Hi all, I've got a Hifonics BXX4000.1D that (mostly) has no output, no oscillation on the output section.
After it's been off for a long time, it'll sometimes work for a little bit, and seems to produce clean output, R/R oscillation waveforms look clean, then the output sections stop oscillating.
Power supply remains on, relays are closed, and it does not go to protect. Voltage going into the output inductors is zero (none of the output devices conducting or leaking). Cycling the remote at this point gives what looks like a normal startup, power supplies start properly but no attempt at all at output oscillation, not so much as a single gate pulse anywhere on the outputs.
Nothing is getting inordinately hot according to my thermal cam, and the +/- 15V and +/-5V supplies going into the modulator board look OK, even when it's not oscillating. The ground-coupling circuit is good.
Anyone seen this and figured out what causes it? Thanks!
After it's been off for a long time, it'll sometimes work for a little bit, and seems to produce clean output, R/R oscillation waveforms look clean, then the output sections stop oscillating.
Power supply remains on, relays are closed, and it does not go to protect. Voltage going into the output inductors is zero (none of the output devices conducting or leaking). Cycling the remote at this point gives what looks like a normal startup, power supplies start properly but no attempt at all at output oscillation, not so much as a single gate pulse anywhere on the outputs.
Nothing is getting inordinately hot according to my thermal cam, and the +/- 15V and +/-5V supplies going into the modulator board look OK, even when it's not oscillating. The ground-coupling circuit is good.
Anyone seen this and figured out what causes it? Thanks!
With the black meter probe on pin 17 of the driver board (negative rail), what is the DCV on pins 6 and 16 when the amp produces oscillation and when it does not?
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Both seem to be the same within a couple mV, probably margin of error with my two meters. When oscillating, climbed up to 3.191 over a few seconds, then drifted down to 2.75 over a minute or so, then started climbing fairly consistently over several minutes, maxing out at 4.59. Then, while still oscillating, started dropping rapidly, oscillation stopped somewhere around 2.2V and the voltage went bouncing around between 0.58 and 2V. I had a scope on it too, and the movements look like noise (scope trace attached). It started oscillating again briefly during the large spike on that trace.
Attachments
It should have a muting circuit similar to the attached diagram. Find and pull the equivalent of Q51 and check it very carefully for leakage.
Looks like it was indeed Q51 (A1381). My bench supply only goes to 130V, no leakage seen, but replaced it anyway and the amp has been running stable for a couple hours now. Perhaps desoldering traumatized it enough to get rid of the leakage, or there was some invisible flux residue around or something. The pin 6/16 voltage is now quite stable at 4.55, that seem about right? I'm going to let it run for a day or two before I pronounce it fixed, but it looks good so far. Thanks much!
Yes. That's about right. When Q52 releases, the two ICs pull up internally and the voltage ends up near 5v. As long as it's over about 2.1-2.5v, the IC will produce output. 4.5v is easily high enough.