VCA testing as described in the fabrication manual results in the desired output on VR7 (rightmost pin) when the gate is connected to R146, however it does not decay, which is what I think it should do.
I tested the BA6110 as described here: http://wiki.jonnay.net/x0x/vcatesting
My pin 4 shows 1.0v when gate is not present and 1.2v when gate is present, although my scope isnt calibrated so im just guessing. It goes up very slightly when the gate is connected.
Pin 9 shows 12v at all times, gate or no gate.
Anyone else run into this? Could it be another bad batch of BA6110s? I don't know what the actual problems were with the other date code.
I probably have a solder bridge somewhere that I haven't tracked down yet ;P
BA6110 oddities
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Please be positive and constructive with your questions and comments.
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- Posts: 19
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Ok I found a problem, I forgot a capacitor (I think it was C41). Now it appears as though the envelope effects the VCA, but it doesn't appear to go completely silent.
I misunderstood what pin 9 is supposed to show. It should always be 12v regardless of gate.
Either way that pin 4 oddity is still present even after I put in the missing cap. With no gate the voltage at pin 4 is 1.017 and with gate is 1.133. I suspect this is why the VCA doesn't go completely silent.
I went through and ensured that every part I've put in so far is in there correctly. I went over all the solder points again and have checked for solder bridges.
I misunderstood what pin 9 is supposed to show. It should always be 12v regardless of gate.
Either way that pin 4 oddity is still present even after I put in the missing cap. With no gate the voltage at pin 4 is 1.017 and with gate is 1.133. I suspect this is why the VCA doesn't go completely silent.
I went through and ensured that every part I've put in so far is in there correctly. I went over all the solder points again and have checked for solder bridges.
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- Joined: Fri Feb 17, 2006 5:35 am
that is good
can you check the voltage at
the juncture of d27 an q3
it should be 0v with no gate present
if it is 0v
then there is most likely a problem with
q1 q2 q3 or q4
you can test this by removing q1
if the vca still doesnt go quiet
than there is a problem with the vca
or the trace to pin4 has some slight
conductance to a higher potential
you can hit the solder joint with some solder wick
and deflux the area and see if that helps
can you check the voltage at
the juncture of d27 an q3
it should be 0v with no gate present
if it is 0v
then there is most likely a problem with
q1 q2 q3 or q4
you can test this by removing q1
if the vca still doesnt go quiet
than there is a problem with the vca
or the trace to pin4 has some slight
conductance to a higher potential
you can hit the solder joint with some solder wick
and deflux the area and see if that helps
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- Posts: 19
- Joined: Tue Feb 14, 2006 9:25 pm
At junction D27 - Q3 the voltage is 0.45v with no gate and 0.56v with gate.
Additional tests:
Q32 - R132 junction with no gate is 1.7v with gate is 0.14v
R132 - Q31 junction with no gate is 1.8v with gate is 0.14v
Q31 - R131 junction with no gate is 2.2v with gate is 0.69v
Does this mean my problem is somewhere between D27 and D35/D36?
Additional tests:
Q32 - R132 junction with no gate is 1.7v with gate is 0.14v
R132 - Q31 junction with no gate is 1.8v with gate is 0.14v
Q31 - R131 junction with no gate is 2.2v with gate is 0.69v
Does this mean my problem is somewhere between D27 and D35/D36?
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- Posts: 19
- Joined: Tue Feb 14, 2006 9:25 pm
Q31 wasn't in backwards, but I removed it. Now pin 4 of the BA6110 with no gate is 0.998v and with gate is 1.004v.
Now when I test the output of the VCA (at the rightmost pin of the volume) I see about 18mV of ripple when i have all of the knobs (except tune and volume since its not installed) turned fully clockwise.
So the VCA is now nearly silent with no gate, but it's control input (pin 4) is still not at the right voltage. Also when I connect the gate, the VCA voltage peaks and then decays as expected.
Should I try a different 733 in Q31 or is there something else that's the problem?
Now when I test the output of the VCA (at the rightmost pin of the volume) I see about 18mV of ripple when i have all of the knobs (except tune and volume since its not installed) turned fully clockwise.
