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Thread: WB Calipers M800

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    WB Calipers M800

    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 picsClick image for larger version. 

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    Supporting Member Jazz P Bass's Avatar
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    Wow.

    What a tank.

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    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
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    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.

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    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

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    Last edited by greenmeanh1; 12-17-2017 at 12:58 AM.

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    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

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    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.

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    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.
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  9. #9
    don't forget the joker g1's Avatar
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    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?

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    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.
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  11. #11
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    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?

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    Last edited by g1; 12-20-2017 at 07:23 PM.
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    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

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    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

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    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.

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    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

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    Get it back in that working condition with scope hooked up and see if the +66V line has changed. Then you will know if you are dealing with a single problem or multiple issues.
    Part of it may be that you are providing a ground connection for the speaker output via the scope.

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    you are providing a ground connection for the speaker output via the scope.
    That gets my vote.

    A simple test, ground your scope at the circuit rather than right at the speaker. If the speaker no longer sounds, the speaker has lost its ground connection somewhere.

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    you are providing a ground connection for the speaker output via the scope.
    That gets my vote.

    A simple test, ground your scope at the circuit rather than right at the speaker. If the speaker no longer sounds, the speaker has lost its ground connection somewhere.

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    Did that. I got the same readings as before. -66v on both the orange wires to both top and bottom amp boards but only +44 volts to the blue wires on both. Of course we know the good side of the amp has +-66v to the same top and bottom boards.
    I guess the next test i could do is disconnect the 66v lines from the bottom board, the one feeding the ground signal to the speaker and see if the top amp board still works with the scope ground. That would confirm the top amp board is working, i would think, and isolate the problem to the bottom amp board that feeds the ground signal to the speaker. Still have not really ruled out the 66v supply either. Last time i lifted the blue wire off each amp board one at a time the volts only went from 44 to 50 plus volts and not the 66 i had hoped for. This time i will disconnect both and check again.

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    Better Tone thru Mathematics bob p's Avatar
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    Enzo keeps at it with the double-posting.

    FYI there's a forum error in the php code, where there is a long delay in the processing of a post request, and instead of taking you to the "posted" page, the php script is kicking you back to the "view changes" page. If you're impatient, assume that things did not work, and you click on "submit" again then you'll repost. If you do that quickly, you'll even get the error message that you're only allowed to post once every 30 sec. That should be a dead giveaway that something is wrong.

    If you want to avoid the double post thing, you've got to stop clicking on the submit button when you get dumped back to the "view changes" page. One click on the submit button is all it takes, in spite of the fact that the glitch in the board is directing you to the wrong page. Now that you know this, you should be able to avoid double posting.

    Works for me.

    PS - perhaps this php glitch is related to why the forum keeps going offline every day. It's looking like the forum database needs to be backed up and the LAMP server implementation reinstalled, because the php script errors have been screwing things up for a while now.

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    "Stand back, I'm holding a calculator." - chinrest

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    Wait. You said if you connected your scope to the speaker terminals, the amp made sound. All I suggested you do was move the scope ground clip from the speaker to a ground point on the amp circuit. I don;t know from 66v or 44v or blue wires. Is the "ground" side of your speaker not supposed to be at ground potential?

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    Lifetime Member Enzo's Avatar
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    bob, I am not double clicking anything.

    I hit post once, just once, then it spins for a moment or so, yes longer than usual. Then it does one of two things. usually it just puts up a box asking if I want to leave the page, so I click yes. The other common thing it does is to show me the advanced dialog box and tells me I have to wait 28 more seconds to post again. It THINKS I asked to post again, but I did not click any posting buttons. At that point I usually just page back out of it, hoping it will just keep the original post and not put up the duplicate post it thinks I want. In other words it looks like it is asking me to hit post again, but I do not.

    I am doing nothing at all different from the way I post all the time on this forum for the last few years. I am not clicking post again in impatience.

