Fender Deluxe Reverb Re-Issue (Standby making electrical discharge sound)

[Ryteone]

I want to thank Loosechange he has been helping solve the problems I've run into in this simple cap change.  Now I'm stuck on this last one.  When you put the amp on standby it makes a fading electrical discharge sound (fading like when you play a note and put an amp on standby).  I'm also finding some DC on the Normal and Vib Volume pots when your rotate them quickly back and forth you hear a some static.  The rest of the amp is very quiet and stable.  I had some problem with the treble pot on the vib channel giving me some oscillation when turned up past 6 or 7 with the volume up past 5 (check all my connections and repair of the circuit board pads that lifted and removed the bright cap C10 and it seemed to clear it up).

I've attached a PDF with the schematic with blue dots for the caps I pulled and checked for DC leakage (per instructions I read on he form here, by lifting the negative side and checking each).  The green color dots are for the items I had changed per customers request with a Fromel kit he ordered.  (Yes I contacted Fromel and John said he hadn't heard of this before).  I also pulled each of those the same as the blue dots to check for leakage in the new caps.  So I figured I would go back to where I seem to get the best answers on the web (well amp and some other off base answers).

I didn't notice last night when I put a lower value cap in the bright cap C10 position (after having it removed) the discharge sound when put on standby was louder.

Any one every have a problem with standby sounds?  If so where did you find the problems.

Had almost talked the customer into letting me build a point to point replacement board from off here but didn't like the cost (would of been about the same labor I've got in testing this now, but limited to what I gave him as a price to change out those parts, not one to dick around people with faults that are most likely my creation, mark it up to learning fees on my part)

Thanks Scott...

[Ryteone]

I should also note I ran through the Fender test points and they all seemed with in range.  Just not sure how or where to start checking for other idea's.  Tried using my scope to run the path to watch the sine wave to see if I could see anything out of normal.  Nothing till I put it on stand by or turn the volume pots quickly (a bit of fine static along the sinewave).

[phsyconoodler]

What caps did you change with this fancy kit? Did you change any signal caps and are you positive you have a good ground for your new filter caps?

[Ryteone]

Changed out all 4 of the filter cap, all the caps in the tone stack (was supposed to more match the sound of the real 65 Deluxe).  All the cathode Bypass caps, two coupling caps and a few resistors (four for the tone stack, one for the feedback circuit).

[Fresh_Start]

Scratchy volume pots often means they have DC voltage on them when they shouldn't.  You replaced a crap load of caps (to use a technical terms) in that amp.

Check for DC voltage on pin 7 of both V1b and V2b.  If there's DC voltage on the preamp tube grid, you have to figure out which one of the preceding caps is leaking.  Did you use a heat sink every time when you re-soldered those new caps in?  I know I toasted a coupling cap in a new build after I thought I was really good at soldering and before I went back to using heat sinks as insurance.  Same symptom BTW.

This may be weird, but put the negative lead of your voltage meter on the safety ground bolt for the power cord and then measure for DC voltage where each Volume pot is supposed to be grounded.  My thinking is that it's odd that BOTH volume pots are scratchy...

Don't know if that will help,

Chip

[phsyconoodler]

Did you change the treble cap to a silver mica? If so,that is likely where the problem is.Leaky silver mica caps can ruin your whole day.

[LooseChange]

+1
I thought this issue was solved.

[Ryteone]

Almost just the DC static and the electrical discharge sound when placed on standby.  Noticed when I had the meter hooked up to the negative side of the volume pot or anywhere along the negative/ground plan of the circuit board it would kill the static sound on the volume pots.  The same thing happened when I was taking a reading on connectors from the cap can CP18 and choke connector SP1.  I tried cleaning the ribbon connectors & the crimp connectors (like the CP connectors), I also tightened up the crimp connectors to make a tighter connection.

I rebuilt the filter caps under the can just to rule out anything there.  I started to think maybe having a grounding issue with it cleaning up the static when I placed the meter to read for DC voltage between the ground plane on the board the pots are mounted too and the chassis grounding point.  But that didn't clean up the electrical discharge sound when placed on stand by.

