Blackstar HT-Delay

Yazoo55 · Post by **Yazoo55** » 03 Apr 2021, 17:14

I bought this pedal “for parts/not working” off eBay. I have disassembled it and it was immediately obvious something nasty had happened on the lower board in the power section. There was a partially toasted 47n 400v capacitor loose in the box and it looks like a diode had gone up in smoke. Some of the traces have lifted. Has anybody got any photos of a working board or a schematic please? I have attached a photo of the affected area.

Yazoo55 · Post by **Yazoo55** » 13 Apr 2021, 16:40

I am still working on this. I rebuilt the burnt section and replaced the MOSFET, switched it on and got magic smoke again. It is basically sinking large amounts of current. I removed the MOSFET again and applied power - no magic smoke. I have not given up yet.

Another puzzle is that there are both LM7815 and LM7915 voltage regulators on the board, yet the power brick is DC. There are two diode bridges on the board. Any idea how you would get negative voltage when the power source is DC?

Yazoo55 · Post by **Yazoo55** » 17 May 2021, 01:08

I went around and around with this. In the end I was unable to get the high voltage section to work. Even after my rebuild and numerous tests, it still drew too much current. I got the pedal to work by using an NCH6100V nixie power supply and an LT1054 for the negative voltage. I had to heighten the case to fit these and 3D printed a case extender to do this. It is all working now. The plate voltage for the tube is slightly lower, 235v not 270v but it seems fine.