Frustrating Problem With Fender Hot Rod Deluxe PR-246

[xtian]

Yes, tubes installed, normal operation. Best to have a dummy load so you're not driven mad by high volume 1KHz tone! Really, a scope is required for this process. This one is great, and inexpensive: https://www.amazon.com/FNIRSI-1013D-Plu ... 0BHHYMVKV/

[Scottyman]

Yes, tubes installed, normal operation. Best to have a dummy load so you're not driven mad by high volume 1KHz tone! Really, a scope is required for this process. This one is great, and inexpensive: https://www.amazon.com/FNIRSI-1013D-Plu ... 0BHHYMVKV/

Yeah, I can pick that up in the next week or so but I've never used one.
I'm guessing there's a bit of a learning curve on something like that.

[Scottyman]

Yes, tubes installed, normal operation. Best to have a dummy load so you're not driven mad by high volume 1KHz tone!

Can you use an inexpensive $20 dummy load resistor that you can find all over ebay? I think they have one rated for 200 watts.

[Scottyman]

Since its so cheap and can be done fast on the parts side of the board ( by cutting them out and tacking on new ones) I would replace both of the PI tubes plate load resistors.

I have had them go bad many times yet they look good.
Use 1 watt resistors or two half watters of the needed value in parallel or series.

So, according to the video, there are 4 plate load resistors, R4, R11, R16 and R22. He suggests replacing all of them with Vishay Metal Film resistors. Is that something you would do? Mine are all reading 100k resistance and look good but I want to make sure I do everything right. So your suggestions are all helpful.

Also, up on the top left of the board on the power section, there is a 1,100 ohm resistor and there is evidence of heat damage starting to occur at the terminals. The slot number is R97 and it looks like a normal carbon film resistor. I'm thinking I should replace that as well with something better but I wanted your thoughts on that as well.

And I'm starting to wonder if that resistor might be a problem. According to the chart, it should be 1200 ohms and not 1100 ohms. Can someone clarify this for me? It's really hard to tell. It looks like it could be brown brown brown or brown red red. I think the picture is a little easier to see then my eyes.

Note: OK, I found it in the diagram. It's a 1.2k ohm 2 watt.

Is it OK to replace it with something like this?
https://www.mouser.com/ProductDetail/Vi ... H7iWbKg%3D

Thanks!

[nuke]

That looks like a MOX (metal oxide) resistor. They usually use these in places that get hot, and are sometimes also called, 'flameproof' resistors. They'll open up in overload conditions without much smoke and no flame.

Usually metal films are kinda glossy and often use the 4 band color codes, and are frequently blue in color. Carbon film is usually a light tan in color. Metal oxides resistors are usually matte looking with a rough surface and are often green, or grey or sometimes pink.

For power supply resistors, I like to use MOX, just in case something shorts out up to about 2 watts and wire wound for anything dissipating any more than that.

For plate load resistors, I like 2-watt carbon films, since they're rated for more than 500v. Metal film can be quieter, but have to look at the voltage ratings, which are sometimes lower than we might like. Film resistors are constructed by a spiral of resistance material on a ceramic core. The voltage considers both the voltage between the terminals, and the insulation resistance of the coating on the outside of the resistor.

I've seen numerous Blues/HotRod Deluxe/Devilles with crapped out effect loop jacks. Second most likely issues are the electrolytic caps, overheated parts/board and cracked lead-free solder joints.

Brad's video treatise on the Fender Hot Rods is pretty thorough and spot on. I see way more Blues Juniors where I live.

They're both built like crap, and another $20 spent on the BOM would make them great and reliable. I just yank the boards out after some basic diagnostics to sort out the complaint and then take care of all the dumb stuff that has or will go bad.

Fender also use the worst lead-free solder I've encountered. One pro-tip for working on them is get yourself a spool of good quality lead-free solder, some high-quality solder wick, some Chip-Quick flux and a spool of 63/37 leaded solder.

Touch-up lead-free with a little dab of flux and lead-free solder. Don't mix leaded and lead-free solder together. If you replace a component clean up the lead-free with solder-wick and flux, then solder the replacement part in.

The boards are crap too. It is preferable to snip the leads off the component, then pull it out the solder side with tweezers. The leads are folded over the solder pad by the insertion machine and trying to desolder them and lift the lead off the pad will just destroy the copper pad.

Always clean the board when you're done too. High voltage and flux residue are not good friends.

[Scottyman]

That looks like a MOX (metal oxide) resistor. They usually use these in places that get hot, and are sometimes also called, 'flameproof' resistors. They'll open up in overload conditions without much smoke and no flame.

