I would suspect Q2 rather than Q1. If the current is too high, I would suspect the CCS components. That would be Q2 and Q3 and surrounding components. Also check the value of R7.
Q1 may be also damaged by the excessive current though.
Q1 may be also damaged by the excessive current though.
Thanks ZM and BM.
Yes - Q2 close to the smoking R3/R4,
Can either of you please guide me on the procedure to test in situ w/ DMM diode mode, and values expected if good or bad?
Yes - Q2 close to the smoking R3/R4,
Can either of you please guide me on the procedure to test in situ w/ DMM diode mode, and values expected if good or bad?
I am not as smart as ZM so I can't give you an exact procedure, but since you have some good channels, probe the transistors' leads with your meter and compare the results between the bad and good board.
Also check the resistors for correct values.
Also check the resistors for correct values.
ggle is our friend, plenty of tutorials
bipolars can be proven 90% for functionality with diode test, while mosfets are proven for no-shorts..... which will cover 90% of possible ookup here
bipolars can be proven 90% for functionality with diode test, while mosfets are proven for no-shorts..... which will cover 90% of possible ookup here
Both of you super helpful. The Q2 for sure bad. And both Q2 and Q1 way inconsistent with the other 3 non-smoking healthy 🙂 PCBs
Removed Q2 and Q1 will check resistors next.
Removed Q2 and Q1 will check resistors next.
You guys bloody rock!
I swapped out the 0,68R R4, left in the R3 after measuring. Tacked in known good 240s from my stereo ACA build. Swapped out C1 and placed in one of the spare new 33uf from the original stock stereo ACA that went unused since I started the build at premium.
30VDC at both LPS output caps. Cranked the bias pots all the way down before I powered and the near Qs read 4V on all four boards.
1.5mv at both binding posts.
What do you advise now? I was going to cook for an hour come back and set bias maybe in the morning.
No magic smoke! I do have one LED that's unlit, Will need to resolve that.
I swapped out the 0,68R R4, left in the R3 after measuring. Tacked in known good 240s from my stereo ACA build. Swapped out C1 and placed in one of the spare new 33uf from the original stock stereo ACA that went unused since I started the build at premium.
30VDC at both LPS output caps. Cranked the bias pots all the way down before I powered and the near Qs read 4V on all four boards.
1.5mv at both binding posts.
What do you advise now? I was going to cook for an hour come back and set bias maybe in the morning.
No magic smoke! I do have one LED that's unlit, Will need to resolve that.
all good
now - output offset - you can't really expect any, having output cap as DC blocker
just as brain activity reminder
now - output offset - you can't really expect any, having output cap as DC blocker
just as brain activity reminder
Burned in this morning for an hour, set bias. Hooked up speakers, preamp + tuner.
It plays music. No hum either channel, but there is an intermittent crackle from the left channel. Haven't yet identified the fault with chopstick tapping.
Any hints on how to diagnose the crackle?
It plays music. No hum either channel, but there is an intermittent crackle from the left channel. Haven't yet identified the fault with chopstick tapping.
Any hints on how to diagnose the crackle?
visual inspection of wiring and soldering job
then power on your soldering iron
then power on your soldering iron
Update post ZM advisory, re-flowed both parallel left channel boards and did close visual inspection with magnifying lens.
Crackle still there, so proceeded to try to determine which PCB is the culprit on left channel, by depowering each individual board on that left side.
One is dead, the other plays w/o crackle. I suspect I may have fried the MOSFETs on that side.
Crackle still there, so proceeded to try to determine which PCB is the culprit on left channel, by depowering each individual board on that left side.
One is dead, the other plays w/o crackle. I suspect I may have fried the MOSFETs on that side.
Root cause identified on dead board. Toasted the MOSFETs. First I checked Q3 and Q4 both boards on the left channel (DMM diode mode and measured resistance between EBC). Good, so checked the Q1 and Q2 which measured bad. Uninstalled those awaiting delivery of replacements ETA tomorrow and observe cooked PCB sections.
Cautionary tale: make sure your fasteners and tapped heatsink holes are performing properly. Read the posts about how to drill and tap correctly. I’ve resolved the problem and hope to have the amp up this week.
Cautionary tale: make sure your fasteners and tapped heatsink holes are performing properly. Read the posts about how to drill and tap correctly. I’ve resolved the problem and hope to have the amp up this week.
Dual mono parallel ACA premium parts is now functioning well. I backed the rails down to 26V. With the replacement MOSFETS installed in the board that died, runs. Super quiet, even when preamp is off mute volume up with source muted. So far seems to have more headroom than stereo ACA premium parts w/ dual SMPS bricks. Thanks folks for your diagnostic help and constructive thinking. The aft boards / heatsinks run hotter than the forward area, possibly because the rear panel is much thinner than the heavy front panel. Chassis is a 4U with the upgraded sinks.
Jkiriakis, you mention that there may be more headroom with the power supply that you built, any other improvements or differences vs the dual smps?
Zamjazz27-
For clarity: dual SMPS applied to stereo ACA with Randy Thatcher filters. This configuration I still have. Second build is a dual mono parallel with a linear power supply 300va 12.5lb Swiss transformer non-toroidal draws 18Vdc dual secondaries. CRCRC layout large cap cans with power resistors. I don’t have the gear to extensively measure results the goal was good sound based on a lot of reading on this site.
Loaded the power supply yields .03VAC so very little ripple. Dead quiet between CD player tracks (I can hear my Furman conditioner hum).
Net net I plan to exchange the four ACA PCBs for two Aleph J PCBs and keep the LPS as is to start. Same 4U chassis. UMS sinks.
For clarity: dual SMPS applied to stereo ACA with Randy Thatcher filters. This configuration I still have. Second build is a dual mono parallel with a linear power supply 300va 12.5lb Swiss transformer non-toroidal draws 18Vdc dual secondaries. CRCRC layout large cap cans with power resistors. I don’t have the gear to extensively measure results the goal was good sound based on a lot of reading on this site.
Loaded the power supply yields .03VAC so very little ripple. Dead quiet between CD player tracks (I can hear my Furman conditioner hum).
Net net I plan to exchange the four ACA PCBs for two Aleph J PCBs and keep the LPS as is to start. Same 4U chassis. UMS sinks.
Further to this on the dual mono parallel ACA with premium parts. Now feeding this amp with a B1Korg buffer/pre, Source Sony CDP X777ES coax digital out to Monarchy Audio Digital Interface Processor 24/96 into simple Pro-Ject DAC BoxE. System sounding extremely pleasant and I'm finding myself turning it up to good effect. I'm happy with the LPS and the amp to the point that I expect to build the Aleph J boards very slowly carefully and deliberately while continuing to enjoy the ACA monos and not rush the transplant.