Yorkville AP812 powered mixer

[xtian]

Powered mixer on the bench, non-op. The main bridge recto is working (green check on my diagram), making +70/-70vDC. But the +15/-15/+24 rails are not working, because fuse F1 and F2 are open (circled in red). Before I replace these fuses, I want to know if there is other trouble that is causing excessive current.

Nothing looks burned. Filter caps appear OK to the eye. If I start up without my bulb limiter, the amp draws a big surge of current, tripping my UPS momentarily. Possibly this is just because of the large capacitance of the reservoir. It settles right down and draws 60 watts or so (500mA) while running.

What else should I check before replacing the fuses?


Full schematic is available here: Yorkville

[52 Bill]

Before I replace these fuses, I want to know if there is other trouble that is causing excessive current.

There is a reason the two fuses blew, it is not often that they just go for no reason.

If you power up with your limiter do the two fuses hold? If they do, read the voltages of the three low voltages and see if any of them is low or missing (all of the voltages will be low with the limiter).

[xtian]

I can't replace the fuses yet--they're small, inline packages soldered in. Will have to order. But I have jumpered them (using bulb limiter!) and current did not run away. Voltages are: 5.0, 25.7, -14.6, 13.8 (yes, there is a 5v rail I forgot to mention eariler).

[52 Bill]

I can't replace the fuses yet--they're small, inline packages soldered in. Will have to order. But I have jumpered them (using bulb limiter!) and current did not run away. Voltages are: 5.0, 25.7, -14.6, 13.8 (yes, there is a 5v rail I forgot to mention eariler).

So is everything working correctly now on the limiter?

[xtian]

With the limiter, the voltages appear to spec, as listed above, Though the main +70/-70 rail is only 48v, due to the limiter. I ordered new fuses, expected Wednesday. But if there are any other common modes of failure, would appreciate a heads up. Thanks, Bill!

[dbtech]

Something that you might consider while waiting for the more expensive fuses to arrive would be to remove the existing fuses and install wires where the fuses were attached. You can then connect the wires to inexpensive common fuses of the same amperage, like AGC 1.5 (or AGC 1 to start with). The AGC type is so common, you can afford to go through many without much cost if more troubleshooting is required, and they are available everywhere. dan

[xtian]

Thx, dan.