Usually metal films are kinda glossy and often use the 4 band color codes, and are frequently blue in color. Carbon film is usually a light tan in color. Metal oxides resistors are usually matte looking with a rough surface and are often green, or grey or sometimes pink.

For power supply resistors, I like to use MOX, just in case something shorts out up to about 2 watts and wire wound for anything dissipating any more than that.

In the video the guy explains that you can use a slightly higher wattage one in place of the original and that helps keep it a little cooler. As long as I replace it with a 1.2k resistor and it's a MOX, can I put in a 3 watt one?

Or if not that, what would be a good replacement in your opinion?

[sluckey]

I would use a 3 watt and also mount the resistor about 1/2" to 3/4" above the board to avoid heat damage to the board.

[nuke]

Yeah, exactly what sluckey says.

You can go up in watts until it gets difficult to fit it on the board. Put a little c-shape kink in the leads so it stands off the board a bit and allows the heat to dissipate before it reaches the board.

[Scottyman]

Yeah, exactly what sluckey says.

You can go up in watts until it gets difficult to fit it on the board. Put a little c-shape kink in the leads so it stands off the board a bit and allows the heat to dissipate before it reaches the board.

Fantastic.

I ordered all the parts listed in the video and some extra stuff to make sure I get it right.

Thanks for the advise guys!

[chaccmgr]

Hi,

I might be a bit late to this discussion. I had some different Hot Rods on the bench some time ago, and they all share similar problems ("Hot Rod Disease").
Here you find a collection of common problems together with solutions. Your problem is listed too:
http://hotroddiy.com/
http://hotroddiy.com/Problem-Solved!.pdf

BR

[martin manning]

Just for grins I did a Google search on "what are common failures in Fender hot rod deluxe pr-246" and let the AI make a list. It's pretty good, and I expected as much since they are so frequently discussed on the web.

[nuke]

Yeah, Fender sold eleventy-bazillion Blues/HotRod Deluxe/Deville amps over the last 3 decades. Probably just as many Blues Juniors as well. No surprise that ChatGPT ingested a ton of internet messages about them.

I haven't had a deville/deluxe on the bench on a long while, but have had a bunch of Blues Jr's come through. On the juniors, ignore the advice about pulling the main board and leaving the tube board in place. Just take them both out all at once, after you figure out what you need to fix. Far less damage to the ribbon cables and honestly, it makes the repair work a lot easier an faster.

They're both made of let's call it, the "left side of the quality curve" parts.

[Scottyman]

Hi,

I might be a bit late to this discussion. I had some different Hot Rods on the bench some time ago, and they all share similar problems ("Hot Rod Disease").
Here you find a collection of common problems together with solutions. Your problem is listed too:
http://hotroddiy.com/
http://hotroddiy.com/Problem-Solved!.pdf

BR

Thank you. I'll read it over this afternoon. I'm still waiting on the parts I ordered but should have them by Friday.

[Scottyman]

For plate load resistors, I like 2-watt carbon films, since they're rated for more than 500v. Metal film can be quieter, but have to look at the voltage ratings, which are sometimes lower than we might like. Film resistors are constructed by a spiral of resistance material on a ceramic core. The voltage considers both the voltage between the terminals, and the insulation resistance of the coating on the outside of the resistor.

I have a question for you since you seem to know this pretty well. I know that they modified these amps several times over their production, and my schematic might not be the exact correct one, but I'm getting weird readings off of the resistors. I decided to check all of them and on some of them they're all over the map. Most of them read OK though. For example, R1 and R2 are part of that mid production mod and they both read 33k. But R3 should be 1M but it reads .4. And I know that all of the brown/black/yellow ones should read 100k but a bunch of them are wrong. I have also noticed that per the diagram some of the resistors are different than on the diagram like R44 says 100k in the diagram but the color bands say 56k.

I am testing the resistors right at the wire close to the ceramic barrel. I was told years ago that the rest of the circuit can affect readings but I thought if you went right at the wires it would be the correct reading.

Am I wrong about that?
Or should these resistors be replaced?

I'm including my PDF of the testing and I'm still waiting on a couple parts and the tool.
But they should be here on Monday.

Thanks!

[Scottyman]

Never mind, I'm a dope!
Path of least resistance, first thing they teach in electrical repair.
The signal is feeding back through the board and giving me false readings.

One of the screen grid resistors is bad though and shows signs of overheating.
It should be 470 ohms and it's reading closer to 1000 and got so hot that it's discolored the color bands.
So I'm betting between that and the other stuff he posted in the video, that this stuff will take care of it hopefully.