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I have a Studiomaster Trilogy 166 in house with one working and one dead external power supply type EP7-N. No schematics to be found, but it's a pretty straight forward supply. It has two sections, a 1A bridge rectifier, diodes and caps for the 48v supply, and another rectifier, diodes and caps for the +/- 15v regulators. The secondary of the PT has two windings. One supplies the 48v side through a fuse. The other winding supplies the +/- rails through two fuses, one on each AC leg of the bridge rectifier, and both of these fuses were blown.
Since it is nice to have working one to compare to, I checked everything I could think of and did side by side comparisons, but found nothing suspect. All the diodes, both rectifiers, filter caps, and regulators looked OK. So I put it on my bulb limiter and switched it on. Bulb barely lit up, the board lights came on, so I switched it off and plugged direct into the AC and it blew both fuses again (albiet they were 500mA, not the 1.6 amp it calls for). more checking, still nothing, except for one thing. I noticed a washer securing one of the regulators on the back of the heatsink was touching the ground buss, and I was getting 10 or so ohms from it to ground, so I loosened and corrected that, but I don't think it was the problem because it looks like everything is insulated. But to satisfy my OCD, I remedied it.
Then I put it back on the bulb limiter and have all my voltages on the connector, +/-15v and 48v. I don't understand this. I don't have the proper value fuses on hand, but from what I have described I half expect it to still be blowing those fuses since I haven't actually found anything wrong. So, my question is, how could this be? Given the inexpensive parts, I am almost set to order up a LM7815, LM7915, and a bridge rectifier, but I know Enzo won't care for that approach.
Is it possible that one of these devices is working on the bulb, but shorting under actual load?
Since it is nice to have working one to compare to, I checked everything I could think of and did side by side comparisons, but found nothing suspect. All the diodes, both rectifiers, filter caps, and regulators looked OK. So I put it on my bulb limiter and switched it on. Bulb barely lit up, the board lights came on, so I switched it off and plugged direct into the AC and it blew both fuses again (albiet they were 500mA, not the 1.6 amp it calls for). more checking, still nothing, except for one thing. I noticed a washer securing one of the regulators on the back of the heatsink was touching the ground buss, and I was getting 10 or so ohms from it to ground, so I loosened and corrected that, but I don't think it was the problem because it looks like everything is insulated. But to satisfy my OCD, I remedied it.
Then I put it back on the bulb limiter and have all my voltages on the connector, +/-15v and 48v. I don't understand this. I don't have the proper value fuses on hand, but from what I have described I half expect it to still be blowing those fuses since I haven't actually found anything wrong. So, my question is, how could this be? Given the inexpensive parts, I am almost set to order up a LM7815, LM7915, and a bridge rectifier, but I know Enzo won't care for that approach.
Is it possible that one of these devices is working on the bulb, but shorting under actual load?
) Like a good scout, be prepared.
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