    Now that you know this, you should be able to avoid double posting.
    bob, we can argue about things, and I don;t take it personally. But I resent the condescending tone of this.

    This problem has arisen on this board every so often over the years. I don't know what tboy does to clear it, I know I am not the only soul it affects. I don't know why it does not affect others.

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    Better Tone thru Mathematics bob p's Avatar
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    No condescending tone intended, but I have the same problem and I've learned to avoid it. I don't know if others have. Rather than hijacking Iv'e started a thread on this.

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    "Stand back, I'm holding a calculator." - chinrest

    "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

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    Quote Originally Posted by Enzo View Post
    I hit post once, just once, then it spins for a moment or so, yes longer than usual. Then it does one of two things. usually it just puts up a box asking if I want to leave the page, so I click yes.
    I think this is what leads to the double post (clicking yes to leave).
    When I have clicked 'submit', and get asked if I want to leave the page, I open the 'new posts' page (my bookmark) in a new tab. If I see my post at the top, I know it 'stuck' and just close the tab that is asking me if I want to leave.

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    Better Tone thru Mathematics bob p's Avatar
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    hijacker.

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    "Stand back, I'm holding a calculator." - chinrest

    "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

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    OK, So interesting. Disconnected the lower amp board -66 and the+44 (should be 66v) volt lines and had the scope wired to the speaker as before and the top amp sends signal through to the speaker so i guess that narrows it to the bottom amp board. Power supply still reads +44v after that. Thing is, even though the power supply only has +44 volts it seems to run the top amp just fine. So its gotta be on the lower board im thinking.

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    Last edited by greenmeanh1; 12-24-2017 at 02:40 AM.

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    Better Tone thru Mathematics bob p's Avatar
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    Quote Originally Posted by greenmeanh1 View Post
    Thing is, even though the power supply only has +44 volts it seems to run the top amp just fine. So its gotta be on the lower board im thinking.
    44 volts is plenty and will sound just fine ... until you need more than 44 volts.

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    "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

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    don't forget the joker g1's Avatar
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    The top amp and bottom amp terminology is very confusing, especially considering there are 2 amps in the unit, 1 good, 1 bad.
    Is there any way you can figure out what parts of Doug's schematic you are calling top and bottom amps?
    Or draw out an actual schematic for your unit using his as a template?

    As far as the power supply issue, check for AC voltage (ripple) on the 44V line and compare it to the working +66V rail.

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    So in the M 800 there are four amp boards, two on each side of the amp, or two amp boards on the left and two amp boards on the right. There is a pair of 1216`s and a pair of 2922s on each amp board`. Based on the drawing Doug posted it would appear that they are similar to the amp boards i have in my unit except i have four of them. I haven`t traced out the whole circuit yet for total comparison but they are for sure quite similar.
    Now in my particular case there is no common ground for the speaker as in most amps i have tried to work on. The speaker ground output is isolated from the chassis. It appears they pair two amp boards together to make one channel. The output of one of the amp boards ( the bottom one) goes to the ground speaker terminal, the other (top one) to the positive speaker terminal. I guess its like bridging two mono amps but that is a guess. I tested the good side of the amp and the ground is isolated on that side as well. Hope that helps to clear that up. Sorry i really suck at explaining this stuff.

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    Lifetime Member Enzo's Avatar
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    OK, so the amp is probably two amplifiers per channel and they are bridged. SO an amp for the positive and an amp for the negative. If one of those stops working, the thing will not make sound. But if you ground one of those outputs, then the other working side will power the speaker, though at half level.

    In this case then, you should never connect the scope ground to either speaker terminal as it may ground out the output of that amp. It only worked here because that amp side is dead. or so it appears to me. You ground the scope to the ground and view both terminals to see if they have output.

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    Diagram (corrected twice now)
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    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

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    Last edited by greenmeanh1; 12-24-2017 at 10:30 AM.

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    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.

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  34. #34
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    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.

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    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.

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