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The Fisher X100 - Right Channel Out

Tim D said:
Instead I'd try swapping the small signal tubes from left to right channel (with the jumper removed). That's very easy to do. Just need to verify if the problem stays on the same channel or moves with the tubes.

Have you had the tubes tested?
Click to expand...

I don't have a tube tester. I've swapped tubes back and forth. I'm not sure which is signal tube? The preamp tube 12AX7? Or Phase Inv. 7247? I've noticed that only one 7247 has a short, bursting glow when I turn the unit on.
 
Dig22 said:
I don't have a tube tester. I've swapped tubes back and forth. I'm not sure which is signal tube? The preamp tube 12AX7? Or Phase Inv. 7247? I've noticed that only one 7247 has a short, bursting glow when I turn the unit on.
Click to expand...

Looking at your schematic, the small signal tubes are:

V1 (Preamp Channel A), V6 (Preamp Channel B)
V2 (Audio Frequency Amp Channel A), V7 (Audio Frequency Amp Channel B)

The other tubes were all verified when you used the jumper and said both channels were passing sound.

So,

1. remove the jumper from the volume control wipers if you haven't already done that.
2. then swap V1 and V6 with each other and also swap V2 and V7 with each other and
3. try again to see if the problem remains on the same channel or moves to the other channel.

If the problem moves to the other channel then you need to look at replacing one or two tubes (that you just moved) on that channel. If it doesn't move and stays on the same channel then the search gets more involved.
 
BTW, if you add your location to your avatar you might get a nearby AK member to test your tubes for you. My avatar shows I'm in Melbourne Florida. There is a thread somewhere where AK members post that they have tube testers and their locations that might also help.
 
Dig22 said:
I don't have a tube tester. I've swapped tubes back and forth. I'm not sure which is signal tube? The preamp tube 12AX7? Or Phase Inv. 7247? I've noticed that only one 7247 has a short, bursting glow when I turn the unit on.
Click to expand...

The short bursting glow is often called the "Mullard Flash". The filaments seem to glow brightly for a fraction of a second before they heat up and the resistance settles. This is most often reported for Mullard branded tubes, but I've heard others report the phenomenon on non-Mullard tubes too. Just a fun fact.
 
Tim D said:
Looking at your schematic, the small signal tubes are:

V1 (Preamp Channel A), V6 (Preamp Channel B)
V2 (Audio Frequency Amp Channel A), V7 (Audio Frequency Amp Channel B)

The other tubes were all verified when you used the jumper and said both channels were passing sound.

So,

1. remove the jumper from the volume control wipers if you haven't already done that.
2. then swap V1 and V6 with each other and also swap V2 and V7 with each other and
3. try again to see if the problem remains on the same channel or moves to the other channel.

If the problem moves to the other channel then you need to look at replacing one or two tubes (that you just moved) on that channel. If it doesn't move and stays on the same channel then the search gets more involved.
Click to expand...

I swapped tubes V1 & V6 / V2. & V7. Same problem with right channel. Is it possible it's in the Volume Control?
 
Dig22 said:
I swapped tubes V1 & V6 / V2. & V7. Same problem with right channel. Is it possible it's in the Volume Control?
Click to expand...

Remote possibility that it's in the volume control, but I would be looking elsewhere because you jumpered the wipers on the volume control and it was working out of both channels.

So it does this on Aux inputs? (If you are testing with phono my following inputs will be different.) If so that reduces the problem to between the V2 and the volume control on the right channel. If it does this on Aux input, I would next be measuring voltages on V2 and V7 and comparing that you are getting the same voltages to ground on all the pins on both tubes. Knowing what those voltages are may tell a story. Just make sure you are comfortable with doing those measurements safely as the voltages are dangerously high. If you aren't comfortable measuring the high voltages safely then find someone who is. Be careful to only touch the points you intend as bridging between points with high voltage with a probe can break stuff and the arc and sound will scare you too.

