I am beginning to think it's switching just fine but something on the boost channel is grounding out and fooking up the signal. Since the clean channel bypasses that part of the circuit it works ok. My issue now is I don't know enough to isolate the boost section on the schematic to troubleshoot. I think I'm seeing channel bleed that is much more pronounced because the boost level is so weak that's why it seemed like it was not switching properly.
4210 tube change gone wrong
- Thread starter vinceB
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The reverb is working and the LED is working. I'll have to check the other stuff tomorrow (wife is in bed so I had to quit). Thanks for your help. I really want to get this going but I understand it's not easy
mickeydg5
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Well according to your voltages at R10 there is something not right in the switching circuit. It may be a bad diode D4, transistor TR1 or both. I am trying to check things and figure it out. I think though whatever may be wrong is affecting Q4 of the CA3046.
To clarify things, we are looking hard at the switching circuit because it is an AC signal grounding system. It provides two direct paths to ground from the BOOST circuit and one for the NORMAL channel, grounding out as you put it.
I should have thought to get you to do this first, but ah.
If you want to try the rest of the amplifier without switching involved do the following:
Remove IC1 CA3046.
Turn BOOST gain and volume to zero. Turn NORMAL volume up. What do you hear?
Now turn NORMAL volume to zero. Turn BOOST gain and volume up. What do you hear?
If the problem is gone and all sounds correct it is a switching problem.
If the problem persist then it is a bad connection, bad component or short somewhere in or at the BOOST circuit.
To clarify things, we are looking hard at the switching circuit because it is an AC signal grounding system. It provides two direct paths to ground from the BOOST circuit and one for the NORMAL channel, grounding out as you put it.
I should have thought to get you to do this first, but ah.
If you want to try the rest of the amplifier without switching involved do the following:
Remove IC1 CA3046.
Turn BOOST gain and volume to zero. Turn NORMAL volume up. What do you hear?
Now turn NORMAL volume to zero. Turn BOOST gain and volume up. What do you hear?
If the problem is gone and all sounds correct it is a switching problem.
If the problem persist then it is a bad connection, bad component or short somewhere in or at the BOOST circuit.
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I pulled the IC and it works on the boost and clean at the same time. I broke the LED lead so I don't know if that works now. It actually sounds kinda bitchin' being able to blend the channels like it is. I'm going to order an IC socket and solder it in next. Like I may have mentioned I am new to this so I'm not sure if using it like it is will hurt it.
mickeydg5
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No, none of this will hurt the amplifier. You are merely modifying or messing with the signal routing by pulling IC1 or preamp tubes.
Whatever happened is a fluke which happened as you were messing with the amplifier and changing preamp tubes. You can come clean. Did you drop a pocket full of change in the amplifier? Joking, ha ha.
Replacing the IC socket may not fix anything. The problem needs to be determined first. You may be creating extra work, way more than necessary by doing stuff like that.
Get a new LED.
Measure the two transistors, TR1 and TR2 as mentioned previously. We will go from there.
Whatever happened is a fluke which happened as you were messing with the amplifier and changing preamp tubes. You can come clean. Did you drop a pocket full of change in the amplifier? Joking, ha ha.
Replacing the IC socket may not fix anything. The problem needs to be determined first. You may be creating extra work, way more than necessary by doing stuff like that.
Get a new LED.
Measure the two transistors, TR1 and TR2 as mentioned previously. We will go from there.
in. I'm going to dive back in this weekend though. Thanks for all the help so far.
mickeydg5
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Ok, that is with plug into INPUT, no footswitch, reverb OFF and amplifier in BOOST mode.
I had to print out a schematic and write notes to keep this stuff straight.
I have to correct myself. You had given 6.3VAC at heaters and 3.8VDC after the switching circuit rectifiers. That seems about right looking at the overall circuit.
The voltage to turn Q4 if IC1 ON is present but it seems to be staying in cutoff mode according to your constant 724mVDC at IC side of R10.
I need you to turn the amplifier OFF and take resistance measurements.
There is a trace that connects the negative side of C41 and C42 to 0V reference. The positive side of those capacitors are on each side of that R10 4.7k resistor.
Place one meter lead at the negative side (leg) of those capacitors and get reisitance measurements to pins #3, #7, #10 and #13 of IC1. We are trying to determine whether these pins and traces are connected properly. Use a CA3046 layout diagram to determine pin locations if necessary. Let me know if you need a link to a datasheet/daigram.
I had to print out a schematic and write notes to keep this stuff straight.