Then I started to think about the choke or rectifier if they could cause some of the problems I'm having.

Scott.

[Fresh_Start]

So if you clip a simple jumper between the ground point of a Volume pot and a bolt on the chassis, the static goes away?  Or is it if you clip a jumper between the Volume pot ground point and something else in the circuit?

Did you read any DC voltage on grids of V1b and/or V2b?

Forgive me, but it doesn't seem like you have eliminated the most obvious possible culprits - either a leaky coupling cap in the tone stack or a weak ground connection between the PCB and the chassis.  Note - I'm assuming the board is grounded to the chassis somewhere.  If that connection uses a "crimp connector", cut it out and solder the darned thing before you start re-building more of this amp.

Here are a couple of references that may help:

http://www.el34world.com/charts/fenderservice6.htm

http://www.geofex.com/ampdbug/ampdebug.htm

Respectfully,

Chip

[Ryteone]

Sorry I got sent out of town to work, just got back in town.  I gave him his amp to use while I was gone.

There wasn't any DC voltage on the grids of V1b or V2b.  I tried using a jumper but it didn't work the same as when I use the DMM to read the DC voltage.  I'm guessing the meter is filtering it some how.  Yeah normally these are not too hard to sort out, just go back over my joints and make sure they are good, check components (yes seen new ones that are bad).  I always try to search on hear before I ever ask questions, figure someone has ran into the same problem as I have in the past.  But this one has had me running in circles.  The static on the pot isn't that bad till you turn the volume pots (yes only the volume pots) back and forth quickly then they pop and make that static sound (not the dirty pot sound, yes cleaned all the pots for good measure).  But the electrical discharging sound when you put it back on standby is what gets me, never had that one before.  That was the only reason I had wondered about the choke since everything else has been checked and double checked and even changed multiple times.

Have to say I was kind of dreading coming home knowing this would be back soon to look at.

Thanks for the links (I've trying to collect every link I can and gather the info so I can access it when I'm not online, thank goodness for the huge portable hard drives now).

After I get done with this repair I'm going to take a break and start messing with some builds on my own like I hear everyone else do on here.  Figure will give me a great chance to mess with the circuits and develop that tone I hear in my head that I can't find.

Thanks again to everyone, I hope one day to have answers for others with questions on here like I see everyone else being able to help.

Scott...

[phsyconoodler]

I've got money on the silver mica treble caps.5 bucks.Anyone else in?

[Ryteone]

Will let you know this weekend when I get it back to go over it again.

[Ryteone]

For grins changed out the silver mica caps back to ceramic Dics.  Didn't change.  But I didn't notice I was wrong before stating that when I put my multi-meter probe on certain spots it would cause the DC static on the two volume pots to go away.  It wasn't the probe that was causing it, it was the palm of my hand resting on the chassis!  So I think it has to be some grounding issue now if my hand is filtering the static like that.

Time to dig more!

[Ryteone]

Ok call me dumb or stupid.  I was causing the static.  When I've been testing it I had the knobs off and was rotating the volume pots by the metal post.  When I put the knobs back on and tried it no static sound want so ever.

Now just hunting down that discharge sound when placed on standby.

Sorry for the wild goose chase for the static sounds.  Knew I had been checking all the right parts.  But never had an amp do that like that before (mark that up as another dumb lesson).

Scott..

[LooseChange]

Not so dumb... I spent a few timnes in the early years hunting down something and realized I need to put at least one bolt back on a pot to get anything to work. Or sometimes it's just one bolt on aa pc board to ground the circuit.

IMO, screw the standby!

[jojokeo]

IMO, screw the standby!

+1 - amps w/ SS parts in them do this and it's no big deal.

Even though your "pots w/ static" issue is gone, don't confuse DC on them w/ poor quality or old scratchy pots. This can feel & sound very similar sometimes.