Looking To Repair an old Fender M-80 - help/advice?

[joel_ostrom]

I bought an old fender M-80 solid state amp from a friend at college, great sounding amp but in need of some tune ups. The pots are very crackly (all of them), so i'm thinking i'd like to replace them all. I'm trying to locate a good online dealer for some parts of good quality.

The pots that are in this one are PC bracket mounted pots of varying values. Would it be difficult to simply buy some plain non-PC mount pots and jumper them to the board? i'm having trouble finding a supplier of the bracket/snapin type of pots.

Also, i'm wanting to replace the input jacks. They're also PC mounted components, but they're the Fender 9-pin type. Is it possible to install a standard switchcraft metal input jack and (again) jumper the terminals to the board? It seems reasonable, considering that the only thing being plugged into the jack is a mono phone plug with 1 signal and 1 ground terminal.

Lastly, i'm a bit of a newbie at component values and such, could anybody help me out with the meanings of these types of values? (these are the pot values for the ones i'm hoping to replace):

15A50K
15A2K
B50K
30C100K
30C50K

i've seen lots of pots with values like 50K and 100K and such, but i'm confused about what the values "30C" and "B" mean.

Any help is greatly appreciated,
Cheers!
Joel

[soundguruman]

I bought an old fender M-80 solid state amp from a friend at college, great sounding amp but in need of some tune ups. The pots are very crackly (all of them), so i'm thinking i'd like to replace them all. I'm trying to locate a good online dealer for some parts of good quality.

The pots that are in this one are PC bracket mounted pots of varying values. Would it be difficult to simply buy some plain non-PC mount pots and jumper them to the board? i'm having trouble finding a supplier of the bracket/snapin type of pots.

Also, i'm wanting to replace the input jacks. They're also PC mounted components, but they're the Fender 9-pin type. Is it possible to install a standard switchcraft metal input jack and (again) jumper the terminals to the board? It seems reasonable, considering that the only thing being plugged into the jack is a mono phone plug with 1 signal and 1 ground terminal.

Lastly, i'm a bit of a newbie at component values and such, could anybody help me out with the meanings of these types of values? (these are the pot values for the ones i'm hoping to replace):

15A50K
15A2K
B50K
30C100K
30C50K

i've seen lots of pots with values like 50K and 100K and such, but i'm confused about what the values "30C" and "B" mean.

Any help is greatly appreciated,
Cheers!
Joel

First, you usually don't need to replace them, just use high quality cleaner, deoxit D100, followed by deoxit fader lube.
On this amp, take the controls off the board and clean them, then put the controls back in, because of the shape and size, it is difficult to spray into the control without removing it first. You could, clean them without removing them, but it's almost easier to remove them first.
Using cheap cleaner is a big mistake.
Second, fender will supply the exact parts, and you can order them from a dealer. I pay less than $2 each for the original replacements. You may not be that fortunate.
30C, B, etc...is the taper of the control. The response curve VS. position of the setting, like audio taper, linear taper, etc...
Third, replace ALL the jacks. On this amp, the jacks oxidize and the amp will fail because of that. Cleaning may not really produce the ideal result.
There are some generic replacements that cost about $2, and these usually work just fine. You can order them (original or generic) from antique radio supply in Arizona. The original jacks cost a lot more, and are barely better than the generic ones.
Since the Japan earthquake, I have seen factory amps with the generic jacks installed instead of the original type, right from the factory. Probably a shortage of the originals.
All these plastic type jacks break easily, in normal use. Won't matter if they are Fender or generic, they both break easily.
No, it is not practical to use substitutes, like switch craft, you need the ones that are made to fit the board. It will save a lot of time. There are all kinds of switch contacts inside the jack. The contacts must be functional, or the amp won't work correctly.
Fourth, It is a very challenging and time consuming job, that requires a temperature controlled soldering station, and lots of skill.
If you are not an expert, you could easily damage the circuit board. And I have seen amateurs try to do this, and they destroyed the thing, I mean a real bloody mess....
It will take an experienced person hours to do the entire job correctly. And that's a person who knows how, and has the correct tools.
In other words, this is NOT the amp to "learn how" on. Then again, it's still easier to work on than a Mesa Boogie. So I would say, difficulty: "medium."
If you are thinking about this, and don't have substantial experience, I do not recommend you attempt it. It's a harder amp to work on than many other common amps.

