WB Calipers M800

[greenmeanh1]

Any one heard of these power amps? Thing is a monster. Its suffering the same fate as a lot of power amps around here with a channel out. Its next on the list of amps to try and fix. Can't locate a schematic anywhere. Seems well put together for an 80s era amp. Sixteen caps in two parralel rails on the power supply. Looks like it was hand built. I suspect the power transistors which are Sanken 2sa1216's and 2sc2922's LOL.
Haven't pulled it apart yet. Here we go again!!
Couple of pics

[Jazz P Bass]

Wow.

What a tank.

[dmeek]

I saw an M300 several years ago. I drew the power amp board schematic.
Not guaranteed 100% accurate of course. Maybe some help.

Doug


http://music-electronics-forum.com/a...1&d=1451255730

[greenmeanh1]

Thank you Doug..I appreciate that drawing. Appears to be quite similar to the amp boards in the M800 which has four amp boards,, two on each side. Wont know till i pull them for a closer look. Same output transistors i see.

[greenmeanh1]

Hey guys, Been a while. Like a whole year. last time i was spending time on this forum my GS3000 console went down which side tracked all other repair projects. Finally got that fixed and then summer was all renovations on the rear of my studio. So now that its cold i'm back to my list of winter gear repair projects. Last year i fixed a bunch of stuff thanks to the help of guys on this forum.
Marshall Valvestate combo
Fender Power Chorus Combo
Fender Blues Deville combo
Peavey Encore combo - just did this one last week
Two- Johnson Millenium 150 combos
Two- Fender Concert combos
Randall RG80 restoration
Biamp 400w power amp
Tascam 106 mixer
SGX2000 guitar processor-- broken again
Lexicon MP1 FX processor-- broken again
A&H GS3000 mixer- Took a while to figure this out.
So this winter i am going to try and knock off the rest of the pile to include
WB Calipers M800 power amp- topic of this thread
Two 900watt Carvin power amp restorations
Mitsubishi 300w A5361 Power amp
Two Tascam DA30 dat recorders- both with tape loading issues
Soundscape SSHDR1 plus recorder- power supply issues
Im sure other stuff will come up as it always does.

Anyway got that spiel out of the way, back to the WB Calipers M-800. Normally an amp like this would be a complete nightmare for me but fortunately one side still works so i can use the working side to fix the bad side hopefully.
The problem i have right now is the amp is not so easy to take apart. Instead of tapped holes there are nuts and washers everywhere and most cant be reached without a special wrench. The frame is riveted together as well.
So already planning some accessibility upgrades for future servicing of this amp. So, im going to drill out and tap all the bolt holes and do away with most of the nuts and washers holding the side heat sinks on. The amp boards are attached to those heat sinks. There are 16 nuts on each side, of which most are unreachable. Once i get the sides off which will take several hours i will be able to look around and do some tests on the boards. Pics coming!!
I added a short video as well
https://www.youtube.com/watch?v=K4Byj6F0cNo

[greenmeanh1]

Couple more vids of taking it apart.
https://www.youtube.com/watch?v=pq_3-c2NN6c
https://www.youtube.com/watch?v=1F0Kyjp6Be0
So everything seems to check out in the power supply I got 55volts +/- going to all the amp boards. If the transistors were shorted i imagine the speaker protection circuit relays would not switch to on and they do. I can hear a very small amount of signal coming from the bad channel almost like the output is shorted. Looking a little further it appears the relay for the speaker protection circuit may have a short in it. Next step is to bypass the relay. Im feeling pretty confident im on the right track.
Video part 4 https://www.youtube.com/watch?v=aQ3TI4o6wXA

[greenmeanh1]

Well, nix on the relay . It was fine, so back to checking out the amp boards.
I have no idea how to check transistors in circuit with the amp on but i noticed i have around 57 DCvolts +/- going to all the center pins of 1216 and the 2922 transistors. No other voltages on the other pins on the same meter setting.
With amp powered on and no input i get about 25mv off the good speaker out and about 39mv off the bad speaker out regardless where the master volume is set. Not sure what that means if anything.
As i mentioned before i get a very very small amount of signal off the bad side. I had been doing the thumb on the end of a patch cord as a test and i did notice that if i had any static in my body when i touched the end of the jack i would hear a loud pop through the speaker. not sure what that means either. With no schematic not really sure where to go next. Probably time to pull the good side apart so i can access it for comparison tests. Appreciate any thoughts.

