Fender HRD IV -16 volt supply reading -10

[JMMP]

Have this on the bench, replaced r78 and r79 (470),
CR13 and CR14, C40 and C41, to no avail. Drive more drive led stays red in drive and more drive, no green in clean. Heard if the led fails it won't switch, anyone wanna chime in? Thanks in advance

[Helmholtz]

Check CR14.
Do you get -48V before R79?

[JMMP]

Yes I replaced both zeners, and I do get 48 volts at r79.

[Helmholtz]

Is C41 good?
Was the replaced R79 good?

[JMMP]

Is C41 good?
Was the replaced R79 good?

Yes, replaced C41, and R79 was good.

[g1]

Are any of the IC's getting hot?

[JMMP]

None getting warm to the touch

[Mick Bailey]

Heard if the led fails it won't switch, anyone wanna chime in? Thanks in advance

The switching is done using opamps configured as comparators - an imbalance in supply rails screws this up and hence the switching doesn't operate correctly. Assuming no component issues in the PSU itself, then the voltage drop is most likely down to either high series resistance somewhere or excessive current draw. If excessive current draw, I would expect something to be getting hot, but as nothing is, then maybe there's some resistance in the circuit. You could do some point to point resistance checks to make sure there's continuity between components in the PSU.

[Delta362]

Check D17 and D22 (5.1V zeners), plus Q3 (2n4403) and Q4 (2n4401) and C45 (22uF cap).

[Delta362]

This schematic will be much closer to what you have

[JMMP]

Check D17 and D22 (5.1V zeners), plus Q3 (2n4403) and Q4 (2n4401) and C45 (22uF cap).

Can't find C45 on the schematic

[Delta362]

Can't find C45 on the schematic

It's just to the left of the Red/Green LED on sheet 1

[JMMP]

Ah, there it is, thank you!