Blackstar HT pedal repair

[Yazoo]

I've just repaired a Blackstar HT Dual pedal bought as not working. I previously posted about trying and failing to repair a Blackstar HT Delay pedal. It was the same problem with the SMPS section used to power the 12AX7. This time the pcb hadn't been burnt. Symptoms were that the internal power indicator led was flashing and there was no power on the 7915 negative regulator using the included power supply. I think it was trying to pull too much current and the psu couldn't cope - actually a good thing.

When I used a bench power supply capable of greater current, the Mosfet IRF830 started to cook. I found a 1M resistor on pin 2 of the UC3843 was open. I removed the inductor which measured 430 uH, not 470 uH. I also went back and measured the inductor from the HT Delay and this came up as a very low value resistor, not an inductor.

So I replaced the inductor and resistor and Mosfet and that did the trick. It is now working properly. It looks like the inductor was the main problem. Hope this helps if you have the same problem.