Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tcoil on June 10, 2010, 12:49:24 am

Title: Fender hot rod deville channel switching prob.
Post by: tcoil on June 10, 2010, 12:49:24 am

Hi fella's, Got a Hot rod Deville that won't stay in the channel  switch or more drive mode the light red or green turns on and off. especially if you tap on the top of amp. I thought it was the relays so I replaced them and it still drops out and the light goes out. Any one else seen this. Any suggestions would be greatly appreciated.

Thanks 

Title: Re: Fender hot rod deville channel switching prob.
Post by: navdave on June 10, 2010, 02:36:44 am

Might be loose solder joints in the switching power supply. I had a solid state crate amp that would do that to me a long time ago but that was before I started tearing in amps.

Title: Re: Fender hot rod deville channel switching prob.
Post by: LooseChange on June 10, 2010, 05:16:44 am

Right in the middle of the main board there are two white cement brick resistors... Check them, replace them. They cause most problems with the switching and solid state stuff in those amps.

Title: Re: Fender hot rod deville channel switching prob.
Post by: mageerc on June 10, 2010, 07:01:31 am

Quote from: LooseChange on June 10, 2010, 05:16:44 am

Right in the middle of the main board there are two white cement brick resistors... Check them, replace them. They cause most problems with the switching and solid state stuff in those amps.

When you check you might find that the board is discolored around these resistors from the heat these boogers put out.  When you replace them, float them above the board 1/4" or so with some silicone under them ans it will help with the heat problem...

Title: Re: Fender hot rod deville channel switching prob.
Post by: jjasilli on June 10, 2010, 11:07:12 am

I had this problem in my HRD.  Turned out there was !!!no solder!!! in the board where the 3 prongs of panel SW (Channel, changing SW) are mounted.  (I think it is also possible, due to a Rube Goldberg-like grounding scheme, that if the input jack connections to the board have gone bad, it can make the Ch SW become erratic.)

Title: Re: Fender hot rod deville channel switching prob.
Post by: tcoil on June 11, 2010, 01:37:38 am

Thanks for the suggestions I will replace the resistors.  I checked all the solder connections and they all look solid.

Title: Re: Fender hot rod deville channel switching prob.
Post by: tcoil on June 13, 2010, 07:28:39 pm

Here is an update re this amp switching problem. I have isolated the board from the chassis and the problem is gone. I have the cement resistors on order and will replace them even though they're specs are good. I have no Idea why it has a problem when the board is installed and bolted in to the chassis and it works fine when I unbolt it from the chassis and lay it in a rubber pad as not to short out the board. I have to suspect some kind of grounding problem. Looks like a needle in a hay stack. Any suggestions?
Thanks

Title: Re: Fender hot rod deville channel switching prob.
Post by: tcoil on June 13, 2010, 11:21:13 pm

update #2  Thanks for the replys, it turns out it was a ground problem. had a ground wire I forgot about that snuck under the board. It was just the relays after all.  :wink:

Thanks again fella's.