VFE DragonHound and VFE SB V3 - Always In Bypass [SOLVED]

[Cybercow]

Did up my first VFE DragonHound with a VFE SB V3 switching board and find that it's ALWAYS in bypass. I pre-measured EVERY component before soldering it into place, so I know the values are all correct.

I know the switching board is working (except I've yet to verify the TQ2-L-5V relay) because the LED indicates whether or not it is bypass or engaged - AND - the dual-mode momentary-on option (tap-tap-hold) works inactivating or deactivating the dual-mode option.

With the unit powered up and engaged or in bypass, the input and output jacks are always shorted together.

I suspect the TQ2-L-5V. But I got them from Mouser. So the reliability of a known good relay is high. I have 9.2v at the SB V3 supply input with ~-4.5v and ~+5v at the - and + points between the two boards.

Any leads, options or something I may have missed?

[Cybercow]

I think I just solved it. In the SB V3 build doc, I completely overlooked the section regarding the "In the Choral Reef the following exceptions are applied" - where it says R5 & R6 are ONLY used in the "Choral Reef". As I wasn't building a Choral Reef" I ignore that bit.

Goona clip 'em out and see how it behaves. Results to follow . . . .

[Bio77]

It might be Q2.  That one cuts the output of the effect during switching, if it isn't working, maybe it is cutting always??

[Cybercow]

Bio77 - that shouldn't affect the state of the relay tho. The input and output jacks are ALWAYS shorted together, regardless of the state of Q2. I suspect the relay is misbehaving for one reason or another.

Q2 should be working. At least it tested good in my Peak Atlas DCA75.

The voltages are definitely off. I should (according to the DragonHound and SB 3V build docs) have -4.5v on the negative point and +9v on the positive points between the two PCBs. I only have ~+5.2 volts on the positive rail between PCBs. And the DragonHound board does not have +9v anywhere.

Still poking around.

[Aentons]

V+ should be +9V
GND should be 0V
V- should be -9V

The LP2950 puts out +5V

[Aentons]

Here is another measurement you could take to help track it down.

From the SB build doc:
(Pin7 of the PIC is 0v in effect mode, 5v in bypass mode)

However, It sounds to me like you may have a stuck relay

[gordo]

I've had issues with the 2950 that sound like your symptoms.

[Cybercow]

Here is another measurement you could take to help track it down.

From the SB build doc:
(Pin7 of the PIC is 0v in effect mode, 5v in bypass mode)

However, It sounds to me like you may have a stuck relay

Thanks. I'll check that out.

[Cybercow]

I've had issues with the 2950 that sound like your symptoms.

I'm using the BOM alternate: LM78L05 in place of the 2950.

Still poking' around . . . .

[Cybercow]

Ha! A bad Zener at D2 on SB V3 switching board. I noticed how the chargepump wasn't getting +9v at all - only +5.1v

I pulled the zener and checked the number - 1N4743 - meaning it should have been a 13v Zener. When I checked my stock, I noticed how I had some from Tayda and some from Mouser. So I took one from the Mouser tape and plopped it into D2 and voila! Instant fix. I threw out the 1N4743 diodes from Tayda.

Problem now solved. Thanks and hats off to those who tossed in their 2¢

[gordo]

Excellent.  Especially considering what a pig those relays are to unsolder...