Clean Your Dirty, Filthy, Disgusting Circuit boards.

eolon

Gold Supporting Member
Messages
509
Fender circuit eyelet boards can become conductive when they get dirty, and create mysterious and annoying noises. Sometimes the contamination is bad enough to create arcing across high voltage solder points and cause components to fail. The only way I have found to completely eliminate this is to thoroughly clean the eyelet boards.

Cleaning the boards is challenging, since there are a lot of passive components crowded together and it is hard to get to every square inch of the board. With persistence and the right tools, it is possible.

How to Clean the eyelet boards:

The amp should be partially dismantled to be cleaned. You want to remove the pots from the chassis mounts, but you don't have to disconnect or un-solder the leads. Un-solder the ground leads from the brass grounding plate and remove it for cleaning. Remove the eyelet board mounting screws, and lift the board up enough to get a little paintbrush under the board and between the backing board. Do the same for the bias board and the rectifier board, if there is one. Don't worry about the tube sockets, they can be cleaned in place.

The cleaning procedure was as follows:

1. Red Scotch-Bright pad to remove rust and corrosion from the chassis and the brass grounding plate, especially behind the grounding plate. Also the top edge of the chassis, so it will make good contact with the shield screen in the cabinet.

2. Vacuum up all the debris.

3. Liberal application of Krud Kutter to boards and etc.

4. Scrub with toothbrush and little paintbrush. Not only the surface of the board but also the individual components on the board, and the wiring. Do a small section at a time, and don't let the Krud Kutter dry. This takes a while...

5. Corroded solder joints attacked with brass brush.

6. Repeat steps 3-5 several times, until the board and components look like new.

7. Rinse and brush with denatured alcohol a couple of times. let dry between applications.

8. Apply De-Oxit to boards, pots, and switches. Spray directly on the boards and components. Get into hard to reach areas by using a little paintbrush. De-Oxit the pots in the usual way. Use original De-Oxit, not Gold.

9. Re-assemble. re-solder all grounds. Touch up any suspicious looking solder joints.

10. Let dry for a day or so. Then bring up slowly on a Variac while checking for any bad behavior.

This worked quite well on the worst contamination I have ever seen on a 1972 Super Six Reverb chassis which had been left out in a garage for 35 years. You can see more of this restoration here:
http://hardway.quantum-foam.com/fender-super-six-reverb-restoration.html


Here are Before / After photos:
B4.png


AFTER.jpg


Best Regards,

Don
 

pdf64

Member
Messages
9,187
Good work, well done:aok
Are you sure all those white plastic ecaps used for cathode bypass etc are good?
I'd be surprised if some haven't developed high ESR.
What have you done about the ecaps in the power supplies?
 

MKB

Silver Supporting Member
Messages
9,469
I once had a Marshall 1959 head from the 70s that always sounded a bit off, just weak and uninteresting. After a few years I had the PCB out, and noticed about 1/32" of crud on the trace side of the PCB. I cleaned all of that gunk off, and it radically improved the tone. So more amps can benefit from a good PCB cleaning.
 

eolon

Gold Supporting Member
Messages
509
Good work, well done:aok
Are you sure all those white plastic ecaps used for cathode bypass etc are good?
I'd be surprised if some haven't developed high ESR.
What have you done about the ecaps in the power supplies?

I checked all the caps with an in-circuit ESR tester, and they were all fine. I tested the electrolytic capacitors and they were also good.
This amp hadn't been turned on in maybe 35 years, so I brought it up in stages on a Variac to form the filter caps. The amp sounds great and performs really well.
I think sometimes people change filter caps when they really don't need to. Just because an electrolytic cap is 40 years old doesn't mean it is bad.

Best Regards,

Don
 

TimmyP

Member
Messages
2,488
You do not want DeOxit residue on anything that gets hot. It turns into a goo that is then harder to remove than whatever it was that you cleaned off before putting the DeOxit on there.
 

neteraser

Member
Messages
1,993
Definitely a nice idea, but I'd think dry methods of cleaning the board and CC resistors should be better..
 

Shiny_Beast

Gold Supporting Member
Messages
11,630
I had a turret board get so crusted in solder dust from modding that it started created problems.
 

eolon

Gold Supporting Member
Messages
509
You do not want DeOxit residue on anything that gets hot. It turns into a goo that is then harder to remove than whatever it was that you cleaned off before putting the DeOxit on there.

That has not been my experience. I use D5 on everything, it is rated up to 200 degrees C. (392 F.). I certainly don't see or feel any residue on the boards - D5 has a "protectant" but I don't know what it is. The main reason for using DeOxit is because it removes contaminants that have bonded to the solder joints and the eyelet boards. Regular solvents, like alcohol, do not do that. Denatured alcohol and of course Krud Kutter contain water. Alcohol absorbs water readily, which is why I flush the boards with it after using KK; when the alcohol evaporates, it takes much of the water with it. Alcohol also dissolves wax and oil, which is present on the vintage eyelet boards. The wax traps dust and other contaminants which is why board can become conductive as they get dirty . DeOxit displaces remaining water, so it is a good final step after cleaning with KK and alcohol. I don't like DeOxit Gold because it leaves a gooey residue.

