Fender Ultimate Chorus - bad hum

[drp555]

I have a Fender Ultimate Chorus, its about 9 - 10 years old, not the DSP. It now has a horrible hum when turned on. Even with no guitar plugged into the amp. If I turn the chorus on, the hum gets even louder and bassier. Sound still comes out if I plug a guitar in and play, but there's crackle and fizz with all the notes.

Any help or thoughts would be appreciated.

[cbarrow7625]

Two things come to mind immediately:

1.) Cracked ground trace (input jack maybe?) that is disrupting the ground continuity in the circuit.

2.) Filter caps. Have you checked them? Do you have the proper DC running through the amp? How much ripple do you meause on the DC rails?

Filter caps would be a 120Hz hum. Ground trace would be 60 Hz. Can you tell which it is? I don't know what piano notes those two frequencies are off the top of my head but I'm sure someone else here can tell you. If you can figure out the tone, you will be that much closer to solving your problem.

[Enzo]

FLip the main board over and check the solder to the main filter caps. I bet it is cracked - resolder them.

[drp555]

Thanks guys. I got a chance to check out the board today. Turns out one of the filter caps did have a cracked solder joint. I fixed that up and now everything is good.

[grcarson]

had the same problem. Thanks for the fix.

[Showey]

Ultimate Chorus issues.

Had the same issue here. Fixed that but the reverb doesnt seem to work although when I tap on the reverb unit I can hear the effect thru the speakers. Any ideas?

[Gtr_tech]

Had the same issue here. Fixed that but the reverb doesnt seem to work although when I tap on the reverb unit I can hear the effect thru the speakers. Any ideas?

Lunched rev drive IC is likely. Or a bad coil/connection to the coil on the drive side.

[Showey]

I found it. bad coil on the INPUT side of the reverb tank.
New reverb can installed 20.00 from ebay and all is well!
Thanks!

[Showey]

Today I swapped it for a Peavey Delta Blues 115 Tube Combo Amp.
I think its a good thing?

[ButchHutch]

main filter caps

Hi all,
I just found this Post, looking for a fix on my Amp (Fender Ultimate Chorus PR204 ) It seems I have the same problem can someone post a pic of what the the main filter caps look Like I would like to try and fix This myself / plus I can't find anyone in this town to work on a SS amp .... I love this amp and realy want it back in good working order..

Thanks in advance for any advice and help

Butch

[ButchHutch]

schematic part

or a part (Number/Letter) on the schematic.... I have the schematic for this amp (Fender Ultimate Chorus) and 1 for the (Fender Ultra Chorus PR204) I think there the same

PS: my amp is the Fender Ultra Chorus PR204


Thanks, Butch

[Jazz P Bass]

If you cannot identify the power capacitors, how can you feel confident that you can repair the amplifier.
You can get hurt real quick "messing" with the power supply.
I do not have a schematic.
If you have one, post it.

[ButchHutch]

all I can do is see what info I can get to try at this Point
If some can point out where it's at on the Board, then I can look on it for a cracked solder joint ...

[Ronsonic]

Hi all,
I just found this Post, looking for a fix on my Amp (Fender Ultimate Chorus PR204 ) It seems I have the same problem can someone post a pic of what the the main filter caps look Like I would like to try and fix This myself / plus I can't find anyone in this town to work on a SS amp .... I love this amp and realy want it back in good working order..

Thanks in advance for any advice and help

Butch

The filters are pretty obvious. They are the tall cylindrical things standing above the circuit board with the cracked solder joints on the other side. Do not be bashful about resoldering anything that looks like it might want more metal on it. Be sure to have the outputs clamped down to the chassis on their heatsink before running the amp, even for a short test.

[Jazz P Bass]

Thanks for the scheme.
The filter caps in question are located at coordinates C-8 on the layout diagram. C-84 & C-85.
They will be over on the left side of the board.
Be real careful when you remove the board.
If any wires have to be removed when disassembling the amp, write down where they go.
The output transistors are mounted to a backplane.
The backplane itself can be removed as a unit. Leave the transistors attached.
After all that to get the board out, simply resolder the caps.
Unless you know what to look for, you will not see a bad solder joint.
(Then again it may be glaringly obvious)