[greenmeanh1]

I made a drawing of one the four amp boards that i will post. Not complete LOL but its where im at thus far. I pulled the good side apart as well so i can start testing between the two. The one thing i did notice is the bad side amp boards have a lower voltage on the blue +66v supply (shows +44v) and -66v on the orange,, whereas the good side shows +66 on both blue and -66 orange. So im guessing perhaps maybe the +66v supply is being pulled down or the B2+PS is bad. Good place to look??
The main supply and the 16 6800uf caps (eight on each channel)all check out and provide a solid 55v to all the amp boards and the center pins of the power transistors on both sides of the amp. I have about 30mv at the speaker terminals on both channels. What is this voltage??and does that tell me the transistors are OK?? when amp powers up the speaker protect circuit clicks on showing no faults.

[g1]

There are independent power supplies for the 2 sides? (+66V rail is not common to both amps)
Does it use connectors or is everything hardwired? How hard is it to swap 'modules' from one side to the other?

[greenmeanh1]

Everything is hardwired. The amp is split into 2 separate sections with separate PS's for each side. The only common thing might be the big power transformer but everything after that is like two separate mono amps in one box.
There are numerous PS's but i will start with the main ones.
So, starts with the common power transformer, which feeds two rectifiers (one left Ch, one right Ch. This feed two banks of 6800uf caps (eight on each channel) this provides two 55v+, ground, 55v-feeds, one feed for each channel. Those feeds go directly to the amp boards of which there are two amp boards on each channel. Each amp board has two pairs of Power transistors for a total of 8 on each channel. It appears one amp board provides the speaker negative and the other amp board provides speaker positive.
Then there is a second set of power supply's (again one for each side) which feed 66v+, ground, 66v- to the amp boards. The bad side of the amp is only getting 44v+ instead of 66v+. The good side gets 66v+ and 66v-. Couple of pics added of the amp boards.

[g1]

Doug's schem.(post #3) shows a +V2 and -V2 near the upper left and right side of his drawing. Could your +/-66 be going to similar?

[greenmeanh1]

The schematic seems quite similar and yes V2+ is the +66v supply or in my case is showing 44v on the bad side. I added a couple more vids for a total of 7 vids on this topic now.
#5 https://www.youtube.com/watch?v=qfS_55fCnsw
#6 https://www.youtube.com/watch?v=-pcmVE68gac
#7 https://www.youtube.com/watch?v=7zJsfAAQuQU

[greenmeanh1]

Trying to pick my way through that schematic dmeek posted. Im not very good at this stuff but i am trying to verify the schematic one part at a time. Output stage seems to map out as per the drawing.So,,
55v- is getting to the center pins of the 1216's
55+ is getting to the center pins of the 2922's
All .33 ohm resistors to the right side pins of power transistors check out
All 10 ohm resistors to the left side pins of transistors check out
The two diodes between the power rails check out.
That is as far as i have got on the output side. I will sketch out some more tonight.
On the input side i dont think the schematic is the same. I have a 1.2k on the input but the parts that follow on in the circuit seem different. I also lifted the +66 v line off the amp boards. That got the supply volts up from 44v to 52v when lifting the wire on one of the boards.
A question. Would the 66v supply be considered a power supply for a differential amp circuit?? Trying to learn something LOL

[greenmeanh1]

OK something happened and i cant explain it. So, i was doing a few tests with my scope (old Tektronics 456) At one point i put the probes on the speaker and all of a sudden the amp starts working and there is signal making it from the amp input to the speaker. Of course as soon as i removed the test probes from the speaker it stopped working again. WTH!! So i tried it a few more times and same result. So. i also found when removing the positive scope probe from the speaker, the amp still worked.
I have no idea what is going on here.

[greenmeanh1]

I was thinking because the amp has two amp boards on each side (one for positive and one for negative) perhaps the board that provides signal the ground side of the speaker is not functioning so the scope was acting as a ground to the good working amp board that provides the positive speaker feed. Its the only thing i can think of.
Stumped