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Thread: Wurlitzer 200A keeps blowing .5 main fuse

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    Wurlitzer 200A keeps blowing .5 main fuse

    Hello! I have a Wurlitzer 200A that will blow the .5 main fuse as soon as it's turned on. I have checked all transistors, caps, replaced diodes etc... and everything checks out! I've never ran into this issue before and I've worked on a good number of Wurlitzers. Not sure what to make of this

    If anyone out there has had a similar issue please let me know what you did to eliminate it. I also checked for shorts and to no avail.

    Any help is appreciated! Thanks!

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    Lifetime Member Enzo's Avatar
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    1/2A slow blow, right?

    If we already checked for shorted rectifiers in the power supplies and shorted output transistors. AND we checked that none of the power supplies are shorted to ground, then start at the start. Isolate the problem. In the schematic I have the transformer has a couple red wires plus center tap for the 22v supplies and a blue wire for the high voltage. They connewct to the board at terminals X1, X2, X3. Disconnect them and see if the fuse holds. If the fuse still blows with them disconnected, you either have a bad power transformer or a short in the primary wiring. I suppose a shorted pilot light assembly or a shorted 0.01uf cap across the primary could be bad.

    If the fuse no longer blows, then connect the blue wire back up. The red/yel center tap needs to be there too, you didn't need to disconnect it anyway. Now does it blow fuses with just the blue wire? If so, then the HV circuit has some issue. Otherwise, move on to reconnecting the red wires, just one at a time.


    In the power amp, are the two fuses there? Are they OK? Pulling them ought to disable the power amp, I;d think.

    Your basic supply is a pair of 22v rails, but there is also that IC making 15v out of it. Schematic shows a house number. Is it a 723 chip by any chance? I see its 15v output going to several circuits plus "white wire to preamp" at terminal 19. is that shorted to ground?

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    Supporting Member Jazz P Bass's Avatar
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    Are you using the correct fuse? (slo-blo may be needed)
    Have you attempted to isolate the power supply?
    If you have only the transformer in circuit & it pops a fuse, then the transformer is suspect.
    There are (2) 2200 uf caps on the supply.
    If one or both are bad, that would pull current at power on.
    http://www.vintagevibe.com/misc/Elec...e%20Manual.pdf
    http://www.ep-service.nl/joomla/down...rli_pb_200.pdf
    Attached Files Attached Files

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    Quote Originally Posted by Enzo View Post
    1/2A slow blow, right?

    If we already checked for shorted rectifiers in the power supplies and shorted output transistors. AND we checked that none of the power supplies are shorted to ground, then start at the start. Isolate the problem. In the schematic I have the transformer has a couple red wires plus center tap for the 22v supplies and a blue wire for the high voltage. They connewct to the board at terminals X1, X2, X3. Disconnect them and see if the fuse holds. If the fuse still blows with them disconnected, you either have a bad power transformer or a short in the primary wiring. I suppose a shorted pilot light assembly or a shorted 0.01uf cap across the primary could be bad.

    If the fuse no longer blows, then connect the blue wire back up. The red/yel center tap needs to be there too, you didn't need to disconnect it anyway. Now does it blow fuses with just the blue wire? If so, then the HV circuit has some issue. Otherwise, move on to reconnecting the red wires, just one at a time.


    In the power amp, are the two fuses there? Are they OK? Pulling them ought to disable the power amp, I;d think.

    Your basic supply is a pair of 22v rails, but there is also that IC making 15v out of it. Schematic shows a house number. Is it a 723 chip by any chance? I see its 15v output going to several circuits plus "white wire to preamp" at terminal 19. is that shorted to ground?

    I removed the X1, X2, X3 points. Hooked up the blue for the high voltage and fuse was fine. Went to hook up one red wire to X1 and the fuse blew. Now I need to get another 1/2 amp TR fuse as that happened to be the last one! LOL!!! Figures. Any suggestions?

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    Quote Originally Posted by Polyneux View Post
    I removed the X1, X2, X3 points. Hooked up the blue for the high voltage and fuse was fine. Went to hook up one red wire to X1 and the fuse blew. Now I need to get another 1/2 amp TR fuse as that happened to be the last one! LOL!!! Figures. Any suggestions?
    Don't connect the red wires while the unit is turned on. Build yourself a light bulb limiter to save your fuses.

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    Supporting Member Jazz P Bass's Avatar
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    Quote Originally Posted by Polyneux View Post
    I removed the X1, X2, X3 points. Hooked up the blue for the high voltage and fuse was fine. Went to hook up one red wire to X1 and the fuse blew. No
    You really should have the center tap (X4) hooked up when connecting X1 or X2.

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    No, I made sure the unit was turned off before connecting anything and trying again.

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    Center Tap was connected. Never removed the yellow/ red striped wire or ground.

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    Lifetime Member Enzo's Avatar
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    OK, so your +22 or -22 supplies are involved. I;d check those rectifiers again for shorts. D2,3,4,5. Then also check to see if the caps C28, C29 appear to be shorted to ground, and again, make sure that +15 supply is not shorted, especially as it connects to the preamp board.

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    Hi Enzo, I'm experiencing the same problem on my 200A and have followed your advice. I find that after I have disconnected the 2 red and 1 blue wire coming from the transformer the fuse no longer blows. If I reconnect the blue wire to the board then the mains fuse blows.

    I have very basic knowledge of electronics so excuse my ignorance with this stuff. I also used my multimeter to try and check what voltage was coming out of the transformer by placing one probe on a red and the other on a blue, I did not get any reading at all, though I'm not sure if I'm putting the probes on the correct wires anyway

    Do you think you could advise what may be causing the problem?

    Thanks
    Ali

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    Lifetime Member Enzo's Avatar
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    The blue wire is the high voltage. If you can connect the red wires and no fuses blow, that is good. If the blue wire blows fuses, then check the diode D6 for shorts, and also explore the connections around that for any possible short to ground. That makes a 150vDC supply, but after the rectifier is a 56k resistor, so even if the first cap, C30 were shorted, that resistor would limit current to under 2 milliamps. That won't blow fuses. And thus anything further down the line through those 1 meg resistors even less likley. SO I have to suspect something like a loose wire, a blob of solder, some piece of loose hardware touching, something else causing a short to ground.

    That is where I would start.

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    I had a same issue, checked the usual culprits-power caps,transistors,diodes etc-even took it to a proper tech and he could not find what was wrong either. Fuse did'nt blow when I disconnected the transformer.In the end it was broken tracks on the circuit board, I repaired all the tracks to do with the power section and it worked.

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