Often a socket may be bad or have a loose or corroded connection (and that voltage comparison between channels might uncover this.) You could try cleaning the V2 socket and making sure the leaves are making good contact. I use dental tools or jewelers screw drivers to retension the sockets. Just be delicate.
 
To minimize the meter probe shorting across close points tape the probe (or better heatshrink) all but the very tip of the metal part of the probe. This will minimize sparks, smoke, stripes in scivvies, and LOUD and prolonged verbiage that in some younger circles would be inappropriate at best. Aw hell, your my age.....go ahead and cuss a blue streak!
 
larryderouin said:
To minimize the meter probe shorting across close points tape the probe (or better heatshrink) all but the very tip of the metal part of the probe. This will minimize sparks, smoke, stripes in scivvies, and LOUD and prolonged verbiage that in some younger circles would be inappropriate at best. Aw hell, your my age.....go ahead and cuss a blue streak!
Click to expand...

Thanks Larry. I taped my probes. Almost sounds like a song title....
 
Tim D said:
Remote possibility that it's in the volume control, but I would be looking elsewhere because you jumpered the wipers on the volume control and it was working out of both channels.

So it does this on Aux inputs? (If you are testing with phono my following inputs will be different.) If so that reduces the problem to between the V2 and the volume control on the right channel. If it does this on Aux input, I would next be measuring voltages on V2 and V7 and comparing that you are getting the same voltages to ground on all the pins on both tubes. Knowing what those voltages are may tell a story. Just make sure you are comfortable with doing those measurements safely as the voltages are dangerously high. If you aren't comfortable measuring the high voltages safely then find someone who is. Be careful to only touch the points you intend as bridging between points with high voltage with a probe can break stuff and the arc and sound will scare you too.

Often a socket may be bad or have a loose or corroded connection (and that voltage comparison between channels might uncover this.) You could try cleaning the V2 socket and making sure the leaves are making good contact. I use dental tools or jewelers screw drivers to retension the sockets. Just be delicate.
Click to expand...


Same problem on all inputs - phono, tuner, Aux 1 & 2. Here are voltages:

V2 V7
p1 148.5 p1 159.6
p2 1.2 p2 .6
p3 .94 p3 8.0
p4 .8 p4 10.6
p5 10.56 p5 21.0
p6 148.7 p6 154.3
p7 1.2 p7 .7
p8 1.0 p8 .9
p9 5.5 p9 15.5
 
Dig22 said:
Same problem on all inputs - phono, tuner, Aux 1 & 2. Here are voltages:

V2 V7
p1 148.5 p1 159.6
p2 1.2 p2 .6
p3 .94 p3 8.0
p4 .8 p4 10.6
p5 10.56 p5 21.0
p6 148.7 p6 154.3
p7 1.2 p7 .7
p8 1.0 p8 .9
p9 5.5 p9 15.5
Click to expand...

My nice columns don't look quite the same when I post.. Here they are again....

V2
p1 148.5
p2 1.2
p3 .94
p4 .8
p5 10.56
p6 148.7
p7 1.2
p8 1.0
p9 5.5

V7
p1 159.6
p2 .6
p3 8.0
p4 10.6
p5 21.0
p6 154.3
p7 .7
p8 .9
p9 15.5
 
Dig22 said:
My nice columns don't look quite the same when I post.. Here they are again....

V2
p1 148.5
p2 1.2
p3 .94
p4 .8
p5 10.56
p6 148.7
p7 1.2
p8 1.0
p9 5.5

V7
p1 159.6
p2 .6
p3 8.0
p4 10.6
p5 21.0
p6 154.3
p7 .7
p8 .9
p9 15.5
Click to expand...