[joel_ostrom]

First, you usually don't need to replace them, just use high quality cleaner, deoxit D100, followed by deoxit fader lube.
On this amp, take the controls off the board and clean them, then put the controls back in, because of the shape and size, it is difficult to spray into the control without removing it first. You could, clean them without removing them, but it's almost easier to remove them first.
Using cheap cleaner is a big mistake.
Second, fender will supply the exact parts, and you can order them from a dealer. I pay less than $2 each for the original replacements. You may not be that fortunate.
30C, B, etc...is the taper of the control. The response curve VS. position of the setting, like audio taper, linear taper, etc...
Third, replace ALL the jacks. On this amp, the jacks oxidize and the amp will fail because of that. Cleaning may not really produce the ideal result.
There are some generic replacements that cost about $2, and these usually work just fine. You can order them (original or generic) from antique radio supply in Arizona. The original jacks cost a lot more, and are barely better than the generic ones.
Since the Japan earthquake, I have seen factory amps with the generic jacks installed instead of the original type, right from the factory. Probably a shortage of the originals.
All these plastic type jacks break easily, in normal use. Won't matter if they are Fender or generic, they both break easily.
No, it is not practical to use substitutes, like switch craft, you need the ones that are made to fit the board. It will save a lot of time. There are all kinds of switch contacts inside the jack. The contacts must be functional, or the amp won't work correctly.
Fourth, It is a very challenging and time consuming job, that requires a temperature controlled soldering station, and lots of skill.
If you are not an expert, you could easily damage the circuit board. And I have seen amateurs try to do this, and they destroyed the thing, I mean a real bloody mess....
It will take an experienced person hours to do the entire job correctly. And that's a person who knows how, and has the correct tools.
In other words, this is NOT the amp to "learn how" on. Then again, it's still easier to work on than a Mesa Boogie. So I would say, difficulty: "medium."
If you are thinking about this, and don't have substantial experience, I do not recommend you attempt it. It's a harder amp to work on than many other common amps.

Wow, thanks for the info.

If i can help it i'd really almost prefer to just replace the pots completely. The trouble i'm having is just finding a good enough dealer with the right supplies. Its been hard to find one that carries the exact kind of brackmount/snapin pots with the correct values. I have found exact fender replacement parts but they were at least $9 a piece. I'm not willing to spend that much to replace all the pots.

I will however definitely replace the jacks. I've found the generic replacement 9 pin jacks on mojotone.com - i'm just disappointed that i have to resort to using the plastic kind again. I don't like plastic components for the sheer fact that they're so fragile and will break easily. but w/e i guess...

i understand the importance of matching the values of the pots with what's already in the amp, but could i get away with getting pots of a different type? (i.e. not pcb mounted pots, or the "snapin" type). couldn't i simply jumper the terminals to the correct traces on the board?

I know you said its a bad idea for the input jacks because of all the important contacts that have to be made, but as for my level of expertise i'm not exactly a newb with a soldering iron and on PCB work. I have done it before with no problems. And i have a good solder iron with temperature control.

do you have any good sites that i might try checking out as a parts source? (important, they must ship to canada)

here's a few that i've tried with no luck: Small Bear Electronics, Watts Tube Audio (turretboards.com), Amp Repair Parts.com, Mouser.com,

if you have any other sources that you think might be good please let me know

thanks again for the tips!

[Enzo]

I see no reason to take the controls off the board. There is an opening in each control where the legs come out - you spray cleaner into that hole. If you look down into the chassis, the hole facecs downward and would be difficult to sprat up into. SO hold the chassis up and look up at it from underneath. Now the opening is on top of the control. It is still not imediately accessible, but if you hold the end of the spray tube right against the control wafer and spray, the fluid will then run down into the opening and clean the control. Takes only a couple minutes and no solder required.


I would agree that most times the controls will clean up just fine.


