I think where you said preamp in jack, you meant power amp in?
You may still have an issue with the power amp in jack, give it another shot of cleaner and work a cord in and out of the jack several times.
See if it makes a difference.  If not, try connecting preamp out jack to power amp in jack with a patch cord.  Then try playing through the regular input again.

  Stick with 1458's and see if it improves reliability.
Normally 4558 is ok to sub for 1458.  However, there are odd cases where they don't work well, and if I'm remembering correctly, the only place they seem to have issues is in some Marshall amps.  I can't remember which models or why it is a problem.  I think I have seen Enzo mention the same issue and he may remember more details.

  If the ripple is so low that a good meter will not accurately measure it, then it is not a concern. 
Yes, it is nice to be able to see it on a scope, but if there really is a problem, it should show up on the meter as AC volts.

  Yes, 100nF and 47nF.  They should also have a voltage marked on them.  Do not use them in a circuit that will exceed the voltage rating.

The value is in between the letters, so 473 and 104 for those.
The first 2 digits are significant, the 3rd digit is the multiplyer, giving the value in pico-farads.  So for the multiplyer, add that many zeros to the significant digits.
So in this case, 47000, and 100000 pico-farads.
To convert to nanofarads, move decimal place 3 digits to the left.  You get 47 and 100 nano.
To convert to microfarads, you move decimal place 6 digits to the left (from pico).
So .047 and .1 microfarads.

Quote from: Roly on May 20, 2014, 02:30:39 PM
Quite likely not;

Title: GFX120a
No: 07S252-XX
Sheet: 1 of 2
Date: 6/19/98

The basic point is that one has extra bypassing the other doesn't, and this change in DSP supply arrangement may be a clue they were having some problems in this area.

Yes, that is the same drawing I have.  It's a 470 ohm (R88), not 47.
It is used as a voltage dropper because they are tapping off the +40V supply.  The other circuit has it's own winding and rectifier for a separate supply and has a 10R resistor.
I'm not arguing that the .1uf bypass cap may help, I just wanted to point out that the supply circuits are quite different and the 470R is not just for filtering.

Agree to try the .1 bypass as close to the DSP chip as you can and see if it helps!

 Roly, the schem. with the 10 ohm has its own supply, not running off the 40V line.
The gfx212 schem. shows a different supply and 470, not 47 ohm.  Are we looking at the same schematics?

Quote from: smackoj on May 13, 2014, 07:31:29 PM
Ola amigos; I have a Lab Series L7 which I am pretty sure is the same amp with 4 ten inch spkrs instead of 2 twelves. I can only get normal volume using one low gain input.

First, the inputs are labelled different than what we normally see, HI means for high output pickup, so there is less gain with the HI inputs.  The LO inputs will give more gain.
Each pair of inputs goes to same IC.  So for your channel that has 1 input working, the other input must have a problem with the jack or solder.  If a channel input IC is bad, neither jack for that channel will work.
  So you may have a few separate problems here.

Quote from: Brhibler1 on May 13, 2014, 05:11:08 PM

Quote from: g1 on May 13, 2014, 03:56:55 PM
  Put a patch cord between preamp out and power amp in (dry), any difference?

That had already been checked. I'm an experience amp tech, 

lol, that post was supposed to have gone here: http://www.ssguitar.com/index.php?topic=3472.msg25990#msg25990
Sorry about that, you must have been scratching your head wondering why I would think the loop could cause that and what the "dry" was about. 
I would have thought the lf351 ok as a lf356 sub, but, as you say, maybe it was defective. 
  Or maybe someone else here more familiar with the circuit will comment on whether there is a problem using the lf351 in this spot of the circuit.

  Put a patch cord between preamp out and power amp in (dry), any difference?

Edit:  This post was supposed to go in here: http://www.ssguitar.com/index.php?topic=3472.msg25990#msg25990
Sorry for any confusion.

  Couldn't find any free schematics, but available for sale here:
http://www.hansenguitars.com/engine/inspect.asp?Item=422&Filter=Amps

Quote from: Roly on May 02, 2014, 02:20:16 AM
Another odd fault that old Fenders can exhibit when the electros are going down is that the volume goes down to zero at about 1 or 2 on the knob, then comes back up again from there to zero.

Roly, which electrolytics cause this, cathode bypass caps or supply filters?

  Excellent point Dr.Gonz.  I don't know if the ads here are enough to cover Joe's costs to keep the place running.  If he wanted to put on a "donate" button or run a fundraising drive, I'd be more than happy to donate, this site is greatly appreciated!

  Blending is not possible.
Switching is only easy if you turn off both amps.  Otherwise you need a fairly sophisticated switching box that makes absolutely sure the first amp is disconnected before the second is connected.
  Both amps connected to the same load at the same time usually ends in smoke, flames, and tears.

  Well, the only good news is I tried to buy the domain name through the godaddy link and it said the "domain is not available".
Dr.Gonz, thanks for the reminder about the paypal thing.  In case it's a financial issue I sent a donation via paypal to paypal (at symbol) firebottle.com.  Those donations are accompanied by an email to him titled "you've got money" so I think he will have it set up so those don't go into his spam folder  .  Added a note about hoping to see the site back up, so if he was unaware of the issue he should be notified now.