Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

On 7/16/2020 11:23 AM, wrote:
Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

Can you post a link to the schematic? This will help others help
you even if you can't read it yourself. The exact model number
and a photo will also be helpful.

None of the Princeton models that I found have the chips you describe. Can you post the exact model from the plate? The only Princeton Chorus model I found has DSP in the model name as well.

I have some hardcopy schematics around that I will check as well, but any additional info you can provide will help.

Dan

On 7/16/2020 5:35 PM, abrsvc wrote:
None of the Princeton models that I found have the chips you describe. Can you post the exact model from the plate? The only Princeton Chorus model I found has DSP in the model name as well.

Same here. That's why I asked the OP to provide more details. I
couldn't find any model using a BBD.

Without the schematic, based upon the symptoms described:

1) The "delay" portion is working as expected
2) The delayed signal amplitude is smaller than expected. This would suggest that there is likely an op-amp down stream that is not working correctly or at all. Look for a TC072 or perhaps a 4558 IC that is faulty post the MN chips.

Dan

On Thu, 16 Jul 2020 06:45:11 -0700, abrsvc wrote:

Without the schematic, based upon the symptoms described:

1) The "delay" portion is working as expected 2) The delayed signal
amplitude is smaller than expected. This would suggest that there is
likely an op-amp down stream that is not working correctly or at all.
Look for a TC072 or perhaps a 4558 IC that is faulty post the MN chips.

Dan

Or high ESR coupling cap?

abrsvc wrote:

=============

None of the Princeton models that I found have the chips you describe.


----------------------------

See:

http://www.kobra.hr/Schematics/Choru...o%20Chorus.jpg


The repair is a job for an experienced amp tech with the usual test gear on hand - scope, audio gen etc.



..... Phil

On Wednesday, July 15, 2020 at 10:53:29 PM UTC-7, wrote:
Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

On Wednesday, July 15, 2020 at 10:53:29 PM UTC-7, wrote:
Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

Thanks for your help everyone, however, the IC's MN 3101 and MN 3007 are stock parts that came out of my completely stock virgin 1988 Solid State Fender Princeton Chorus amp. Not sure why you're not seeing them ?

On Wednesday, July 15, 2020 at 10:53:29 PM UTC-7, wrote:
Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

On Thursday, July 16, 2020 at 5:05:30 AM UTC-7, abrsvc wrote:
None of the Princeton models that I found have the chips you describe. Can you post the exact model from the plate? The only Princeton Chorus model I found has DSP in the model name as well.

I have some hardcopy schematics around that I will check as well, but any additional info you can provide will help.

Dan

Thanks Dan,

My 1988 Fender Princeton Chorus Model PR82 Made In USA is completely stock, a totally virgin amp. The IC's MN 3101 and MN 3007 are stock parts that came out of this amp. I replaced them with new ones yesterday, but no change, the Chorus is still having problems. The pilot light comes on, and both the Rate & Depth controls seem to be working, but the FX is very very weak.

BTW...this is not a Princeton that uses DSP...the amps that featured DSp effects came after the PR82 models and don't sound near as good.

Stay Safe, Charles

On Thursday, July 16, 2020 at 2:52:19 PM UTC-7, Phil Allison wrote:
abrsvc wrote:

=============

None of the Princeton models that I found have the chips you describe.


----------------------------

See:

http://www.kobra.hr/Schematics/Choru...o%20Chorus.jpg


The repair is a job for an experienced amp tech with the usual test gear on hand - scope, audio gen etc.



.... Phil

On Wednesday, July 15, 2020 at 10:53:29 PM UTC-7, wrote:
Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

On Wednesday, July 15, 2020 at 10:53:29 PM UTC-7, wrote:
Hello, I have a 1988 Fender Princeton Chorus amp, I believe this was the first year model.

I have a faint chorus sound/FX in both the rate & the depth controls.

I replaced the MN 3007 & MN 3001 chips today, but still no real change. The chorus FX is there, but really faint.

Both speakers are working, both sides of the amp seem to be working and the amp is totally stock. Nobody
has changed anything except for what I did today.

Can you help me ? Maybe tell me what else to change ?

I cant read a schematic at all, so please if you could be so kind, please explain where to find the parts that
you might suggest that I try changing.

Stay safe, Charles

NOTE: I live at least 200 miles from the nearest repair station so I'd really like to fix this problem myself with your help of course

My 1988 Fender Princeton Chorus Model PR82 Made In USA is completely stock, a totally virgin amp. The IC's MN 3101 and MN 3007 are stock parts that came out of this amp. I replaced them with new ones yesterday, but no change, the Chorus is still having problems. The pilot light comes on, and both the Rate & Depth controls seem to be working, but the FX is very very weak.

BTW...this is not a Princeton that uses DSP...the amps that featured DSp effects came after the PR82 models and don't sound near as good.

Stay Safe, Charles

First of all Phil is probably right. But then if you want to try things on your own...

The chips you mentioned are probably the clock and BBD. They really should not affect the level of sound.

Turn the chorus off and see if you are getting the same volume out of each speaker.

If the sound is equal then you need to go right after the BBD circuit. If not it could be in the amp on that side anywhere.

There is an OP AMP right after the BBD, it is set to unity gain. If you have a scope, it should be putting out the same amplitude as what is going in.

It is nice to have a generator working in those things but you have to usually resistor the output way down. Where I worked I had a guitar next to me, plugged it in and had to strum it periodically. My stuff stays home now.

That print says for a power/gain test go in the return loop jack and you should have equal signal on both sides. You can plug a friggin cassette deck into it really. (one channel) All you have to do is get or make the proper adapter.

Jeff Urban wrote:

============================

First of all Phil is probably right.

** You bet he is...

But then if you want to try things on your own...


** He might start with the Chorus/ straight switching system. In Chorus mode, one channel handles straight signal while the other the delayed/swept version.

Mixing of the two to give the effect occurs in the air beyond the speakers.
If the either channel's level is low, he may still think both speakers are workings when one is not.

I use a scope to tell, the delayed signal sounds almost normal until the straight one is added.


...... Phil

Well like you said but in different words, this takes a tech. One speaker could be half blown. And in a guitar amp post people would not notice much if the amp is only pushing one direction.

I say let the guy do it. I think he owns it. If it goes poof then it does.

Maybe the guy will buy a scope. I think novices should always start with a CRO, not a raster based one. No digital no nothing.

That would ell of the speakers. They both had the same power but one (the right one I think right ?) is half ****ed up because maybe something got spilled in it. **** happens.

Well if out OPer here is reading he is probably learning. One of the simplest tests would be to switch the speakers. However we know that is not always feasible. You got two viable choices, mount them reverse. Or just hook it to external speakers. We all have a pair of speakers around.

So without a scope he is not even to that point yet, needs a pair.