Thanks chaps, a few seconds into the video I realised my mistake, I had been working in mV not V so that my initial Vb was 1.5mv!!! Heatsinks now warming the house up nicely.
I finished assembly the ACA mini but on the right channel I have 0v on v0 I found no voltage from c2+ to gnd and 24v from c1+ and gnd, what have I check?
Finished up the ACA mini Clone- All biased up - working well - stoked. Placed it on a wood base with washers and alloy screws. Now SMPS flashes and the left channel IRF520 heatsink gets hot almost instantly upon power up. Slight smell of burning, no smoke. Might have tweaked the PCB when putting it down? Would love some thoughts about what might have occurred - and remedies. Thanks!
Washer contacts were exclusively on the PCB pad? 1 on top and 3 under to clear heat sink under-stud. Wood screw is alloy. Tightened to very low torque. Wood sections were not the permanent solution, but wanted something to grab other than the PCB.
Pics!
Pics!
Attachments
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If none of this looks like an obvious problem - I’ll re-solder the IRF520 tonight and send an update. Wasn’t sure if slight bending of the PCB could develop fissures across layers? Certainly a solder joint could have failed - just wasn’t sure how that would effect the circuit and PS.
Thanks again!
Thanks again!
Stating the obvious - but check for bad solder joints. I lost volume in 1 channel and started replacing parts. Got fooled because after one replacement the weak channel came back. Then it went bad again, despite another replacement. Finally found an intermittently bad solder joint in C4 which fixed the problem.
I'll add another suggestion: carefully look at the schematic and the PCB and try to understand what might be causing your issue. This may guide your investigation more efficiently. Best of luck and keep us informed! - David
Because the PCB is dual-sided, it may not be obvious where the Vb and Vo points on the PCB relate to the schematic (at least it was not obvious to me, mostly because prior to this, I've only worked on BJT-based designs). I had marked up the schematic with the Vb and Vo points to help me understand better, and post it here in case it is of use to others.
Thank you, David - obvious, but point well taken!
Re-soldered IRF520 Q4 - turned on and no PS hiccup - but still instant heat on Q4 and R9 .75ohm - re-soldered R9 - turned on and getting smoke which seem to come from that resistor. Quickly checked VO - registered 24v before I pulled power.
Kevin - straight down pics uploaded! (Edited) Thank you for taking a look!
Re-soldered IRF520 Q4 - turned on and no PS hiccup - but still instant heat on Q4 and R9 .75ohm - re-soldered R9 - turned on and getting smoke which seem to come from that resistor. Quickly checked VO - registered 24v before I pulled power.
Kevin - straight down pics uploaded! (Edited) Thank you for taking a look!
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From the pictures of the back side, to me it looks like the solder joints on the Drain and Gate of QL4 are touching.
If you have 24Vdc at Vo (instead of about 1/2Vcc) would seem to be an issue with Q3 being short circuit between D-S
We can’t see the solders on Q3 because that big 1uF is hiding everything...
Eric
We can’t see the solders on Q3 because that big 1uF is hiding everything...
Eric
Yes, agreed - big cap is not a window!
Thanks for your thoughts. I’ll take a look at the joints again with a magnifying glass.
Detail shots:
Thanks for your thoughts. I’ll take a look at the joints again with a magnifying glass.
Detail shots:
Thanks Zen Mod. Very helpful.
I believe Eric is right, Q3 might be the culprit with the short, but please bear with me to validate based on the DMM continuity buzzmeter. This is my first Mosfet troubleshooting rodeo. I've re-soldered all Mosfets to minimize possible solder contact before this test.
Left Channel
Q3 - Beeps across all pins
Q4 - Beeps across 2 rearward facing pins (toward input/output/power side of board) - I believe the drain and gate?
Right Channel
Q3 - Beeps across first and last 1 & 3 pins - drain and source
Q4 - Beeps across first and last 1 & 3 pins - drain and source
When I measured Vo across both channels
Left channel receives 24 volts, can be modified by pot to lower voltage
Right channel shows essentially zero voltage.
Please let me know what you think, and sincerest of apologies for not being especially knowledgeable in this arena. Worst case I can purchase a new ACA mini essentials board to get a new matched set of Harris mosfets, when they hit the store again. This is all good learning for me, but my stomach turns knowing the mosfets rare status. 🤢
I believe Eric is right, Q3 might be the culprit with the short, but please bear with me to validate based on the DMM continuity buzzmeter. This is my first Mosfet troubleshooting rodeo. I've re-soldered all Mosfets to minimize possible solder contact before this test.
Left Channel
Q3 - Beeps across all pins
Q4 - Beeps across 2 rearward facing pins (toward input/output/power side of board) - I believe the drain and gate?
Right Channel
Q3 - Beeps across first and last 1 & 3 pins - drain and source
Q4 - Beeps across first and last 1 & 3 pins - drain and source
When I measured Vo across both channels
Left channel receives 24 volts, can be modified by pot to lower voltage
Right channel shows essentially zero voltage.
Please let me know what you think, and sincerest of apologies for not being especially knowledgeable in this arena. Worst case I can purchase a new ACA mini essentials board to get a new matched set of Harris mosfets, when they hit the store again. This is all good learning for me, but my stomach turns knowing the mosfets rare status. 🤢