Fender Hotrod Deluxe 2017

[m1989jmp]

Hi,

I've received the amp in the title with complaints of volume dropping in and out when played loud. Light tapping on the chassis started producing some weird howling noise, so I figured I'd replace power tubes, bias and go from there.

Set it around 50mA per schematic and started gradually increasing volume. At one point the tubes flashed blue really hard and the amp reverted back to humming.

Before I go about checking all the usual stuff I'm wondering about this blue flash, as I'm thinking it would be indicative of a problem.

Thanks all.

https://www.thetubestore.com/lib/the...-Schematic.pdf

Edit: I'll add that humming is not affected by any of the controls.

[xtian]

You've got some kind of intermittent connection to find--could be bad solder joint on ribbon cables, bad PI plate or grid leak resistor connections, power tube screen/grid resistors, etc. If, as you say, master volume does not affect the issue, then it's AFTER the MV in the schematic.

[SoulFetish]

Hi,

I've received the amp in the title with complaints of volume dropping in and out when played loud. Light tapping on the chassis started producing some weird howling noise, so I figured I'd replace power tubes, bias and go from there.

Set it around 50mA per schematic and started gradually increasing volume. At one point the tubes flashed blue really hard and the amp reverted back to humming.

Before I go about checking all the usual stuff I'm wondering about this blue flash, as I'm thinking it would be indicative of a problem.

Thanks all.

https://www.thetubestore.com/lib/the...-Schematic.pdf

Edit: I'll add that humming is not affected by any of the controls.

did you pull the output tubes and insert some bench tubes to eliminate them as the cause?

[m1989jmp]

did you pull the output tubes and insert some bench tubes to eliminate them as the cause?

I did, but only power tubes. It's evident to me now that buzzing starts (and blue light intensifies) when I tap around PI tube socket, as xtian suggested.

I'll pull out PCBs later on and see if anything looks strange. I do see PI resistors, sockets, ribbon cables, jacks etc. mentioned a lot when I google issues related to this amp.

Thanks for the answers.

[SoulFetish]

I did, but only power tubes. It's evident to me now that buzzing starts (and blue light intensifies) when I tap around PI tube socket, as xtian suggested.

I'll pull out PCBs later on and see if anything looks strange. I do see PI resistors, sockets, ribbon cables, jacks etc. mentioned a lot when I google issues related to this amp.

Thanks for the answers.

Pull the PI and see if the noise goes away.

[m1989jmp]

Yup, it goes away with PI tube removed while tapping around like before.

I'm wondering if I should just remove the whole PCB that contains sockets and rework the whole thing including replacement of those (as I've read) under-rated PI plate resistors?

[m1989jmp]

Another silly question that I can't find an answer to: when reflowing these PCBs, should I remove all previous solder or just reflow and add some more? When I don't remove old stuff, soldered contact gets a whitish coating all over it.

Reflowing all power and PI tube sockets helped a lot; the amp now starts to crackle at high volume only when playing certain notes, so it's back to the bench.

[Tone Meister]

If I have to get deep enough into one that I pull the tube PCB, then I use a desoldering gun and remove all old solder on all tube sockets and then solder all connections as new. On the earlier revisions of these amps, the R57 (82K) and R58 (100K) PI plate resistors would fail, but the newer ones shouldn't have this issue. I use 1 watt metal films there, which is overkill.

Also, another thing to check are the 1.5K at R64, R65 and the 470R at R61, R62 on the tube PCB.

You can check the pins on the tube sockets to be sure they're tight also. Also, clean the POWER AMP IN jack on the top panel.

[SoulFetish]

O

Another silly question that I can't find an answer to: when reflowing these PCBs, should I remove all previous solder or just reflow and add some more? When I don't remove old stuff, soldered contact gets a whitish coating all over it.

Reflowing all power and PI tube sockets helped a lot; the amp now starts to crackle at high volume only when playing certain notes, so it's back to the bench.

Yes, remove the old solder. The lead free solder used in these does not mix well at all with typical 60/40 solder. But I usually don’t have to remove these boards. Have you read voltages at all the pins of the pi to see if you can identify the fault?

[m1989jmp]

O

Yes, remove the old solder. The lead free solder used in these does not mix well at all with typical 60/40 solder. But I usually don’t have to remove these boards. Have you read voltages at all the pins of the pi to see if you can identify the fault?

I didn't even bother tapping on preamp tubes, PI is for sure faulty as crackling starts even with light tapping.

Now it's fine even when I bang on it pretty hard. I'll see if the customer wants to proceed with these upgrades, I'd rather skip the part when I have to pull one of these boards out, but nevertheless would like to make this amp a bit more robust.

Thanks again for the replies.

[Tone Meister]

Just take the black screws from the tube sockets and the tube PCB will fold out. Just be gentle. These are standard procedures with these amps, Devilles included.

[glebert]

I'm wondering if I should just remove the whole PCB that contains sockets and rework the whole thing including replacement of those (as I've read) under-rated PI plate resistors?

I think the defective PI resistors were only on the first run of these. This design is over 20 years old now, hopefully they have worked out the design flaws by now. All three of my Hot Rod amps have been the US made ones from about 96-97 and were bought as fixers.

[m1989jmp]

I think the defective PI resistors were only on the first run of these. This design is over 20 years old now, hopefully they have worked out the design flaws by now. All three of my Hot Rod amps have been the US made ones from about 96-97 and were bought as fixers.

Well, I was under impression that footswitch power supply dropping resistors (R78 R79) create problems on new models too.

The only other issue I'm having is buzzing/whistling from areas as shown on the pictures. I've used some kind of a plastic tube to pinpoint the locations, and for sure the sound is loudest at these 2 locations. It's not super loud, but I'm wondering if it's a sign of failing filter caps, as I've read these IC caps tend to fail/leak too.

Thanks for the answers.

[Randall]

The IC caps are a source of many mysterious problems.

[nevetslab]

I'd rather skip the part when I have to pull one of these boards out, but nevertheless would like to make this amp a bit more robust.

Whenever I'm servicing one of these, I always remove the main PCB, which also allows re-dressing the power xfmr secondary wiring from the multitude of ways Fender factory people throw them together. Invariably, with the main PCB dropped down for inspection on the foil side, I find fractured solder joints on the panel control terminals, input jack terminals, foot switch and Preamp Out/Power Amp Input jacks, as well as joints on the ribbon cables, power supply filter caps, and the bipolar supply circuit components...the 5W bathtub resistors & the 16V/5W zeners. The resistors tend to scorch the board, with the heat crystallizing the solder joints, as well as the leads/joints on those zeners. On some of the boards, Fender has changed the solder mask to allow just a tiny little spot of solder to hold the filter caps, while the foil pattern is a good 0.125" or 0.15" dia. 0.080" exposed tinned copper for those is a joke!

Also, after removing that main board, you need to tighten up the chassis standoffs, as they are invariably loose! I know it's a PITA to drop that board out, as mechanically, it just doesn't want to clear the pot shafts, as the opposite edge of the PCB gets held up by the xfmr lead bundles exiting the xfmrs. Very rarely do I NOT find issues on any of these boards, once dropped out. Not unless it's one of the couple dozen I have in our rental inventory, having gone thru and set them all up over the recent years.

And, as stated a couple times....de-solder, then re-solder suspect solder joints when you find radial solder fractures.