I have to correct myself. You had given 6.3VAC at heaters and 3.8VDC after the switching circuit rectifiers. That seems about right looking at the overall circuit.
The voltage to turn Q4 if IC1 ON is present but it seems to be staying in cutoff mode according to your constant 724mVDC at IC side of R10.
I need you to turn the amplifier OFF and take resistance measurements.
There is a trace that connects the negative side of C41 and C42 to 0V reference. The positive side of those capacitors are on each side of that R10 4.7k resistor.
Place one meter lead at the negative side (leg) of those capacitors and get reisitance measurements to pins #3, #7, #10 and #13 of IC1. We are trying to determine whether these pins and traces are connected properly. Use a CA3046 layout diagram to determine pin locations if necessary. Let me know if you need a link to a datasheet/daigram.
I have not put the IC back in the amp. Do I need to do that before checking resistance at the points you mentioned or are we just checking the traces? The IC was soldered directly onto the board that's why I wanted to throw a socket in there in case I need it in or out for troubleshooting.
mickeydg5
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Ok, refresh my memory. Did you solder the chip socket in place yet?
What matters most at this point is that the .724 VDC you had measured at R10 was with the IC in place. That was my understanding.
If the chip socket is not in place it would be best to wait until it is installed before going forward.
Add
I did not answer the last question in an effort not to get ahead of myself. But everything needs to be checked, not just traces. That is why it is best to have the IC socket in place beforehand.
What matters most at this point is that the .724 VDC you had measured at R10 was with the IC in place. That was my understanding.
If the chip socket is not in place it would be best to wait until it is installed before going forward.
Add
I did not answer the last question in an effort not to get ahead of myself. But everything needs to be checked, not just traces. That is why it is best to have the IC socket in place beforehand.
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Les Moore
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Mickey you kick! Just had to say that
Carry on.
Carry on.
mickeydg5
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I try.
Add
Les, you made me reread, catch and add something. What a help!
Add
Les, you made me reread, catch and add something. What a help!
mickeydg5
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Holy crap but zero resistance at all of those pins is good.
Can you please post a good readable picture of the of the IC1 area for reference?
Can you please post a good readable picture of the of the IC1 area for reference?
mickeydg5
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Ok, all in that picture looks good.
The only way the switching would keep a voltage between R10 and IC1 is if Q4 transistor of the chip were not changing state. When Q4 conducts 0V is left at the bases of Q1, Q2 and Q5 which in effect turns them off allowing the BOOST channel signal to pass through its circuit.
Amplifier turned OFF. Pull up a datasheet on CA3086 for layout. These test checks on Q4 can be done in the socket and pulled. The results should match.
check Q4 of IC1=>
pin #9 = base
pin #10 = emitter
pin #11 = collector
Test resistance with positive probe at pin #9, negative probe at pin #10; = low resistance.
Test resistance with negative probe at pin #9, positive probe at pin #10; = high resistance.
Test resistance with positive probe at pin #11, negative probe at pin #10; = high resistance.
Also test again with the amplifier ON. The voltage .812 at TR1 base pin, that voltage should also be present at the IC1 pin #9 on the chip. The voltage .724 between R10 and IC1, still constant with switching channels?
The only way the switching would keep a voltage between R10 and IC1 is if Q4 transistor of the chip were not changing state. When Q4 conducts 0V is left at the bases of Q1, Q2 and Q5 which in effect turns them off allowing the BOOST channel signal to pass through its circuit.
Amplifier turned OFF. Pull up a datasheet on CA3086 for layout. These test checks on Q4 can be done in the socket and pulled. The results should match.
check Q4 of IC1=>
pin #9 = base
pin #10 = emitter
pin #11 = collector
Test resistance with positive probe at pin #9, negative probe at pin #10; = low resistance.
Test resistance with negative probe at pin #9, positive probe at pin #10; = high resistance.
Test resistance with positive probe at pin #11, negative probe at pin #10; = high resistance.
Also test again with the amplifier ON. The voltage .812 at TR1 base pin, that voltage should also be present at the IC1 pin #9 on the chip. The voltage .724 between R10 and IC1, still constant with switching channels?
mickeydg5
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If you have something plugged into the input and there is a DCV measurement of 0V between R10 and IC1, is the BOOST channel working?
and suddenly it works fine. The only issue now is the LED leads were a dirty and when I soldered it back and its a little flaky. There was clearly a crap connection on the IC and when I soldered the socket it must have fixed it. Thanks for all the help. I have learned quite a bit from this little adventure.
