Hi there,
I have an assemblage 2.7 dac that blew its transformer and fuse while i was on holiday.
I replaced the psu with the identical model and the lights all came on so i thought everything was fine.
However after leaving it on for several minutes it started to smell and slowly started to bulge like the previous transformer had.
When I started hearing "bubbling" noises from within the transformer i turned it off.
Surprisingly the fuse didn't blow.
Ive thoroughly checked the pcb on both sides and all components and cant see any further damage.
Does anyone have any ideas what could be wrong and how to fix it?
I have an assemblage 2.7 dac that blew its transformer and fuse while i was on holiday.
I replaced the psu with the identical model and the lights all came on so i thought everything was fine.
However after leaving it on for several minutes it started to smell and slowly started to bulge like the previous transformer had.
When I started hearing "bubbling" noises from within the transformer i turned it off.
Surprisingly the fuse didn't blow.
Ive thoroughly checked the pcb on both sides and all components and cant see any further damage.
Does anyone have any ideas what could be wrong and how to fix it?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
hang on, so you didnt just turn it off when it started to bulge :S by thoroughly checking and you cant 'see' any damage, do you have a multimeter? this sound like there is an internal short in something or a bad cap and you simply applied power to something that is already shorted out and of course it just repeated the fail condition like last time. i'm unfamiliar with the dac so aside from recommending you go over the thing with a meter and give us some better pictures, i'm afraid I cant help that muchand BTW the pictures although they say under them are high resolution are just the same size as the previews when you click on them ie. they dont enlarge when you click, so its hard to see anything. but yeah doesnt sound like we would be able to see anything anyway.
We can probally help you find the problem but you must try to locate a schematic to post. There is somethng very wrong indeed! I wonder what exactly you replaced. Did you find a used part? Both of the transformers that got hot/smelly/buldgy are probally toast. Also we still have no idea what the oridginal problem was. I will have a stab at finding a schematic.
Ive finally managed to get a psu schematic.
Hopefully its readable.
Can anyone help with this?
2shared - download assemblage psu schematic.jpg
Hopefully its readable.
Can anyone help with this?
2shared - download assemblage psu schematic.jpg
I had problems with the last upload so if it doesnt work try downloading this jpeg.
Its 7.2megs so should be quite readable;
assemblage psu schematic.jpg
Its 7.2megs so should be quite readable;
assemblage psu schematic.jpg
I have a unit with the exact same issue, but the links for the schematics are too old and do not work anymore. Do any of you have the schematic and could share it please?
So far I have found a low resistance across D102 / C102 after removing them (60 ohm). The LM317s, LM337s and the 7812 seem healthy. My guess is either an electrolytic cap short or a PCB inner layer short. Next step is to remove the transformer and the electrolytic caps. I hope to document the debug here in case someone else in the future has the same issue
So far I have found a low resistance across D102 / C102 after removing them (60 ohm). The LM317s, LM337s and the 7812 seem healthy. My guess is either an electrolytic cap short or a PCB inner layer short. Next step is to remove the transformer and the electrolytic caps. I hope to document the debug here in case someone else in the future has the same issue
Attachments
Turns out the issue was both the electrolytic cap and a PCB short. Seems like one of the electrolytic caps leaked and that caused a short from - to GND. The short burned the PCB and then caused a short to the power plane in layer 2.
After cleaning all the carbon and electrolyte residue, I drilled out the damaged area of the PCB but the short was still there. Looked at it through a thermal camera while powering the rail with a constant current source at 100mA to not break anything further. Found the short also existed right under the capacitor pad going to layer 2. Had to drill out the pad completely.
After that, filed the holes to avoid copper burrs and filled them with non conductive epoxy to avoid any dendrite growth in the future. Drilled a hole in the epoxy for the cap and replaced the broken trace. You can see the fix progression attached.
Finally powered the rails with an external power supply and got a normal current draw <200mA per rail at 15V. All rails for the digital and analog section came up and measure nominal.
Next step is to replace the broken parts (transformer, fuse, electrolytic caps and rectifier diodes) and check for sound output.
After cleaning all the carbon and electrolyte residue, I drilled out the damaged area of the PCB but the short was still there. Looked at it through a thermal camera while powering the rail with a constant current source at 100mA to not break anything further. Found the short also existed right under the capacitor pad going to layer 2. Had to drill out the pad completely.
After that, filed the holes to avoid copper burrs and filled them with non conductive epoxy to avoid any dendrite growth in the future. Drilled a hole in the epoxy for the cap and replaced the broken trace. You can see the fix progression attached.
Finally powered the rails with an external power supply and got a normal current draw <200mA per rail at 15V. All rails for the digital and analog section came up and measure nominal.
Next step is to replace the broken parts (transformer, fuse, electrolytic caps and rectifier diodes) and check for sound output.
Attachments
