Hello,
Im currently trying to fix my Orange Terror Bass 500w which has faulty Fqa28n50. They go short right after i turn the unit on. It takes the 6.3a fuse but also the 2 mosfets....
I attached the schematic, it uses a ir2153. What i dont get is when i power the ic with 12v, i have my gates acting on my mosfets but only a 15v amplitude oscillation.
I check everything on the psu and everything look ok so i might be playing with fakish component either the driver or the Mosfet...
What do you think could go wrong ? Its obviously on the primary side, it goes bad with no loads.
Cheers
Im currently trying to fix my Orange Terror Bass 500w which has faulty Fqa28n50. They go short right after i turn the unit on. It takes the 6.3a fuse but also the 2 mosfets....
I attached the schematic, it uses a ir2153. What i dont get is when i power the ic with 12v, i have my gates acting on my mosfets but only a 15v amplitude oscillation.
I check everything on the psu and everything look ok so i might be playing with fakish component either the driver or the Mosfet...
What do you think could go wrong ? Its obviously on the primary side, it goes bad with no loads.
Cheers
I can't give you any definite reasons but I have worked on many many SMPS over the years and many issues are caused by failed/failing caps. These would typically be the small electrolytics on the primary such as C1. That would be a classic and typical failure item. Measuring just the value tells nothing as they often fail with a high E.S.R.
High value resistors such as the 470k are another possible issue. Check them out of circuit. Some types such as metal oxide types can also go low in value as well as going high.
Check for any shorted rectifiers on the secondary side.
Any diode replacements have got be suitable and that means high speed soft recovery types. The UF4004 for example is nothing like the common IN4004
If you are testing the unit with nothing connected to the PSU outputs then use a DBT to try and limit any damage.
High value resistors such as the 470k are another possible issue. Check them out of circuit. Some types such as metal oxide types can also go low in value as well as going high.
Check for any shorted rectifiers on the secondary side.
Any diode replacements have got be suitable and that means high speed soft recovery types. The UF4004 for example is nothing like the common IN4004
Not sure what you mean here. If you power the IC externally from 12 volts the expected drive voltage would be around 0 to 12 volts in amplitude. Not sure how you come to see 15 in that scenario.
If you are testing the unit with nothing connected to the PSU outputs then use a DBT to try and limit any damage.
Put a 10W resistor as a dummy load on the outputs, some SMPS act funny without load.
Even a filament lamp of 40W on each output will work as a dummy load.
Even a filament lamp of 40W on each output will work as a dummy load.
Alot of times if you're smoking fets, its due to gate oscillation but if the circuit is push pull, there may be a timing issue making one half conduct at the same time as the other. That may me a cap or a dampening diode, but also the driver stage.
Check all components, start here:
Once the components check okay, I would load the SMPS before powering it on...
Good luck.
Once the components check okay, I would load the SMPS before powering it on...
Good luck.
Could be the ir2153 is damaged too ?
I did a lot of work with a class d amps and most often if the mosfets went they took the driver IC too.
I did a lot of work with a class d amps and most often if the mosfets went they took the driver IC too.
No protection zeners across gate and source - a very good idea to add these to make MOSFETs robust - must be mounted right close to the package to be effective against transients. Very high dV/dt values happen with high voltage MOSFETs, and the gate-drain capacitance couples that to the gate, so shunt protection on the gate becomes important. For instance a 100V 30ns transient would couple about 0.25A to the gate, which would put 15V across the 62 ohm resistor, if there isn't a 20V zener between gate and source that's enough to pop the gate oxide (it only takes nanoseconds to do this)
And of course observe proper anti-static precautions handling any MOSFET.
And of course observe proper anti-static precautions handling any MOSFET.
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