nevetslab 8/2/2018 10:02 PM
Fender pro reverb combo, nasty normal ch volume pot
In going thru all of our rental gear performing preventative maintenance on everything that hasn’t been serviced for 3 or more years, I came upon the first of the two Fender Pro Reverb Combo amps. Began with the amp on my check-out bench, with DMM probes poked into the Tube Bias Test Points to check out their plate current levels, that looked fine. I then moved the amp around facing the front, and begin giving a listen to the controls with no signal applied, seeing if there were any notable issues.

The Normal Ch Volume pot was downright scary! Loud scratchy noises with the slightest turn of that pot. Just exercising the pot was frightening. I went to S/B, then exercised the dickens out of the pot, finding that did nothing. So, I pulled the chassis out and moved it to sit atop my Marshall service cradle. I was not impressed with what I saw. Even after liberal spraying of Caig DeOxit 5 into the pot and exercising it, the pot was beyond cleaning that way.

Fender’s design team must have looked at some Mackie mixers and Peavey products, deciding to make use of the multitude of wire jumpers and resistors to span the gap between the main PCB and the front panel PCB. There is absolutely NO WAY to remove this front panel board, even if you could successfully unsolder every wire jumper and resistor without destroying the solder pads, and then get the PCB out. The vertical filter caps at the supply end says NO YOU CAN’T.


So, that leaves you with having to remove the main PCB together with the front panel PCB, as it seems that was how the boards were installed. More boards have to be removed first, and a number of transformer wires removed, etc. All of this just to get at a noisy pot???!!!!

My first impression was to write up the Estimate Invoice, pointing out this monumental task, and to find out just how much rental activity have these two amps gotten over the last 4 years? I left this chassis on the bench, moved the cabinet off and put the other amp up on the bench. It had EXACTLY the same problem as this one. AND, just like this amp, the volume pot would NOT quiet down with repeated exercising.

I came back to it a while later, now armed with my smaller Foredom hand grinder & carbide burr, to see what the access was like to reach in and cut the pot legs and support bracket tabs off of the PCB. Then, grabbed my Erem 71AE 45 deg flush cutting dikes, as well as the Erem 503E 45 deg flush cutting dikes, and saw they might be a more tame means to cutting the pot free. Then, I could remove the pot, unsolder the left-over terminal debris, install wires, and then install a new 1M Audio pot with the same 1/4” shaft detail. Not elegant, but seems like the only way to salvage this amp at this point in time.

Fender gets an F on making this amp serviceable!

Any other suggestions?
Randall 8/2/2018 11:15 PM
Two thoughts. First, this is not a Pro Reverb, no matter what the current owners say. Blasphemy!

Second, I realize I am in a different situation than you as I do not have a boss. But I would tell the customer what is involved and that unfortunately when your car costs more to repair than it's worth, everyone accepts that it is "totaled". IMHO, the same is true here. If it is going to take me extended time to correct a noisy pot, then I must be paid for it. I used to be charitable about that when it only happened once in a while, but as more and more gear is designed with no service plan considered, I now think it just isn't my fault or my problem. Will I fix it? Yes. But not for less than my rate because I feel bad that my customer bought a crap design.
Justin Thomas 8/2/2018 11:34 PM
Heck, I might consider cutting all thise jumpers, remove the pot board, then desolder all the jumper stubs from both once there's some room in there... Just add new jumpers when you're done, quick-solder them in place...

Just a thunk I had...

nevetslab 8/3/2018 12:13 AM
I'm only going by the what's on the front panel, it being one of the Pro Tube series Pro Reverb, looks like what's in the owner's manual. Obviously NOT one of the older Pro Reverb amps. This is one of the Deep Depth combo cabinets, single 12". It matches what's on our inventory list. Regardless, it's been in our inventory for at least a decade or more.

After discussing the tear-down approach to extracting the front panel PCB with our General Manager, and thought the only economic solution would be to cut the pot out from the PCB, and could get that operation done in less than a couple hours, he was willing to go that route.

BTW, I'm an independent contractor, not an employee of CenterStaging. I've just been handling their equipment maintenance on site since 2009, as well as other clients there at my shop. So, I don't really have a boss.
pdf64 8/3/2018 12:30 AM
The pot board canít be removed with the main board in place.
But it may be feasible just to remove the main board screws, slacken off the back panel fixings, angle the main board up, and slide the front panel back, underneath the main board. Then angle the pot shafts up and ease the pot board out.
Maybe some pillars for the main board would get in the way of sliding the front panel under it enough but perhaps they could be removed from under the chassis without too much trouble.
Enzo 8/3/2018 12:43 AM
Try giving Fender a call, and ask for service. I mean repair, not "customer service". Someone from CS will try to qualify you first - they don't want some kid calling their techs and yapping about 12AX7 brands for half an hour. But you should be able to get to service by describing your disassembly dilemma. Ask them how they do it. I used to talk to Jody when I needed support, but I don;t know if he is still there, and I have nothing against the rest of the staff.

I don't know if you do warranty work, in particular for Fender, but the way Fender does it, each technician has to apply and get a rating. Then a potential service center applies for warranty shop status, and identify the rated techs who will be on staff. If you only have two bronze level techs, your shop will not become a silver rated warranty shop. But having a Fender tech rating does not obligate you to do warranty work or even work in a shop that does. it is merely an acknowledgement from fender that you yourself have met certain standards. You would no doubt be accepted as a silver tech right off. I don't think they hand out gold until you have been in the system a while.

