Bogner Shiva blown flyback diode

[Zouto]

I mean the small orange colored trimpot on the separate heater supply pcb, not the bigger bias pot on main board.

[vintagekiki]

Orange colored trimpot is probably in switched power supply, do not adjust without schematic.
https://www.rsdsound.co.uk/product/replacement-tube-heater-supply-smps-for-bogner-shiva/

[Zouto]

Orange colored trimpot is probably in switched power supply, do not adjust without schematic.
https://www.rsdsound.co.uk/product/replacement-tube-heater-supply-smps-for-bogner-shiva/

So it would be good to have the right schematic or some instruction for setting that trimpot,test points, Voltages etc. I‘m not quite sure whether the actual setting of the pot is ok.

[vintagekiki]

So it would be good to have the right schematic or some instruction for setting that trimpot,test points, Voltages etc. I‘m not quite sure whether the actual setting of the pot is ok.

https://www.rsdsound.co.uk/product/replacement-tube-heater-supply-smps-for-bogner-shiva/#tab-description

[Zouto]

So I have to set the trimpot to get 12.6Volts DC on the 12AX7s heaters?

[vintagekiki]

Before adjusting 12.6VDC, measure the real heater voltage between pin4 and pin5, tube V1 and V4 ( 12AX7).

https://www.rig-talk.com/forum/threads/obnoxious-hum-on-bogner-shiva-20th-anniversary-head.178796/
^{Obnoxious hum on Bogner Shiva 20th Anniversary head}

[Jon Snell]

I don't think anyone has read the data sheet on heater voltage tollerances. The manufacturers state 10% + or -.
So if the voltage is 11.5volts, that is within tollerance, so no need to play with it.

[vintagekiki]

That's right, voltage tollerances is +/- 10%
Do not adjust the trimpot unnecessarily.

[Jon Snell]

Yes. Good comment Enzo.
If measure in circuit it will read about 250 Ohms both ways, making the less experienced amongst us believe it is faulty.

[Zouto]

That's right, voltage tollerances is +/- 10%
Do not adjust the trimpot unnecessarily.

I got 11.98 Volts, so no adjustment needed. Big THANKS for great support
Zouto

[Zouto]

Yes. Good comment Enzo.
If measure in circuit it will read about 250 Ohms both ways, making the less experienced amongst us believe it is faulty.

Well, measured both ways it read 2.2 Ohms, it was definitely shorted.

[vintagekiki]

Well, measured both ways it read 2.2 Ohms, it was definitely shorted.

Did you measure in both directions 2.2 Ohms, with or without a parallel connected flyback diode.
If with the relay winding, connected parallel flyback diode, remove it and measure the resistance of the relay winding itself.
May be a diode damaged (in short circuit) and you have incorrect results.

[Zouto]

Did you measure in both directions 2.2 Ohms, with or without a parallel connected flyback diode.
If with the relay winding, connected parallel flyback diode, remove it and measure the resistance of the relay winding itself.
May be a diode damaged (in short circuit) and you have incorrect results.

I removed D3 diode, it was shorted, measured 2.2 Ohms both directions, replaced it with an UF4007 diode, checked heater Voltages on V1 and 4, biased the amp after 2 hours warming up and now it‘s running fine and sounds great in all modes. The relay RE3 is ok, I really don’t know why the diode shorted out.