Ampeg V4 Standby Switch

[Pryde]

I have an Ampeg V4 with a standby switch that doesn't work. The light comes on/off but when flipping back to standby the amp just stays in operation. I put in a different switch but still the same issue so somewhere the wiring is off.

Schematic:
http://www.ampegv4.com/images/schema...VT-22_1977.jpg


The switch leads connect to the correct part of the board (negative side of bridge rectifier and other lead to D5). Not sure what gives?

Note: The amp has had filter caps replaced before with what appears to be some shoddy work so possibly something is not wired correctly? Hard to make good sense of all the series/parallel cap wiring in the filter section.

Thanks for any advice.

[Pryde]

Looking at this further I found an image of the rectifier layout on the pcb. The circled area is the negative side of the rectifier where one lead of the standby switch goes. To the left of that the other standby lead hooks to the D5 cathode. which I believe is correct.

However, in standby mode the main filter caps are still grounded which I believe the ground should be lifted in standby correct?
This is a different type of standby I am not familiar with so any wiring advice would be appreciated.

[g1]

May be the wiring at the "new" filter caps. The cap shown as C18 may have been grounded, it's not supposed to be. It's negative end should only go to the point you have circled. It should get it's ground reference via the switch and D5.
Not sure if that would explain the light still working though?

[52 Bill]

Looking at this further I found an image of the rectifier layout on the pcb. The circled area is the negative side of the rectifier where one lead of the standby switch goes. To the left of that the other standby lead hooks to the D5 cathode. which I believe is correct.

However, in standby mode the main filter caps are still grounded which I believe the ground should be lifted in standby correct?
This is a different type of standby I am not familiar with so any wiring advice would be appreciated.

The standby switch disconnects the power supply from the amp after the first set of filter caps for the A and B nodes. If the switch was in the positive voltage leg of the supply, it would be just like the standard Fender standby circuit.

My guess would be that the filter caps for the C-D-E nodes of the power supply have been grounded to the wrong side of the standby switch circuit.

[Pryde]

Yes both can caps are grounded (C18 and C20). Weirdly they are both 50/50 caps where the schematic calls for 40/100 cans.

Then after that the can caps connect to ground and the (-) of the flying pair of 47uf caps in series? At that ground junction/turret, the tan wire connects up to the negative side of the rectifier on the pcb (where one of the standby switch leads also connects. Baffled

[g1]

At that ground junction/turret, the tan wire connects up to the negative side of the rectifier on the pcb (where one of the standby switch leads also connects. Baffled

At that ground junction/turret, the tan wire connects up to the negative side of the rectifier on the pcb (where one of the standby switch leads also connects. Baffled

At that terminal strip, disconnect from ground. So you will have the black from the can, the brown from the board, and the lead from the black cap all connected together, but no connection to the terminal that is chassis grounded.

You don't need to bother about the cap values, the series-parallel combinations work out to be almost the same.

[Pryde]

Thank you g-one. That took care of it. Funny I did move those to another terminal before with no difference but revisiting it using your advice I noticed a small jumper from the middle terminal connected to the one I used.

Had some other grounding issues elsewhere on the circuit that also were fixed. All appears to be functioning well at the moment.