I highly recommend replacing any bad jacks with the real Fender part. You may be shoving just a mono plug into the jack, but the extra pins handle switching chores. One set of pins is involved in muting the amp when the jack is empty. Other contacts ground the tip when teh jack is empty, and we also have the hi/lo resistors to switch. It really isn't worth the effort to cobble something else in there.

ANy Fender dealer can order parts for you. There are various suppliers, Antique Electronic Supply is one, or google "fender parts" and there will be several suppliers listed.


You COULD find pots to fit the holes and run wires to the circuit board, but real parts make a lot more sense, they fit the board, they fit the holes, they fit the knobs, and they fit the application.

From the schematic, your part numbers are:

027937 2K (A15) R31 mids
027940 50k (A15) R29,R30 treble, bass
027941 50k (lin) R23,R45 contour, reverb
027943 50k (A30) R24,R37 ODvolume, clean
027947 100k (30) R16,R25 gain, presence.

COnsidering that the amp is 20-25 years old, it is highly likely Fender no longer has those, so you may need to hunt for them.


All the more reason to clean the old ones.

[soundguruman]

Call Fender customer service and get all your part numbers, for all the parts. Use the factory part numbers, make a list.
Once you have the part numbers, and you're not trying to order by description, you can try to ask Joe to order them for you.
It's just one source that I use...E mail him, include all the Fender numbers, and ask him to have Fender Drop Ship directly to you.
Just a guess, and I don't know if he will do it, but try the E mail. Other than that, the generic jacks can be ordered from tubesandmore.com
Lightning Joe's Guitar Heaven
100 East Branch Street
Arroyo Grande, CA 93420-2702
(805) 481-2226 phone
(805) 481-3689 fax
LIGHTNING JOE'S GUITAR HEAVEN
joseph@lightningjoes.com

[Enzo]

One thing you should know about pots used in amps. Or in most any commercial product. They are custom made for the applications. Fender or whoever does not go to Alps or someone and find th pots on the shelf. They select from charts of features:
Size of pot - 16mm, 24mm whatever
type of shaft - solid, D, split, knurl, smooth, etc
length of shaft
Bushing or no?
Threaded bushing?
detents?
support bracket or no?
pc terminals or solder lugs?
resistance
taper
And so on.

From those things, Fender will select what it wants, and the pot maker makes them.

SO you won;t find Fender pots at Mouser, you will find them at suppliers who get parts from Fender.

Now 100k or 50k are common values, so you may find the same pot in this Fender and also in some other brand amp, but that other brand may have a split shaft instead of the D shaft you have.

[soundguruman]

Well, I have had pretty good support from fender even on these older amps, worth a try.
Be sure to get the updated part numbers from fender customer service, the numbers have changed.
It's pretty staggering when you look at the list price, that's for sure.
I hate to mention it, but the parts that you are paying $9 for, I am getting for 89 cents. Yaaaaaaa!

[joel_ostrom]

Well, I have had pretty good support from fender even on these older amps, worth a try.
Be sure to get the updated part numbers from fender customer service, the numbers have changed.
It's pretty staggering when you look at the list price, that's for sure.
I hate to mention it, but the parts that you are paying $9 for, I am getting for 89 cents. Yaaaaaaa!

wow, could you tell me where i could also acquire such parts for $0.89 as well, haha

i located a dealer on eBay that has all the components i'm looking for, but the pots are $5.99 each. to replace 9 pots is getting a little pricey. I just want to make sure i've shopped around as best i could before i make a purchase.

[Enzo]

Welcome to the forum, by the way, Joel.


SO spray some darn cleaner into them, and see if this whole replacement deal is not necessary. Do you buy new reading glasses if the old ones get a smudge on the lens? Dirt is not a death sentence for a control. Dirty pots happen every day, and the chemicals designed for exactly that purpose work really well.

The worst that can happen is that you still need new controls. The best that happens is you do not, plus you have a can of cleaner for use on all the rest of the controls you will encounter in your life.


