
Thank you for your indulgence. Im probably driving the guru's nuts.

[Enzo]

No 33uf 100v? try 39uf or 47uf. it is just a filter cap on a power supply line.

[g1]

Remove whatever flux you can easily first while it's hard. The flux cleaner will soften it and it will still need to be removed, so get rid of the excess first for less mopping up.
With the spade lugs it may not be easy to mount them on the board. I'd try using the existing wires and adding some in-line connectors, I think you can even get spade lugs like that.

[twitch1519]

Hey greenmeanh1 I'm in possession of an WB M500 which seem very simmilar. I have gone through this entire thread for info as needed due to NO info on these being available as you know, (besides this thread) lol THANK YOU. Anyways, i have a few questions for you about some of the components inside and wondered if you could find a few mins to help out? Thanks again!