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Post subject: Hot Rod Deluxe - Channel Switching/Losing Reverb
Posted: Thu Feb 11, 2010 3:42 am
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hi all...

I have a very early Fender HR DLX. I used to gig a ton, and am now playing quite a lot again. BUT, my amp is having some issues and showing its age perhaps. I know this is an extremely common issue with these amps, but I can't find ANY info on the actual fix for it. I know there was a guy who came up with one [Justin Holton], but the info is no longer out there. Can someone PLEASE point me in the right direction? I have been having to use a crappy solid-state Fender amp, and it's killing my joy of playing! :) I have a show in a couple of weeks that I have to get this fixed for. Thanks in advance for any help you can provide!

take care... aaron d. garrett


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Posted: Fri Feb 12, 2010 10:37 pm
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I had the same prblem about two weeks ago. The problem that couses that are the power resistors used for the switching. In my amps case it was just a cold solder joint.


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Posted: Fri Feb 12, 2010 11:30 pm
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Thanks for the reply! I guess what I was asking us if anyone can tell me exactly where they are. I read what caused the problem, and I can replace them, but I need to know what part and where it is on the board. I had found a great diagram a while back, but the link is dead now. Thanks again.


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Posted: Sat Feb 13, 2010 7:53 am
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The 5 watt power resistors are R78 and R79 on the board. It's a real common problem with these amps. Mine spent almost as much time in the shop as it did on the stage so I got rid of it. Mine had this problem and many, many more. Mine got so hot it burned the board and lifted the traces. Cold solder joints on the tube sockets etc. are other problems.
Justin's site is gone. He did have a PDF file and if I can find it I'll post a link.


Here is something I found about it and it seems dead on. If you're experienced with amp repair, let a tech do it. There are potentially lethal voltages in there. I think this was from Justin's site.

"The 470 ohm 5W cement resistors in the +/- 16V supply are the cause of so many problems in the Hot Rod Deluxe/Deville it's unbelieveable. Are your channels randomly switching on you? Are you getting an uncontrollable squealing/feedback sound that appears after the amp's been on a while? Is the reverb dropping in and out?

The main problem is that the resistors get so hot that they form cold solder joints. Cold solder joints are caused by physically stressed leads that are subjected to vibration and repeated heating and cooling cycles. (They are very common on PCBs which use a wave soldering method like the Hot Rod Deluxe.) If your amp acts fine when you first turn it on, but after a few minutes starts showing the aformentioned symptoms, then you likely have one or two cold solder joints. These are characterized by a dry/dull appearance; a good solder joint will appear shiny and clean.

The DC voltage from the resistors power the channel switching relays, the effects loop opamps, and reverb opamps. Once the joints get hot they'll stop conducting for random periods of time. This is what causes the channels to switch and the reverb to drop out. The cold solder joints also cause your amp to "feedback" whether a guitar is plugged in or not—particularly the More Drive and Drive channels. I think this is actually some type of oscillation, but I don't know exactly why it's caused. Still, doing this procedure fixes the problem.

Another problem is how the resistors are prepped. Look at all the other resistors in your amp. The leads come straight out of the component, bend at a 90 degree angle somewhere on the lead, and then are soldered onto the PCB. The 5W resistor's leads are bent as soon as they come out of the body. You should never bend leads like this. This puts stress on the inside of the component and causes it to crack. Remember, some resistors could be burned up, cracked, and totally disfunctional and you'd never know from looking at the outside. The only way to test it is with a multimeter.

Now that you know why your amp's acting flaky, how can we fix it?

1. For a permanent fix you'll need to order a few parts. VintageJon, an extremely reliable tech at the FDP, wrote that Fender put out a bulletin recommending that these resistors be replaced with 330 ohm resistors of the same type—the old value was 470 ohms. Apparently Fender now uses 330 ohm resistors in newer amps to prevent this problem, but I haven't seem this implemented. Someone emailed me and said it was better to use a higher resistance rather than a low resistance, but I have not been able to confirm this yet. The disagreement is over how the resistor drops voltage. All the RadioShacks in my area do not carry any 5W resistors over 1Ω. Chances are yours won't either. It'd be good to call them first to save you the time and gas. The largest values I could find there were 10 ohms! Click here to buy better quality power resistors right off of Mouser. If you have trouble with link, then do a search from the main page. Its Part # is 280-CR5-470-RC.

2. Drain the power supply's filter caps! This is for your own safety. If you don't know how click here. Your life may depend on it!

