Mackie Onyx 1620 Psu fault - Page 1
Forum section: electronics / repair

author: miksepult
author_rank: Newbie
timestamp: June 11, 2018, 12:02:04 pm
content: Hi! I have a Mackie Onyx 1620 mixer which is not working correctly. I have narrowed it down to the PSU. The lights are flashing, and you can hear a clicking noise (about 1 time per second. I've changed all of the electrolytic capacitors, that helped, but it still didn't work. (It helped a bit). I started mesuaring voltages, and when I tried to mesure one of the diodes (think it was D2), it made a spark and suddently stopped working.Do you think that you could help me to figure out what's wrong?(Look at the schematic and video below)Regards Benjamin

author: xavier60
author_rank: Super Contributor
timestamp: June 11, 2018, 11:02:21 pm
content: Check all of the outputs for any pulsing voltage. If there is, then the power supply isn't totally dead and you might now have a shorted output diode as well as the original fault which possibly involved the 15V Bias supply.Are you using an isolation transformer? What other test equipment do you have?Don't power it up with anything removed that will break the regulation loop.

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 12:01:53 pm
content: Quote from: xavier60 on June 11, 2018, 11:02:21 pmOk, thanks! There isn't any voltage at the outputs, but the voltage reaches the transformer. I don't now if it's an isolation transformer. I have just a digital multimeter. (UNI-T UT132E)RegardsBenjamin

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 12:06:46 pm
content: Here are some pictures:

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 12:07:33 pm
content: Some more:

author: xavier60
author_rank: Super Contributor
timestamp: June 12, 2018, 01:30:47 pm
content: Did you check for shorted output diodes?T1 is an isolating transformer.

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 01:40:51 pm
content: Quote from: xavier60 on June 12, 2018, 01:30:47 pmOk. I've tried to mesuare the diodes. Some of them passed voltage through the wrong way. Mesuared with the diode function on the multimeter. Was like 1k from positive to negative, and 200 from negative to positive.

author: xavier60
author_rank: Super Contributor
timestamp: June 12, 2018, 02:01:08 pm
content: Quote from: miksepult on June 12, 2018, 01:40:51 pmIt's normal for schottky diodes to measure a low forward bias voltage. The 1K reading could be because of resistors in circuit.Shorted diodes usually measure less than 1 ohm.U1, TOP249 is suspect. Check all nearby resistors before replacing U1.

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 02:25:55 pm
content: Quote from: xavier60 on June 12, 2018, 02:01:08 pmOk, thanks! Is it possible that i have destroyed the top249 when i tried to mesuare the diode? I've ordered a top249, so I'll see if that fixes it. 🙂

author: xavier60
author_rank: Super Contributor
timestamp: June 12, 2018, 02:36:22 pm
content: Yes, it's possible, not for certain. Also check D16 and R42.It is also possible for the opto-coupler, U3 to be responsible for the original problem.

author: xavier60
author_rank: Super Contributor
timestamp: June 12, 2018, 02:43:02 pm
content: Be certain that it is the TOP249Y to get the correct package type.

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 02:44:23 pm
content: I'll check that! 🙂Will come back with some more info when I've changed the top249 🙂

author: miksepult
author_rank: Newbie
timestamp: June 12, 2018, 02:45:12 pm
content: Yes, I ordered the top249y.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 12, 2018, 10:06:08 pm
content: R23 is cooked, possibly because you slipped making measurements, it is likely to have caused other damage.I'd be checking/replacing:D2, D3, D7, D8, D9, D11, R20, R21, R22, R23, U3, U1.For the starting point problem check:C55, D16, R42, R1 to R9.Also just because they have run hot check solders on R26 to R35.

author: xavier60
author_rank: Super Contributor
timestamp: June 12, 2018, 10:54:44 pm
content: D7,R20,R21,R22,R23,D8 and the opto-coupler form the output voltage sensing part of the regulation loop.Although the TOP249Y has a protection feature that will cause it to not run continuously with an open regulation loop, it's still possible for it to be damaged by over voltage pulses on the Drain pin.Because opto-couplers can't be easily tested, it must be replaced also.