So the VCA is now nearly silent with no gate, but it's control input (pin 4) is still not at the right voltage. Also when I connect the gate, the VCA voltage peaks and then decays as expected.
Should I try a different 733 in Q31 or is there something else that's the problem?
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- Posts: 19
- Joined: Tue Feb 14, 2006 9:25 pm
ok I removed D27 and the voltage at pin 4 on the BA6110 is still around 1v regardless of gate. Although the voltage on pin 4 was not right before I removed D27 (but had Q31 removed) the output (measured at the rightmost pin of VR8) seemed to be nearly correct. It jumped up when the gate was applied and decayed until the ripple was around 18mV. Another oddity that I notice is that the DC offset of the right pin on VR8 drifts when i connect my meter or scope. It drifts faster with my meter. I suspect this has something to do with the load of my meter/scope affecting the opamp.
So since it seemed to be close to working without Q31, but with D27.. what does Q31 do?
I don't think Q31 was bad because after I removed it I tested it and it had a beta of 269. However the ECB seems backwards from the data sheet...
So since it seemed to be close to working without Q31, but with D27.. what does Q31 do?
I don't think Q31 was bad because after I removed it I tested it and it had a beta of 269. However the ECB seems backwards from the data sheet...
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- Posts: 3155
- Joined: Fri Feb 17, 2006 5:35 am
q31 controlls the current into the vca
if its pinout is somehow backwards
that would definitely make it not work
although id be suprised if only one of the
transistors you recieved was faulty
in that particular way
although 28mv of signal doesnt seem like much
you will still probably be able to hear it in your mixes
id suggest pulling q1 and seeing what the pin4 voltage does
you can also check the trace from pin4 to q1
it might have a small short someplace
or perhaps there is an excess of flux or solder
the smallest current into that pin can turn the vca on
if its pinout is somehow backwards
that would definitely make it not work
although id be suprised if only one of the
transistors you recieved was faulty
in that particular way
although 28mv of signal doesnt seem like much
you will still probably be able to hear it in your mixes
id suggest pulling q1 and seeing what the pin4 voltage does
you can also check the trace from pin4 to q1
it might have a small short someplace
or perhaps there is an excess of flux or solder
the smallest current into that pin can turn the vca on
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- Posts: 19
- Joined: Tue Feb 14, 2006 9:25 pm
you are right in that Q31 wasn't the only transistor with a pinout that is backwards from the datasheet. All of the 733s are backwards from the datasheet, but I assumed that the image on the x0xb0x pcb is showing the correct orientation as that is how I put them in and everything tests correctly up to the VCA.
If I'm reading the schematic right, the signal going into pin 4 on the VCA can be traced back to D27 and Q31 and prior to that the signal to Q31 can be traced as far back as D35 and D36. The signals at D35 and D36 are correct. So if I replace Q1 and Q31 and leave out D27, yet I still have odd values at pin 4 on the VCA this would lead me to believe that the issue is between D35/D36 and Q1. Is my thinking correct?
If I'm reading the schematic right, the signal going into pin 4 on the VCA can be traced back to D27 and Q31 and prior to that the signal to Q31 can be traced as far back as D35 and D36. The signals at D35 and D36 are correct. So if I replace Q1 and Q31 and leave out D27, yet I still have odd values at pin 4 on the VCA this would lead me to believe that the issue is between D35/D36 and Q1. Is my thinking correct?
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- Posts: 12151
- Joined: Thu Apr 06, 2006 4:21 pm
yeah theres this wierd thing where some 733s are not the same pinout. this was a problem when we first started because i trusted the datasheet
but the x0xb0x schematic and board work with the transistors you've got..the 2sa733s are from mouser so maybe they have a datasheet up. i think fairchild makes them?
but the x0xb0x schematic and board work with the transistors you've got..the 2sa733s are from mouser so maybe they have a datasheet up. i think fairchild makes them?
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- Posts: 19
- Joined: Tue Feb 14, 2006 9:25 pm
Please be positive and constructive with your questions and comments.