Blues deluxe channel switching problem...fixed.

[TubeGeek]

I have an early Blues Deluxe amp in for servicing.  I read that the wave soldering was done poorly on these amps so I went ahead and re-flowed all solder joints in the amp for good measure.

I replace a stripped input jack, removed and re-installed the 470 ohm 5 watt resistors,  and changed r71 switching resistor from 10k to 100k.  I put the old 470 ohm resistors back in because they both measured good and I don't have any of those resistors in stock...waiting for parts to make it across the border  I did leave more space underneath the resistors this time installing them.  I measure +/- 48V on one side and +/-16V on the other sides of each resistor. From what I have read online these are both very common problems in these amps.

The amp was cutting in and out and crackling while playing, almost like the clean and drive channels were switching automatically.  I was able to fix the problem while chopsticking the amp.  Although when chopsticking the amp, I found at least 4 or 5 areas that if I pressed on would "fix" the problem.  It was at this point I decided to just take the pcb out and go to work.

After reinstalling the pcb and plugging in, the amp has no more nasty noises or switching problems.  Good.  Then I tried switching the channel to clean and nothing happens when I press the drive select switch.  I thought that maybe the 10k I replaced with 100k was the problem so I switched r71 back to the 10k value.  It didn't fix the switching problem.  I'm thinking it could be faulty relays or a faulty opamp???  Looks like I need to do some voltage checks...I'll work on it tomorrow night after work.

I read that often fixing one problem reveals another problem in these amps.  What would be the next thing you'd troubleshoot for switching in this circuit?

Any help will be appreciated.  I wanna get this off the bench so I can work on something more fun.

http://www.el34world.com/charts/Schematics/files/fender/BLUES_DELUXE.pdf

[sluckey]

1. Verify that +16V power supply is OK.

2. Does LD1 turn on and off? If not, check for proper voltages on U3 pins 4 and 8. If voltages good, replace U3. If voltages bad, look at the +16V power supply.

3. Check U3-1 and U3-7. Both outputs should toggle between approx. -14V and +14V as you operate the footswitch. If U3-1 does not toggle, look at U3-2. If U3-2 toggles above and below +.6V, replace U3. If it doesn't toggle, look at components between footswitch and U3-2. U4-7 should toggle also, but it doesn't drive a relay.

4. If all op amp outputs are toggling as expected, look at the relay coils and associated components (R74, CR12, C31 for RY2 and R72, CR11, C30 for RY1). Pin 1 of each relay should toggle between -14V and +14V. You may be able to hear or feel a click as the relay energizes (TIP... Use a long handle screwdriver. Put the tip on the relay case. Put your ear on the end of the handle.). The resistance of the relay coil is probably a few hundred ohms. Open circuit is definitely bad.

[ThermionicEngine]

If I had to pick one amp that I see on my bench the most it would be the blues/Hot Rod Deluxe.  Might be a function of the number produced but I scarcely can go a month without getting one in the shop.  If the manufacturer would upgrade a few parts and a couple of minor mods, these would be good affordable tube amps.  Sluckey, as usual, has given you the best advice.  I would follow the same TS path.  I only add that I have had to replace several selector switches or re-solder them to the PCB.  If the owner doesn't use the footswitch, the panel switch is, like the 1/4 inch jacks, a weak point in the design.  Also, replace the 470 Ohm 5 Watts even if your multimeter says their value is good.  Mount the new ones as you did the originals- off the board.  Other issues, if it is still not right, look for lifted/broken traces.  Maybe a '65 Vibrolux Reverb will come in next...

[phsyconoodler]

The LED will not come on if the foot switch jack is sprung either.Don't overlook that.

[LooseChange]

If the switching circuit is disabled the amp will stay in the distortion mode.

We all get lots of these on our benches.

Those traces around the 470r resistors get really brittle and lift due to all the heat. Check the continuity between parts that should be connected by the traces.

I have done many point to point fixes due to lifted traces.

