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Post subject: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sat Dec 21, 2013 10:43 pm
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Hello all
This is my first post, although I have been reading and learning here for a long time.

I have a 1993 tweed 2x12 blues deville that has almost no volume.
I am comfortable working on amps and discharge capacitors each time before digging in.
Been using homemade audio probe. Recently bought an oscillocope and audio generator, need to learn to use.
I have a schematic for this amp.

Here is a list of what I have tried and what I have done.

1. Installed new f&t filter caps and have a new set of jj tubes.
2. Replaced plastic input jacks with switchcraft.
3. Repaired broken traces and lifted eyelets
4. Checked all resistors and replaced any open or out of spec with schematic
5. Power amp in produces sound so I assume problem is in preamp section
6. No sound from preamp out
7. Checked tube pin voltages and will post them tomorrow
Can someone post what all pin voltages should be for v1 v2 and phase inverter

8. Tried to use fender test points, but can't get millivolts AC to read on multimeter.
9. Yes I have speaker plugged into correct jack
10. I have traced audio through r20 then it stops. R20 tests good. Continuity is good to r22 but no audio there. On schematic they appear to be directly connected or am I reading that wrong?
Anyway, feel like pulling my hair out.
Any help would be very much appreciated


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 2:55 am
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What is the story of the amp ?

Did he play loud before ? Or you just buy it second hand with no test ? You never hear it playing loud before ?

Or it have low volume since you work on it ?

PLEASE ANSWER TO THESE QUESTION FIRST

This amp is not easy to work on for a beginner.

shematic ;

http://support.fender.com/schematics/gu ... ematic.pdf
____________________________________________

You write ;

10. I have traced audio through r20 then it stops. R20 tests good. Continuity is good to r22 but no audio there. On schematic they appear to be directly connected or am I reading that wrong?


Answer ; on schematic they are connected together. If your test are good ( I say IF...) you may have a short after R20 , wich drop signal . Where after R20 ? you have to isolate circuit , disconnect some resistor or check to a short with a meter...

What are your B+ voltages ?


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 9:12 am
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Maybe there is something wrong with RY2B relay sitting right after MASTER volume pot (R21)?


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 9:26 am
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Or " Power Amp In " jack or many many other possibilities........


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 11:14 am
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Thanks for the quick replies
Yes this a very challenging amp, but I am eager and persistent.
I received the amp as part of a trade. The past owner said the amp was "dead" and just stopped one day.

I was just going to post my suspicion about the power amp in jack.
Since this is an interrupting jack, is it possible that it is stuck or broken making the amp think a cord is plugged in. Wouldn't this cut off the whole preamp section?

Also, (which woud agree with the above), I rechecked continuity between r20 and r22. Continuity is there, but then I thought I wonder if it is being grounded, and sure enough, there is continuity to ground. So something is grounding it.

I am now off to go get readings and answer to your original questions.
I will post voltages in a few minutes
I really appreciate the help


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 12:16 pm
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Here are the pin voltages
All vdc

V1
Pin 1. = 263
Pin 2. = .001
Pin 3. = 1.95
Pin 4 = 0
Pin 5 = 0
Pin 6 = 269
Pin 7 = .001
Pin 8 = 1.9
Pin 9 = 0

V2
Pin 1. = 263
Pin 2 = .001
Pin 3 = 1.9
Pin 4 = 0
Pin 5 = 0
Pin 6 = 0
Pin 7 = 0
pin 8 = 0

V3 phase inverter
Pin 1 = 265.5
Pin 2 = cannot measure, get huge pop out of speakers
(Isn't this grid from power amp in?)
Pin 3 = 38
Pin 4 = 0
Pin 5 = 0
Pin 6 = 264.3
Pin 7 = 25 touching produces lowfreq hum(60hz?)
Pin 8 = 38
Pin 9 = 0

V4power

Pin 1 = .011
Pin 2 = 0
Pin 3 = 483
Pin 4 = 484
Pin 5 = -49.9
Pin 6 = .008
Pin 7 = 0
Pin 9 = .014

V5 power

Pin 1 = .004
Pin 2 = 0
Pin 3 = 483
Pin 4 = 483
Pin 5 = -50
Pin 6 = .004
Pin 7 = 0
Pin 8 = .014


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 12:34 pm
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Switch your DVM to the AC volts function and check to see that you've got heater juice to all the bottles. That's pins 4 and 5 in the pre-amp stages, and pins 2 and 7 of your 6L6's.