Parts-is-Parts lists all of them, at $5 each, can't tell you if they are currently in stock or not:
Fender Potentiometers | Guitar, Amplifier, and Korg Keyboard Parts | NATIONAL PARTS DISTRIBUTOR FOR KORG, VOX, BLACKSTAR. PARTS FOR FENDER, GIBSON, GRETSCH, HOFNER, SWR, GUILD, AND MUCH MORE

AES looks to have a couple of them for $2.75.

[DrGonz78]

Yeah pots last for a long time and can usually be cleaned to make almost new again. I recently cleaned pots on a late 70's Yamaha G100 and they work like a charm now. Also, those damn fender pots are way too expensive to replace more than one at a time to make it economical. Well, for us out here that don't have the .89 cent pricing.

I had this marshall 15 watt amp recently where I did not want to take off the pots to clean them and instead used rubber tubing. Go to Home Depot and find .75inch tubing... or I think that is what I got. Take the tubing (about 2-3 inches) and cut it nice and flat on the end you will push over the shaft of the pot. You simply put the tube snug onto shaft and just a nice spray into the tube. This does not always work that well but it is good on some pots, makes it a heck of lot easier. I tend to take the pots off to clean them since the lubricant in the cleaner gets on the PCB boards. However, sometimes you will find that you just spray into the pot without removing them, but to me I always make a lil mess.

There was a Princeton that I had to order the exact Fender pot and yeah Parts is Parts is a good source, but you pay in the shipping. It was like $9 total. I had a Fender FM212r that I ordered 3 alpha pots and bent off the side brackets to the original pots. I then connected a wire on the new pot to ground it to the two side pieces and soldered it into place. So it looked really stupid but it saved me $27 and it works just the same.

[soundguruman]

I think you are wasting your money on the pots. Take them out and clean them

[J M Fahey]

soundguruman wrote:
...........
I hate to mention it, but the parts that you are paying $9 for, I am getting for 89 cents. Yaaaaaaa!

soundguruman wrote:
...........
I think you are wasting your money on the pots. Take them out and clean them.
You wanna pay 89 cents for $10 pots, get in bed with a fender dealer hahaha.

So, you *are* getting in bed with a Fender dealer !!!!
Wow, thatīs frank and open on your part.
Didn't want to know that much, Michael Friedlander.
Are you *sure* you want to post that here?

[soundguruman]

I wonder pretty often why the markup is so high.

[Gtr_tech]

Keep in mind that Fender likes to use the support bracket on the back of the pots as a "wire" for gnd connections. You remove that bracket, you need to bridge the traces that went to it to keep the gnd connections.

[oc disorder]

I agree with the above ..a good clean with some decent Caig deoxit should fix it although the price of deoxit in Aust is approx $40 AU with freight so it may be cheaper to buy the replacements.
I would use originals to preserve the board integrity.
The possibility of problems down the track (no pun intended) due to stressed connections etc would be too high for me.

It's essential to make sure the cleaner gets right into the pot .. to make sure hold the board upside down and spray into the opening where the lugs/terminals leave the case and solder to the board.

On another note I recall an old Tripod page by Nat Cade that had some fender "briefings" ??? ummm service notes that now only exist on the wayback machine.

Tech Notes Part II - Fender

In particular this one

" June, 1993

M-80, M-80 Chorus Bias Modification
A resistor change is required in the power amp section to reduce the DC Bias current through the output transistors. The change will minimize the possibility of overheating.

M-80 :
Remove R74 & R76 (1K, 1/4W), and replace them with 2.2K, 1/4W carbon film resistors.

M-80 Chorus :
Remove R127, R129, R154, R156 (1K, 2W), and replace them with 2.2K, 2W carbon film, or metal film resistors.

M-80 Bass Power Supply Modofications
A resistor change is required in the power supply section to reduce the amount of current through the 16 volt zener diodes CR49 & CR50. This will minimixe the possibilty of the zeners overheating.
Remove R144 & R145 (270 ohm, 7W), and replace them with 390 ohm, 7W wire wound resistors. Make sure to glue the resistors to the p.c. board using an RTV silicone compound. "

As this is dated 1993 your model may have already had the alterations.

Anyway thats my help/advice

Good Luck !!!