[ThermionicEngine]

Amen, Loose Change.  I looked in my queue and there is a Blues Deville...  I had 2 HR Deluxes in March. I'm not looking back any further- I'll need therapy...
Larry

[rafe]

check the diodes there was a problem with those failing too

[TubeGeek]

Update...

really dumb question...do I need the footswitch to change channels?  I assumed the channels could be changed via the drive select switch.  I do not have a footswitch with this amp.

2. Does LD1 turn on and off? If not, check for proper voltages on U3 pins 4 and 8. If voltages good, replace U3. If voltages bad, look at the +16V power supply.  NO, the led stays red.  U3 pin 4= -16.8, pin 8= 0


3. Check U3-1 and U3-7. Both outputs should toggle between approx. -14V and +14V as you operate the footswitch. If U3-1 does not toggle, look at U3-2. If U3-2 toggles above and below +.6V, replace U3. If it doesn't toggle, look at components between footswitch and U3-2. U4-7 should toggle also, but it doesn't drive a relay.U3 pin 1= +13.91 pin 2= 0.140 pin 7= 0. Voltages aren't toggling with drive select switch engaged

I can't hear the relays switching at all.

cr12 anode vdc= -16.8, cathode= +9.2

cr11 anode= -16.8, cathode= -14.43

I thought it may be the 4560 dual opamp so I removed the chip and installed a socket.  I installed a 4558 just to see what happened.  It didn't help.

I'm still stuck on this one.

[sluckey]

U3 pin 4= -16.8, pin 8= 0

Big clue... Pin 8 should be +16v. Looks like the +16v power supply is dead. Check CR20, C38, R85, CR22, and C43.

[TubeGeek]

cr20 cathode measures +50vdc
r85 measures +48 on one side and +16 on the other side
cr22 cathode measures +16 vdc
c38 measures +48 vdc across it
c43 measures +16 vdc across it

The schematic is saying cr20 cathode should be 32.8vdc at that point.  I've got +48 to 50 vdc there.  The difference is 16v...hmmm

I swapped out the 4560 dual opamp with another dual opamp I have which is a 4558.  I can't see a reason why this chip wouldn't work in the circuit but I certainly could be overlooking something important.

It seems that the 16v supply is functional doesn't it?  I do measure +16 and -16 off of the 470ohm resistors and elsewhere in the circuit.  I just don't get it at pin 8. 

Do you recommend ordering a new 4560 and testing again?

[phsyconoodler]

No,you are losing the 16v supply 'before' it gets to the IC.Find the offending path first.

[phsyconoodler]

Aso when Sluckey says check those points,he means check the values to make sure they measure correctly.You cannot check a capacitor while it is still in the circuit.The resistors should be ok.

[sluckey]

Sounds like the PS is good, but the +16 is not getting to the IC. Do a resistance check... Drain C43 first, then check resistance between C43 positive end and U3-8. Should be zero ohms. If not, look for broken trace, bad connector,  bad jumper, etc. If U3 is on the same board as C43, there should be a straight (maybe some twists and turns) path between the two. Since you have installed a socket for U3 just pop the IC out until you have +16 at pin 8.

[TubeGeek]

Removed c43 and c38...measured capacitance value...both caps good.

Inspected pcb traces carefully, no signs of lifted traces. Also cleaned flux from pcb just for good measure.

Resistance between pin 8 and + of c43 is zero.

Still no +16vdc on U3-8.

The only thing I can think of next is the relay is toast.  I suspect this because comparing cr12 to cr11, i measure -16 on the anode of cr12 and +9 vdc on the cathode of cr12.  On cr11's anode I measure -16 and on the cathode I measure -14.  My idea is to replace both cr12 and the relay???

[sluckey]

Let me pull some info together. You said...

c43 measures +16 vdc across it

Resistance between pin 8 and + of c43 is zero.

Still no +16vdc on U3-8.

How can that be? Do you measure +16v from C43 positive terminal to chassis? What voltage do you measure on U4-8?

I really don't suspect CR12 or the relay but here's an easy way to eliminate them... Lift one leg of R74 and R72. This removes both relays from U3A and U3B outputs. Now just concentrate on making the LED turn on and off. Does it?