Arjay

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 12:46 pm
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fretworks,

Which signal path are you tracing, normal or drive? The audio signal follows a different path through the amp depending on the channel selection. You need to pick a channel, trace it's path all the way through, then switch to the other channel. There may be problems with the various switching relays that will show up only when checking the two paths one at a time.

Just noticed Arjay's post. He is right. You have no heater voltage showing on any of the tubes. Note that on the schematic, the voltages in rectangular boxes are DC and the voltages in ovals are AC. Make sure your meter is on the correct scale.

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 12:58 pm
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Heater voltages are

3.2 vac for v1 v2 and v3

V4
Pin 2 = 3.29vac
Pin 7 = 3.25vac

V5
Pin 2 = 3.32vac
Pin 7 = 3.32vac

I can trace audio of both clean and drive up to r20


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 1:29 pm
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fretworks wrote:
Here are the pin voltages
All vdc


V2
Pin 1. = 263
Pin 2 = .001
Pin 3 = 1.9
Pin 4 = 0
Pin 5 = 0
Pin 6 = 0 V2 b Not used
Pin 7 = 0 V2b Not used
pin 8 = 0 V2b Not used



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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 1:32 pm
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All voltage look good , signal path may be broken or short


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 1:43 pm
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You must check with Ohmeter is signal from R 20 pass true Power Amp Jack as I write before and go to C14 .

I see some time amps with low volume because one or some resistor In the Phase Inverter circuit are defective ( V 3 ).

Check R47, R48 , R49, R51, R52. you must desolder one end .

You write in your first post you check all resistors ! If you check without desolder one end at each resistor , test are no good . You must desolder on end .

Check for circuit broken too . Resistor could read good but if printed circuit is broken , good resistor is useless.


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 2:04 pm
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I have confirmed continuity to ground after r20, so am I right to be certain that something is shorting or opened to ground?
Suspects in the direct circuit appear to be r21 master volume which checks OK.
Ry2b which appears to work as it should. How do I further test this?
Power amp in jack. How do I test this?
Q1 how do I test, and can this be removed to see if is the problem?
I am here today working hard on this all day
Thanks again for your help and ideas, I will check through them all.
I am going to drop the top board down again and look at the rear trace from r20 to r22
I am a little worried about the fragilness of the ribbon cables. I have already repaired one lifted trace there.


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 2:12 pm
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On my way now to check those resistors and for and broken traces that i might have missed.
A few days before my first post I found r52 reading open and bad. I replaced that.

I am trying to learn, so when i ask if I test a resistor without unsoldering one leg, and it tests to schematic spec, is that not reliable, or do I always have to unsolder one leg. I understand the effect of a reading when they are in parallel or effected by another component.


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Sun Dec 22, 2013 2:22 pm
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" I have confirmed continuity to ground after r20, so am I right to be certain that something is shorting or opened to ground? ¨

Not good, problem there if continuity is close to "0" or very low ohms. Check also CR2 and CR3 and Q 1 for short or disconnect them if no shure. You may read no continuity or very high ohms reading if they are good or disconnected fron the circuit .

______________________________________________________________________

Disconnect the wire from R20 at J3 pin 4 ( Power amp jack ) and disconnect from C 14 at J3-8 . Connect R20 to C14 . Amp should sound louder if there is problem on J 3 or short there.

Check ohms to ground , must be very high ohms reading .

To test J3 ? ; Disconnet all wire at J3 an read contact as show on schematic


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