Best Regards,

Don
 
Last edited:

tele_player

Member
Messages
733
I'm pretty sure the wax coating only started appearing on boards a few years into the silver face era, added by CBS as an attempt to cure the earlier boards tendency to absorb moisture, becoming conductive.

Your cleaned up amp certainly looks better. My inclination, if I had an amp like that, would be a complete rebuild. Kudos to you for bringing it back to life.

I'm amazed, but many modern builders still use the old style boards. Even my '99 Allen Accomplice, where the board is already warped like an old Fender. Allen doesn't use paper boards anymore. I'll probably rebuild it one of these days, though it's not having any problems.
 

67super

Member
Messages
1,504
I checked all the caps with an in-circuit ESR tester, and they were all fine. I tested the electrolytic capacitors and they were also good.
This amp hadn't been turned on in maybe 35 years, so I brought it up in stages on a Variac to form the filter caps. The amp sounds great and performs really well.
I think sometimes people change filter caps when they really don't need to. Just because an electrolytic cap is 40 years old doesn't mean it is bad.

Best Regards,

Don
I'm curious, did you check the white caps values in circuit or disconnected ? My experience is they almost always have drifted up in value even if esr is ok.
 

eolon

Gold Supporting Member
Messages
509
I'm curious, did you check the white caps values in circuit or disconnected ? My experience is they almost always have drifted up in value even if esr is ok.

I disconnected them to check capacitance values. They were all within 15% of their specification. As you may know, you kinda have to disconnect capacitors from a circuit to measure them because in-circuit you can get false readings from parallel capacitance nearby. The resistors were all checked as well, and were within about 15% of the spec. Remember from the factory the passive components were only spec 20%, so this isn't bad. I think although the amp was dirty, it wasn't played very much at all, and just sat for 35 years, so maybe that has something to do with it. Only found one bad blue gumball Paktron, which I replaced with an identical (good) Paktron I had lying around. The amp has no problems, no funny noises, it's nice.

By the way, I got an inexpensive ESR / DSR in-circuit tester on ebay a long time ago; it works fine - it just tells you "OK, BORDERLINE, and BAD" but it's good enough for rock and roll.

Best Regards,

Don
 

67super

Member
Messages
1,504
I disconnected them to check capacitance values. They were all within 15% of their specification. As you may know, you kinda have to disconnect capacitors from a circuit to measure them because in-circuit you can get false readings from parallel capacitance nearby. The resistors were all checked as well, and were within about 15% of the spec. Remember from the factory the passive components were only spec 20%, so this isn't bad. I think although the amp was dirty, it wasn't played very much at all, and just sat for 35 years, so maybe that has something to do with it. Only found one bad blue gumball Paktron, which I replaced with an identical (good) Paktron I had lying around. The amp has no problems, no funny noises, it's nice.

By the way, I got an inexpensive ESR / DSR in-circuit tester on ebay a long time ago; it works fine - it just tells you "OK, BORDERLINE, and BAD" but it's good enough for rock and roll.

Best Regards,

Don
I appreciate your post, it's very interesting. Yeah, I do know you have to take caps out of the circuit to measure. I've had to tell a lot of people that over the years, when it's in the circuit your measuring the circuit, not the cap.

Kind of related to your original topic, one of my main gigging amps is a 68 DR. When I bought it, it had been in a damp basement. I cleaned it up and got it working well but the volume would never completely go to zero. You could always hear some signal. Basically the eyelet board was so damp it would conduct signal through the board. I placed the amp in a dry, climate controlled area and over time it completely dried out and the issue went away. It's been one of my favorite amps for years.

I also bought a cheap ESR and dedicated cap meter on Ebay and they seem to work OK.
 

eolon

Gold Supporting Member
Messages
509
I appreciate your post, it's very interesting. Yeah, I do know you have to take caps out of the circuit to measure. I've had to tell a lot of people that over the years, when it's in the circuit your measuring the circuit, not the cap.

Kind of related to your original topic, one of my main gigging amps is a 68 DR. When I bought it, it had been in a damp basement. I cleaned it up and got it working well but the volume would never completely go to zero. You could always hear some signal. Basically the eyelet board was so damp it would conduct signal through the board. I placed the amp in a dry, climate controlled area and over time it completely dried out and the issue went away. It's been one of my favorite amps for years.

I also bought a cheap ESR and dedicated cap meter on Ebay and they seem to work OK.

I love my 66 Deluxe Reverb; it's one of my top three amps of all time. The eyelet boards on these amps almost always end of warping from weather and humidity and heat - some quite spectacularly.
The warping can lead to solder cracking and funny noises. An old trick I have used is to back out the three (or two) mounting screws to relieve the stress on the board. It's a cheap fix and it often works to get the amp working properly again in a hurry. My son would call it a "hobo" fix, but what the heck.

Best Regards,

Don
 




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