[TubeGeek]

Yeah I correct myself... I measured 16vdc from chassis to positive of c43.

I measure -10.3 vdc on u4-8.

Lifted both r72 and r74. The led doesn't change when the drive select switch is pressed.

[sluckey]

Hmmm, U3-8 is 0v, U4-8 is -10.3v (that's what I'd expect on pin 5), and C43 positive terminal is +16v. All three of those points are tied together and should be the same voltage. Surely you're counting the pins correctly? If so, you have broken traces or some voodoo problem! Check for zero ohms between all three of those points. Here's a dip chip pin layout just to be sure we're talking about the same pins.

EDIT... See if you can find +16V on ANY pin of U3 and U4.

[TubeGeek]

Oh crap I feel like a dolt.

I've been reading the pinout wrong.

 

U3:
1: 13.74
2: 0.067
3: 0.768
4: -16
5: 0
6: 0
7: -15
8: 16

U4:
1: -15
2: 0
3: -14
4: -16
5: -10
6: -0.155
7: -15
8: 16

[sluckey]

I've been reading the pinout wrong.

OK Alice. That rabbit got away!   

Let's start over. But first, a couple questions. Why did you originally replace R71 with a 10K? In the pinout confusion is it possible that you have had U3 plugged in backwards at some time? If so, replace it with a fresh chip. I'd love to see a closeup pic of U3 and surrounding board area.

Let's concentrate on just making the LED work. Disable the relays by lifting one leg of R72 and R74 and leave them disconnected until the LED works. Let's deal strictly with U3A. I need to know the voltages on pin 2 and pin 1 with switch on and off. Four readings in all. The voltage on pin 2 may not change much so be accurate.

[TubeGeek]

When I began working on the amp I did a search online to see what problems were common with these amps.  I knew these amps are known for several problems.  The reason I initially changed the value of r71 from 10k to 100k was because I read in multiple forums that fender released a tech note saying to replace it.  TN95-5  was the tech note.  As of now the resistor value is back to the stock 10k value.

http://music-electronics-forum.com/t16817/

It's doubtful that I installed the chip incorrectly.  I may not have been reading pins correctly but I am sure I didn't install it incorrectly.

Switch off/out:
pin 1) 0.067 vdc
pin 2) 14.71

Switch on/in:
pin 1) 0.067
pin 2) 14.83

[sluckey]

Switch off/out:
pin 1) 0.067 vdc
pin 2) 14.71

Switch on/in:
pin 1) 0.067
pin 2) 14.83

You have the numbers for pin 1 and 2 reversed, but that's OK. Pin 2 should be the little numbers and it ain't changing, so the problem should be between the footswitch jack and pin 2. There ain't much. Make a couple more voltage readings.

1. Measure voltage at anode of CR7 (switch on and off).

2. Measure voltage at junction of R59 and R60 (switch on and off).

If the above readings don't change with the switch, try this... Just stick a standard phone plug in the footswitch jack to isolate CR5, CR6, and the Drive Select switch. Does the LED turn off?

Can you stick around this morning to troubleshoot this?

[TubeGeek]

anode of cr7= -0.001...switch on and off makes no difference in voltage

junction of r59 and r60= -0.001 same thing...switch does not change voltage

I replaced the footswitch jack...didn't help, plugged in a 1/4" plug, LED does not change.

[sluckey]

Look at this simplified drawing. This is what you have when you insert in a blank plug into the fs jack. Put the plug in now. I left out C27 and C28 but if either of these are shorted the circuit won't work.  R59, R60, and R61 form a simple voltage divider across 38VAC. Check the voltages. Check the resistors. Check CR7. Make sure nothing is shorted to ground that ain't supposed to be.

[TubeGeek]

Checked the resistors r59, r60 and r61...they all measure close to spec.

I cannot find any shorts to ground.

How do I measure the ac voltage?

