peavey 400 problem

[Eddy lonergan]

I`ve got an old peavey 400,
and last year at an open air gig,he gave out.
it was 30 degrees on stage,and the only way to describe the problem is.
it`s making a zweep,zweep,zweep,zweep,sound when i add reverb,i can`t
trust the amp to play with an external reverb pedal,for two reasons.
it might pack up all together in the middle of a gig,song.
And i really do love this amp and don`t want to lose it through pushing the problem further.
Is there anybody out there who can or has had the same dilemma and solved the problem.
and would be willing to pass on the solution,so as i can tell the technical expert what is exactly wrong,without getting billed
for unnecessary work and time.
Eddy

[nashvillebill]

Peavey had several versions of a 400 amp, can you post a picture or two? Once we can figure out exactly what version it is, we will try to help.

How good are your electronic troubleshooting skills, and do you ahve any test equipment such as a digital multimeter (DMM)?

[Eddy lonergan]

Nasvillebill

EDIT: There was photo linked here, but it's gone dead.

Howdy doody Nasvillebill.
The link to the amp is a coincidental title.but appropriate.i tried to upload an image of mine,but this seemed to be the best short cut.
This old beast has been with me a long time,and i`m not yet ready to take old yeller into the backyard.
It`s the peavey 400 chorus,2 x scorpion speakers push and pull knops,the problem started last year.
i`m trying to think how to describe the problem, when i add reverb the volume decreases and it begins to make a
sweep sound,it`s stupid i know but if you say this word quickly it does sound like the problem at hand.
sweep,sweep,sweep,sweep.
this just takes over and there`s no joy at all,you asked if i had a dmm meter,i`m sure the local d.i.y. has one.
I have had it out the cabin and hoped to see a loose connection or some overheating but alas my hope for a simple solution
where deflated.
I know when to leave things well alone if i can`t see the problem,especially elec -tech and call in someone who does know his or her stuff.
I would like to think i could fix it myself with the likes of you guys on this forum,but it will have to be in baby steps.
now your thinking Nasvillebill,why the heck did i answer this guy?
Well see it as a double challenge,the problem with the amp is pretty easy for you i imagine,
The biggest mountain to climb is telling me how to fix it HAHAHAHA.
anyway if you decide to give up,not a problem i understand,
but i hope you can sleep at night knowing old yeller is going out into the backyard.
good luck and good health
Eddy Lonergan

[Jazz P Bass]

As much as I would like you to fix the amp. I don't see ity happening without proper test equipment & service tools.
I have attached the schematic.
The Reverb circuit consists of the reverb driver (IC16B), the reverb pan and the reverb return (IC18A).
It sounds like one of the ic's is oscillating.
That could be due to a bad ic or maybe a leaky capacitor in one of the circuits (drive or return)
An oscilloscope would help immensely, although you may be able to track down the problem with a DVM.

[Eddy lonergan]

As much as I would like you to fix the amp. I don't see ity happening without proper test equipment & service tools.
I have attached the schematic.
The Reverb circuit consists of the reverb driver (IC16B), the reverb pan and the reverb return (IC18A).
It sounds like one of the ic's is oscillating.
That could be due to a bad ic or maybe a leaky capacitor in one of the circuits (drive or return)
An oscilloscope would help immensely, although you may be able to track down the problem with a DVM.

Thanks Jazz P Bass.
when can you come over,this evening?
We live in Rolde,Netherlands,Europe.
would 8 oclock be alright,coffee will be perculating or a cold one in the fridge if you prefer.
so its a big job then?????????????
old yeller is looking older
Eddy lonergan

[nashvillebill]

Thanks for posting the schematic, Jazz P Bass.

Yep, unfortunately there's only a limited amount of assistance we can offer if someone doesn't have access to some test equipment. However, there are a couple of things to try first.

When you start to add reverb, hit the amp hard enough with your hand to make the reverb springs shake. Can you hear the noise from the springs despite the other noise?

The IC's are socket-mounted on this amp. Make sure IC number U18 is firmly seated (check the schematic Jazz posted, look at the layout and it shows which one it is).

Without test equipment, just about the only other thing that could be done would be to replace U18. It doesn't have to be a 4558, it could be replaced with a NE5532 (both the 4558 and NE5532 are common though and here in the States they are very cheap, less than a dollar). Note where the dot is on the old IC before you pull it, match the new IC dot to the same orientation (its shown on the layout too). Just make sure all the legs go into the socket correctly.

[Eddy lonergan]

Thanks you guys .
at least i can tell the tech,where to look for the problem.
we might be able to save the old dog after all.
Nashvillebill and Jazz P Bass also thanks for the sat nav attachment of the peavey,
I`ll print that off,for the unlucky fella who has to repair it,
with your suggestions.
take care and good luck and good health to you both.
Eddy Lonergan

[Enzo]

What Bill said. 400 is not a Peavey model, it is part of a model name.

Has this happened anywhere else than that outdoor gig? Were you on generator power or running on the mains? Does the problem ONLY affect the reverb, in other words if the reverb remains off, does the amp play well otherwise?

I appreciate the desire to save money, but if someone else had a similar problem, it may not be from the same cause. Sending a technician down a false path with a faulty clue will not save you money.

[Eddy lonergan]

Hello Enzo,
Its a peavey 400 chorus,push and pull knops,and yes it did happen at a gig,with generator power.
and i was thinking myself that it had got a surge,thats why i took it out of it`s cabin to see if there was any visible damage.
But like i said to Bill and jazz there was nothing at all to go on.and yes the amp is okay till you add a touch of reverb,then it starts this ,sweep,sweep,sweep,sweep sound and volume decreases
like a limiter has been turned full on.
Jazz attached the print diagrams,its not a question of saving money but saving unnecessary costs,their diagnosis seems a pretty logical one and i`m really thankful
and its only something i can point out to the tech guy when i take it to him,maybe it is something else,but this is more info than what i had.you guys live across that big pond
and peavey roams through the hills and valleys,here its another story,little village tech guy needs a sat nav,so any info is welcome.
I really do love this amp its been all over europe with me,and i would like to save it.i could get another but this old dog feels like an old pair of boots.
anyway thanks for the input and if you have any ideas their welcome.the more things the tech guy has to go on the better.
thanks
Eddy Lonergan

[Enzo]

I guess I still am not sure, does the amp do this wherever it is used, or did it ONLY happen at this one outdoor gig?

[Eddy lonergan]

peavey 400

hello Enzo,
It started at the open air gig,after that at the practice location,but not all the time.
then it was more frequent,and now constant with reverb added.
No reverb its okay,but i think once something is on its way out and not fixed,
something else will soon follow,like an old car.
thanks anyway
Eddy Lonergan