The pins 4, 5 and 9 are heater connections and can be ignored as they are in a series string which makes the voltages to ground different (explainable). The pins 1 and 6 are plate connections. The plate voltage values are fine and can be ignored. It's the pin 3 on V2 which concerns me. To bias properly the pin 3 (cathode) should be at a higher voltage than pin 2 (grid) (pins 3 and 2 on V7 are a correct example). I see that the cathode is being powered by a voltage divider circuit fed by the B+ for the tube. The R48 (100k ohm) and R49 (470 ohm) make up that voltage divider. Can you power it down and measure the resistance of both resistors please? You can try it in-circuit so the challenge is to find the resistors. Many resistors can be measured in-circuit. They will be connected to pin 3. While you are in there do the same on pin 3 of V7 for R50 (100k) and R51 (270). Then we can compare the measurements between sides. Also do a basic inspection of the resistors for heat discolorization or burn marks. The color codes are:

100k ohm is (brown black yellow)
270 ohm is (red violet brown)

V2
p2 1.2
p3 .94 <--- Why is this one so different from the voltage on V7? Maybe R48 or R49 is bad?
p7 1.2
p8 1.0

V7
p2 .6
p3 8.0
p7 .7
p8 .9
 
Tim D said:
The pins 4, 5 and 9 are heater connections and can be ignored as they are in a series string which makes the voltages to ground different (explainable). The pins 1 and 6 are plate connections. The plate voltage values are fine and can be ignored. It's the pin 3 on V2 which concerns me. To bias properly the pin 3 (cathode) should be at a higher voltage than pin 2 (grid) (pins 3 and 2 on V7 are a correct example). I see that the cathode is being powered by a voltage divider circuit fed by the B+ for the tube. The R48 (100k ohm) and R49 (470 ohm) make up that voltage divider. Can you power it down and measure the resistance of both resistors please? You can try it in-circuit so the challenge is to find the resistors. Many resistors can be measured in-circuit. They will be connected to pin 3. While you are in there do the same on pin 3 of V7 for R50 (100k) and R51 (270). Then we can compare the measurements between sides. Also do a basic inspection of the resistors for heat discolorization or burn marks. The color codes are:

100k ohm is (brown black yellow)
270 ohm is (red violet brown)

V2
p2 1.2
p3 .94 <--- Why is this one so different from the voltage on V7? Maybe R48 or R49 is bad?
p7 1.2
p8 1.0

V7
p2 .6
p3 8.0
p7 .7
p8 .9
Click to expand...


I think R 48, 49 , 50 , 51 are by section V1 & V6. The values are not 100k or 270 ohm.

on:
V2, p3 R28 is a 100k 1W resistor. I couldn't get a reading. It jumped all over the place
V2, p3 R29 is a 270 ohm resistor. The reading is 263ohm

on:
V7, p3 R66 is a 100k 1W resistor. I couldn't get a reading. It jumped all over the place
V7, p3 R67 is a 270 ohm resistor. The reading 264
 
Dig22 said:
I think R 48, 49 , 50 , 51 are by section V1 & V6. The values are not 100k or 270 ohm.

on:
V2, p3 R28 is a 100k 1W resistor. I couldn't get a reading. It jumped all over the place
V2, p3 R29 is a 270 ohm resistor. The reading is 263ohm

on:
V7, p3 R66 is a 100k 1W resistor. I couldn't get a reading. It jumped all over the place
V7, p3 R67 is a 270 ohm resistor. The reading 264
Click to expand...

Sorry. I'm using the X100 service manual from the AK database.
 
Ok. Had to drop back and look at your schematic pieces in post 6 and it looks like that series re-numbered the resistors as you had indicated. So

V2 - R28 (100k) and R29 (270)

V7 - R66 (100k) and R67 (270)

The measurement jumping around on the 100k ohm resistors might be because of a parallel path. You could try lifting one leg (or replacing with new) the 100k resistors and measure again. Both 270 ohm resistors are good.
 
Tim D said:
Ok. Had to drop back and look at your schematic pieces in post 6 and it looks like that series re-numbered the resistors as you had indicated. So

V2 - R28 (100k) and R29 (270)

V7 - R66 (100k) and R67 (270)

The measurement jumping around on the 100k ohm resistors might be because of a parallel path. You could try lifting one leg (or replacing with new) the 100k resistors and measure again. Both 270 ohm resistors are good.
Click to expand...

I’ve ordered parts and will recap the unit and check/replace resistors. I’ll report back next week.
 
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