3. If you've drained the filter caps, and I hope you did, the back panel should already be removed. Now remove the chicken head knobs, black screws, washers, nuts, etc. Whatever you have to do to get under the PCB. It's also a good idea to remove the green ground wire that's on the same side as the input jacks. This will make getting under the PCB easier. Be sure to store these parts safely so none are lost.

4. Look for the two problematic resistors (R78, R79). They are in at the bottom-center of the PCB. (They look like two white blocks, and are right next to the bias pot.) Now that you've found them on top, you'll need to find the location of their leads on the bottom of the PCB. This is essential if your fix is temporary or permanent.

5. (a) For a quick fix, "touch up" the solder joints by adding a little solder to all four joints. This will keep you problem free for awhile, but not for good. For a permanent fix: unsolder the two 470 ohm 5W resistors. You may need to clip the tips of any leads under the PCB—if they're bent in a hook shape. (Probably all of them.) If not, it'll make this step more difficult as they get hung up when you try to pull the resistors out. (b) Be sure to remove as much solder as possible with a solder sucking device. If not, you could damage the solder points which are just a thin piece of foil glued to the PCB. Then you'll find yourself running a lot of jumpers—like me. Also, it can get awkward trying to unsolder on one side and remove on the other. It's always nice if you can keep someone nearby to assist you.

6. Take the new 330 ohm resistors and bend the leads—but not right where they come out of the component. This is the proper way to "prep" a component. This will take stress off of the inside of the resistor, which will keep it from cracking and failing prematurely. (a) NOTE: The "prep" in the picture to the right is exaggerated for clarity. You don't need to bend your leads that far out, though you can if you want to. Just don't bend them right where they come out of the body. That's the most important thing to remember. (b) A good trick is to place a miniature screwdriver right against the body of the resistor and bend the lead around the screwdriver at a 90 degree angle. (c) This prep will be far closer to the body than you could get it with your fingers, and it will look more professional than any wildly prepped leads bent further out.

7. If you have some Silicon Rubber Sealer apply some under the resistor. Use it to prop the resistor up off of the PCB a little. This will help keep the resistor from vibrating when it's trying to dissipating heat, which in turn will prevent cold joints from reforming. Solder the resistors into place. NOTE: Be sure to give the silicon 24 hours to cure before turning on your Hot Rod. Once it has cured it will be completely inert to electrical current.

8. Screw everything (PCB, jacks, knobs) back into place. If you've done everything correctly you should be problem free for a long time.
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Post subject:
Posted: Sat Feb 13, 2010 9:54 pm
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The tech that did mine recomended that I keep the 470 resistors in it. He said that the voltage drop across the 330 resistors would put more stress on the power supply. He said if it did it again to upgrade the quality of the resistor but keep the same value.


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Posted: Sat Feb 13, 2010 10:13 pm
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I agree with your tech. Keep the original value. I would also mount the resistors slightly off the board for a little airflow. When they go, they sometimes burn the board and destroy the traces.

Never buy any components from Radio Shack. They pretty much sell garbage. Personally, I use Mouser.


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Posted: Sun Feb 14, 2010 1:54 am
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thanks so much. this is immensely helpful. i do believe i'll be taking this to a pro. as soon as i read the word "lethal," i figured i was out of my professional scope. the scary thing is that i actually spent a bunch of time a few years back looking through the guts... had it all apart and was handling it. scary! thanks so much for the help... really helpful!

adg


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Posted: Sun Feb 14, 2010 9:05 am
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I'm glad I mentioned the word "Lethal". I for one would like to be able to to see you post and try to help answer you questions. :wink:


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Posted: Sun Feb 14, 2010 7:10 pm
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This is so cool. I just got on here and already feel helpfull :D


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Post subject:
Posted: Mon Feb 15, 2010 12:24 pm
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I found a link to Juston Holton's Unofficial Hot Rod Deluxe Users Guide.
His site is down, but he is hosing a ZIP file. This is a must have if you own a HRD series amp. It has fixes and mods with lots of photos.
Here goes

http://www.zshare.net/download/717489209e4aa2e7/


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Post subject: Found! The Unofficial Fender Hot Rod Deluxe Owner's Guide!
Posted: Sat Sep 11, 2010 8:49 pm
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Found Justin Holton's Hot Rod Deluxe and Deville info. He doesn't support it anymore and does not want to be bothered with questions.

But . . . I found the unlinked old site by searching justinholton and hotrod which got me to:
http://www.justinholton.com/hotrod/

Most links work, some don't - like his email which is understandable.

I am simply amazed as to how organized and well written the site is/was.
Thank you Justin.


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