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Comptech
| | Posted on Saturday, November 01, 2003 - 8:47 am: | 
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I have a maco 200 and when ever i is powered up it either blows the fuse in the box or kick the breaker on the power strip. I believe its in the transformer but am not sure. the power transformer has 5 smaller wires (2 red,2 black, and a yellow) and 2 larger wires (2 green) coming from a single location out of the front side of the transformer. I've tried unsoldering these wires and the only ones that change anything are the 2 black wires which when unsoldered , the fan will run but the tubes dont lite up. does this sound like a transformer problem or something else? what is each of the transformer used for? any help or advise would be greatly appreciated. |
Jp1116
| | Posted on Monday, November 03, 2003 - 2:37 pm: |
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It's been awhile since I've seen one but I'll give it a try. The two green wires are the 12 volts AC to run the tube filaments. The 12 volts to run the relays are also taken from these wires and rectified to provide the required DC voltage.
The two red wires are the high voltage secondary and are used on the three final tubes when the amp is run on high. The yellow wire provides a lower voltage to the finals for the low power and voltage for the driver tube on both power levels.
The two blacks should be the primary and be connected to the AC power line through the fuse holder and the switch. The fan will still run when you disconnect the transformer because it runs off 120 VAC and does not rely on the transformer.
I would suspect you have bad filter capacitors or a bad diode in one of the rectifiers rather than a bad transformer. Since the plate voltage is on the tubes all the time one other possibility is a bad tube.
You can check all of this out without turning on the amplifier. Be sure you discharge the filter capacitors if they don't have a bleeder resistor (check anyway) and then check the diodes in the bridge rectifier the the diode coming off the yellow wire. Also the one on the green wire. After that check your filter capacitors. If all of these parts are good you can check the tubes on a tube tester for shorts. If you get this far and don't have a tube tester and the other parts are good, you can pull the plate clips off the top of the tubes and turn it on. If it doesn't blow the fuse it is probably a tube. If it still does, probably the transformer.
Hope some of this rambling helps, if it is clear as mud let me know and I can give you more detail. If you are not familiar with working on amps don't do anything until you understand how to work safely and discharge the high voltage. |
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