Ad Widget
Collapse
Announcement
Collapse
No announcement yet.
Hot Rod DeVille Burnt PCB
Collapse
X
-
Ok, so that's arcing between screen grid resistor and flyback diode. There was probably contamination of the board and/or the amp was run without a load.
There can be more than B+ between those two nodes, so a simple multimeter check for resistance between the two pads is insufficient, you really need at least a megger/insulation resistance meter at 1kV or higher to be sure that there's no longer dielectric breakdown between the pads.Such tests should be done with the output transformer disconnected from circuit.
I would probably completely excise the burnt PCB to virgin FR4, apply corona dope or similar, cut the traces to the diode pads to isolate it, and relocate the diode itself to the tube socket to be sure of the repair.
- Likes 2
Comment
-
Is this one of the newer ones?
Last week I had a Hot Rod Deluxe III with a pc board short between the left output tube bias feed and the plate lead.
No visual contamination or evidence of anything that could have caused the short.
Comment
-
This is the schematic. Fender_hotrod_deville.pdf
The arc was between CR5 & R62. I also found that R65 was open.
Comment
-
FWIW: I've seen these types of burns when there are screws, nuts, or other conductive items rolling around in the chassis. So, give the amp a good visual inspection and a shake to make sure nothing falls out or is still inside the amp."I took a photo of my ohm meter... It didn't help." Enzo 8/20/22
Comment
-
That's just a touch weak, enough to limit the available bias range. Proper -54V there would allow you to bias cooler.
Do you have -74V at the negative end of C43? What is your line voltage coming into the amp?
(also check that no one has altered R77 value)Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
Comment
Comment