Forgetting the warranty work aspect, having that certificate affords you better access the the innards of Fender. It costs nothing, you take a tech test that is not difficult, and what can it hurt? My gold ticket is the only certificate I saved from my shop.
glebert 8/3/2018 9:25 AM
Quote Originally Posted by pdf64 View Post
The pot board canít be removed with the main board in place.
But it may be feasible just to remove the main board screws, slacken off the back panel fixings, angle the main board up, and slide the front panel back, underneath the main board. Then angle the pot shafts up and ease the pot board out.
Maybe some pillars for the main board would get in the way of sliding the front panel under it enough but perhaps they could be removed from under the chassis without too much trouble.
I was going to suggest similar. I find I have to do the "slide and flex" more than I would expect, and with a main board as big as that Fender it will be extra tight.

To nevetslab, I am impressed that 1.) you have two different flush cut 45 degree diagonal cutters, and 2.) you know their model numbers. Those must be some good tools.
nevetslab 8/3/2018 10:55 AM
Quote Originally Posted by Randall View Post
Two thoughts. First, this is not a Pro Reverb, no matter what the current owners say. Blasphemy!
You're absolutely right, with regards to the original Fender Pro Reverb. Even though Schematics for those label it Pro Reverb Amp, of which I have many in my Pro Reverb folder, this amp is from their Pro Tube Series, and just to confuse the public, they put this on the front panel:


Their schematic on this amp says nothing about a Pro Reverb Amp though. Just calls it Pro Tube Amps. Combo case is very similar to the Fender The Twin (Red Knob Twin) or the Twin Amp.

And, it bears no resemblance to the REAL Fender Pro Reverb amp inside and out!
nevetslab 8/3/2018 11:12 AM
I've actually never gone thru the steps to become a Factory approved/trained warranty tech. I've thought about that, but, logistically, it would no doubt move me out of the 33ft by 10ft x 12ft cluster of former closets that was given to me for doing the maintenance work at CenterStaging back in 2009. Didn't even have power in the room yet. In many ways, I've wanted to expand, which would put me into commercial space, with all the monthly expenses needing to be met on top of how I scratch out a living just getting by. As it is, I've been trading 20 hrs labor for shop space, and have no overhead here. When I get really busy, the road cases become a problem, and end up in the hallway that serves three of the rehearsal studios here at CenterStaging...their main business.

Something to think about for sure....Lord knows I need a whole lot more steady clients to get from just getting by monthly to actually being able to put $$ away, and pay quarterly taxes when due.

I think I will call Fender to see if there's anyone there who does have a clue just how they disembowel one of these to replace pots. I had already written up the post before our General Manager came to see me, and I discussed my after-thought of cutting the pot free from the PCB and retro-fitting a new one with wires. That got his approval, being minimal labor while getting it done professionally and fitting into their budget. If it was going to take more than 2 hrs, it would have moved the amp into the Sell It Off status. It may still land there in time, but as much as it bothers me hacking something out, it's the least painful approach.

All this came up from my doing preventative maintenance, digging thru all the popular brands gear in our inventory that haven't visited the shop for 3 or more years. Only 10% maybe of all the gear that's come in during this procedure hasn't needed any attention. The rest gets sent out on rental, unless the tech verifying what's going out finds something obvious. These two amps would have been one.
nevetslab 8/3/2018 11:29 AM
Erem 45 Deg Cutters
Being the tool freak that I am, I've always been a big fan of EREM hand tools. Only a few have I ever purchased thru distribution brand new. They're Oh-my-gosh expensive. But, from the years of having surplus stores accessible, and then ebay, I've come upon some really nice tools. Here's a few of their 45 deg Flush cutters:


The first one, the Erem 71AE was my first 45 deg cutter. Found it, and 3 like it at C & H Sales out in Pasadena in the late 70's, new in box, and paid $5 each for them. They are also the first tool I reach for when prying up the cover tabs of a potentiometer, when removing the cover for cleaning the pot resistive tracks. I even have one version of it that has an eleastic compound that fills the cavity of the jaws, used to prevent component leads from shooting across the room after soldering a part into the PCB.

The next one, the 582E is more like a ladie's production tool, having the soft grip, very similar to the 71AE. The 504E is a beauty, bigger cutter head, soft grip. The 119 is the smallest of the Erem 45 deg Flush cutters I have, and was the one that was able to reach in and nibble thru the pot terminals before I went home last night.
Enzo 8/3/2018 1:05 PM
Being certified as a tech shouldn't change anything in your shop. It is when your SHOP gets authorized that changes occur.

I don't worry about this Pro Reverb not being like the one from 50 years ago. Chevrolet has been making Impala models since 1957, The 2018 Impala has little resemblance to the 1957 version. it is just a model name, not a religious experience.
nevetslab 8/3/2018 1:11 PM
Pot removed, clean-up, extension wires added, new pot installed
The followup on the repair is shown in the next 3 photos:


I checked the results. The scary noises are gone, but....there's still some scratchiness as you rotate the pot. Cleaned the pot, 1M Audio, and NO DC on the source. At least it's now serviceable again. Yes, I mis-installed the Blk wire with the Yellow wire...intending Blk to be Ground. I get one more chance to get that right.