Hot Rod Deluxe III No Power

[dpm309]

I have a Hot Rod Deluxe III that has no power. Fuse and thermistor check out. I measured resistance between both primaries and got 5 Ohms. When I checked each to the chassis, I got an open reading on my voltmeter. I am suspecting that the PT is fried since even the pilot light does not come on. Any other tests I should try? I have attached a schematic for the Hot Rod Deluxe/Deville III.
Thanks

[John]

I guess just to be sure, I'd disconnect the secondary, throw the juice and see what they measure across them.

[shooter]

+1,
your fuse is still good, sacrifice it 

even the pilot light does not come on

most everyone that has fixed broke stuff long enough has got side-tracked because a light was bad.  Guessing yours is fine, just don't go running before you verify

[dpm309]

I am getting 450VDC at the first filter cap and 6.5VAC across the heater secondaries. I noticed that when I first turn the power switch, the pilot light flashes very faintly and then goes dim. Fuse f2 (connected to the heater secondaries near the power tubes) is not blown. Still no sign of the tube heaters lighting up. Pulled the power tubes, and the pilot light stayed on for about 1 second and then shut off. Then pulled the preamp tubes and the pilot light stays on. Will check out the tubes next. Could a shorted tube be causing this?

[shooter]

Still no sign of the tube heaters lighting up.

since all the tubes are out, probe the 6.3vac from tube side pin to ground, suspect you have a loose wire/ cracked solder joint,  the pilot lamp if it's part of the 6.3vac string.

[dpm309]

Thanks Shooter, will try that next.

[dpm309]

OK, I measured the heater voltage to ground on all sockets and pilot light and am getting 3.5VAC. Pulled the board and visually checked for cold solder joints/cracks and did not see any. Reinstalled the board and the tubes and they all lit up. Fired up the amp and it seems to be working just fine.  Wondering if something got knocked loose that somehow got fixed by removing and replacing the board. Go figure! I will run the amp for awhile to make sure everything is OK and report back if I have any more issues.Thanks for all your help.Dan

[jjasilli]

Pulled the board and visually checked for cold solder joints/cracks and did not see any.
I've got an HRD.  The truth is that every solder joint on the board is a cold joint.  IOW, the cold board is held above a pool of molten solder, and a wave of molten solder touches the cold joints.  These solder joints are liable to fail or go intermittent at any time.  There are no eyelets for security.  Also the board is thin & tends to flex, especially when taken in & out, which stresses all the solder joints.  The flat computer connectors are also prone to failure. 

Rather than pull the board, to make changes or repairs you may wish to consider making point-to-point connections on top of the board without pulling it out of the amp. 

[dpm309]

Yeah, Marshall uses the same process with the same problems. Ended up replacing the whole main circuit board in a Marshall DSL a couple of years ago. Been running the HRD for a couple of days with no problems. I am wondering if it was one of the heater connectors. Will continue to test it out over the next few days.

[dpm309]

Been running this amp for over a week now and the only issue I am left with is fairly noticeable hum on the clean channel. If I set the volume at about 3+/-, the hum virtually disappears. The owner bought this off of Craigslist as is so I have no way of knowing if the hum was there when it was working properly. Will try new preamp tubes to see if that solves it. Could this be related to the heater circuit issue? Have read various posts on other amp forums that this is a fairly common problem with the HDRs. My only other possible solution would be to pull the board and refloat all of the tube solder connections which would be a major PIA.

Dan