Thanks so much, also had the same problem of a blacked out little glass device with no idea what it was. Was cursing the double-diode marking as a silkscreen error, but it makes sense now!!!
Will scrape off the glue stuff, also had one burned out IRF740, which I replaced but have this dead oscillator board. Have ordered the DB4, fingers crossed.
Anyone else have success after replacing the DIAC and MOSFET?
I'm guessing the (now conductive) glue buggers up the circuit and/or DIAC fails causing the MOSFET to be stuck on and thus "shorting" into the transformer?
Will scrape off the glue stuff, also had one burned out IRF740, which I replaced but have this dead oscillator board. Have ordered the DB4, fingers crossed.
Anyone else have success after replacing the DIAC and MOSFET?
I'm guessing the (now conductive) glue buggers up the circuit and/or DIAC fails causing the MOSFET to be stuck on and thus "shorting" into the transformer?
I have PSB Subsonic 6i woofer with blown glass fuse and missing C1 & C2 Capacitor and Q401 & Q402 Transistors. Can you help me to solve the issue?
Is this acid-cure silicone by any chance? There are several types of silicone, the acid-cure type is completely unsuitable for any electronics (its used as bathroom sealant), as it cures full of conc. acetic acid which leaches out over time and attacks most metals. Conc. acetic acid is hygroscopic attracting moisure, hence the conductivity.
Its worth knowing this if you ever want to employ silicone rubber or filler for circuits...
They cannot be replaced with a fixed voltage supply. Repair the supply that came with it or send it out for repair.
Even acid based silicone is better than that Chinese yellow glue. It will corrode components, but it doesn't become conductive.
Yellow Glue
OP did you solve this problem by replacing these two parts (or something else)? I might have the same exact failure. HSU VTF2 MK3 BASH amp
I have two HSU VTF-2 MK3 subs with BASH amps purchased new from HSU around 15 years ago that both failed (blowing fuses and unable to power up). The first amp failed around 10 years ago and was replaced with a new amp; the second amp just failed recently. The Q401 IRF740 MOSFET failed (all leads shorted) on both amps and after extensive disassembly of one power supply board no other failed parts were found. After some quick checks on the other amp I went ahead and replaced Q401. The amp now works perfectly although it has only been running for a few hours so far. The DSP 104 varistor on each board appears to be good - one of them measured 10 ohms out of circuit; the second one was 13 ohms. I'll be ordering two more IRF740 MOSFETs along with new electrolytic caps to repair the other power supply and hopefully have similar success.
Two N-channel mosfet ( IRF730 ) changed to a new ones also two non-polar capacitors ( polypropylene) where changed, there ESR increased. Finally few resistors where changed ( 200K ) in the control card, now everything ok the smps came back to alive.