[sluckey]

Set your meter to AC scale. Don't you have a Fluke? Maybe even auto ranging? That 38VAC at the top of the divider comes straight from the power transformer. The voltages I wrote on the simplified schematic are what you should see with a blank plug inserted into the FS jack. I think you're very close to solving this.

[TubeGeek]

OK, I'll continue on...thanks for the help.  I was ready to pass this one off.  My brain seems to be in another dimension, been zapped too much I guess.

Measured from the PT cp16 to both sides of r59 and r60 and get 39.9 VAC.

Measured from cp16 to the anode of cr7 and get the same 39.9 VAC.

[TubeGeek]

Ok so I found the dang problem.  The pcb trace lifted off of cp16 and was not connecting to r59.  

It was not easy to find.  Once I thought over what Steve has been advising, it had to be around that area so I very closely inspected the traces and it wasn't noticeable to the eye but I did not measure continuity from(power tranny 28 vac tap) cp16 to r59.  I thought, this has to be it so I tacked in a jumper and powered up...holy $%#@ it freakin works!

This is probably the third or fourth pcb amp I agreed to work on and boy I tell ya, I don't enjoy the problems they have. Such a little simple problem threw me for a huge loop.

Thanks to all of you for the advice and especially Steve for really diggin in to help.  Funny how you guys even told me it could be a lifted pad.  I swear I really really did look the amp over many times!  
 

[LooseChange]

Since I work on a lot of these I've been keeping an eye on the progress...
Nice job. There is a learning curve to everything.

Sluckey you are he man for sticking with it.

From my experience... Trace the circuit by checking continuity from one component lead to another.

[TubeGeek]

The part that made it hard to find was that the soldermask did not show any signs of any problems.  The trace had a tiny break in it, underneath the mask.  It was not evident by just looking at it.  The only way to confirm was with the meter. 

I'm also a little out of shape with troubleshooting.  I took a long break from amp work and am getting back to it these days. 

Feels good to get it done though.

[Tone Junkie]

Thanks for sharing with us TubeGeek I have learned alot about trouble shooting lately from these type of threads and every ones hard fought battles in finding these things.
I learn something everyday from this forum and enjoy every minute of it.
Thanks guys Bill

[jjasilli]

Ditto to all that!  Good job Tone Junkie!

[ThermionicEngine]

Ok so I found the dang problem.  The pcb trace lifted off of cp16 and was not connecting to r59.  

It was not easy to find.  Once I thought over what Steve has been advising, it had to be around that area so I very closely inspected the traces and it wasn't noticeable to the eye but I did not measure continuity from(power tranny 28 vac tap) cp16 to r59.  I thought, this has to be it so I tacked in a jumper and powered up...holy $%#@ it freakin works!

This is probably the third or fourth pcb amp I agreed to work on and boy I tell ya, I don't enjoy the problems they have. Such a little simple problem threw me for a huge loop.

Thanks to all of you for the advice and especially Steve for really diggin in to help.  Funny how you guys even told me it could be a lifted pad.  I swear I really really did look the amp over many times!  
 

I ducked out for a bit to work on some backlog.  Glad to see it worked out.  Hats off to Steve, again.  Some manufacturers' PCBs are just SOBs... Allbest- Larry

[plexi50]

The part that made it hard to find was that the soldermask did not show any signs of any problems.  The trace had a tiny break in it, underneath the mask.  It was not evident by just looking at it.  The only way to confirm was with the meter.  

I'm also a little out of shape with troubleshooting.  I took a long break from amp work and am getting back to it these days.  

Feels good to get it done though.

Great thread. I use a camera and take pics of a PCB  board from all angles. You may be amazed at what the PCB board soldering looks like on a computer screen with high res pics. I find all kinds of cracks and near unsoldered tube pins that i could not see with my naked eye. I repaired a DeVille yesterday that had 3 of it's PS caps just flopping around and no longer soldered at all. How it worked at all i dont know other than the cap leads were slightly touching the PCB board trace and arching over during operation. The solder amount used for the power tube pins is vey minimal. I also find that the heater filiments pins on the power tubes come loose and the amp drops it's volume intermittantly loosing power when one tube drops out for a second or more.