King Nothing No Effect Signal

[joelorigo]

Hello all, I am getting bypass signal, but nothing when activated, including no LED. I saw a previous thread with the same problem so I have already followed some of the advice there. One thing to note is that I socketed C3 & C4 to experiment later with the bass response that was discussed in an earlier thread.

First, these continuity tests are all good. (I should note that the LED comes on D&E, normal?)
3PDT switch pins:
Pedal bypassed:

• 1 -> 2
• 4 -> 5
• 7 -> 8

Pedal active:

• 3 -> 2
• 6 -> 5
• 9 -> 8

Looking at the top row where it connects to the main PCB:
Pedal bypassed:

• A -> F
• B -> C
• No continuity on other top pins

Pedal active:

• A -> B
• C -> D
• E -> F

Pins C is ground and D is the LED cathode connection, and they correspond to switch pins 5 and 6 respectively.
Pin A is the input jack and F is the output jack. Pin B is the effect input.


Then, these voltage tests (using a 1.7A Godlyke Powerall 9v adaptor):
V+ pad, should be close to 9VDC (typically lower due to diode drop, but will depend on your power supply) - I get 9.17

cathode pad of D2. This is the high voltage rail, it should be 230VDC or so - I get 0, so obviously a problem there!

I am including a photo of the section of the DMM to make sure I was using the correct section.

Oh, actually the first thing I tried was a different tube.

 

[joelorigo]

Here are a few. Q1 is a J201 that ti got from either GuitarPCB or Stompbox Parts.

Everything look ok here? What did you want to verify in this area?

 

[vigilante398]

Everything look ok here? What did you want to verify in this area?

Looks okay up close, on one of the other photos it looked like there may have been a solder bridge, but now I think it may have just been a glare from the lighting.

 

[joelorigo]

Looks okay up close, on one of the other photos it looked like there may have been a solder bridge, but now I think it may have just been a glare from the lighting.

I'll look closely to verify if you point out where that is.

What do you think I should do next?

 

[vigilante398]

I mean if you're still getting 0V on the cathode of the UF4007 we know we still have a problem with the SMPS. The circuit is not going to work until you get the high voltage rail sorted. Nothing is jumping out at me visually, but there has to be something somewhere going wrong. This could be a bad solder joint in the SMPS, it could be a short on the tube daughter board that's pulling the rail down, it's hard to say from the other side of a screen.

 

[joelorigo]

Just to be clear, SMPS = Switch Mode Power Supply, right?

And the SMPS is the whole Power Supply parts of the circuit?

 

[vigilante398]

Just to be clear, SMPS = Switch Mode Power Supply, right?

And the SMPS is the whole Power Supply parts of the circuit?

Yup, that's correct.

 

[joelorigo]

I got 9.14 volts at the V+ pad and 0 at D2. Can you measure voltage readings from point to point, an equivalent to tracing the audio signal with a probe, to pinpoint where the issue is?

 

[vigilante398]

I got 9.14 volts at the V+ pad and 0 at D2. Can you measure voltage readings from point to point, an equivalent to tracing the audio signal with a probe, to pinpoint where the issue is?

Is that on the cathode (end with the stripe) of D2?

You can trace power like that, but it's trickier with an SMPS because it's basically AC until it gets to the cathode of D2. So if your multimeter has an AC setting (or if you have an oscilloscope) you can check the anode end of D2 and see what's coming into it. The purpose of D2 in the SMPS is as a rectifier, converting the AC voltage from the FET into DC voltage. It needs to be an ultra-fast rectifier because the AC coming from the FET is significantly faster than 60Hz, and a generic rectifier diode like a 1N4007 can't keep up.

If you're not getting anything there, you can probe the gate of the MOSFET (connected to pin 3 of the NE555) to make sure the MOSFET is being switched. You should be seeing AC voltage there as well, but at a much lower level.

 

[joelorigo]

Is that on the cathode (end with the stripe) of D2?

Yes that is where I was getting the 0 reading

You can trace power like that, but it's trickier with an SMPS because it's basically AC until it gets to the cathode of D2. So if your multimeter has an AC setting (or if you have an oscilloscope) you can check the anode end of D2 and see what's coming into it.

I haven't ever used it yet, but it looks like it does!

The purpose of D2 in the SMPS is as a rectifier, converting the AC voltage from the FET into DC voltage. It needs to be an ultra-fast rectifier because the AC coming from the FET is significantly faster than 60Hz, and a generic rectifier diode like a 1N4007 can't keep up.
If you're not getting anything there, you can probe the gate of the MOSFET (connected to pin 3 of the NE555) to make sure the MOSFET is being switched. You should be seeing AC voltage there as well, but at a much lower level.

OK
Thank you!