The ASV is AWESOME (Was: ASV filter problem)

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Post by oozitron » Sat Apr 13, 2019 9:34 am

I am going to try this (for FM of VCO1 by VCO2):

Take VCO2 Saw & VCO2 Pulse from CN5
Send those to an ON-ON switch (to choose the waveform)
Run that through an attenuator pot (B50k)
Output to pin #2 of R67 (which is *not* installed) location
Probably put a 100K resistor after the attenuator

Will this cause any drop in the VCO2 level in the mixer?
Any other things to consider in doing this mod?

Andrew

:hmm: I wonder how FM of VCO1 by the VCO1 SUB wave would sound?
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Post by Synthbuilder » Sun Apr 14, 2019 3:48 am

oozitron wrote:Will this cause any drop in the VCO2 level in the mixer?
No. The mixer takes its inputs from the raw VCO outputs.
Any other things to consider in doing this mod?
It should work fine but make sure the 100K resistor, in between the wiper and the old R62 location, is fitted at the board end of the connection. You may need to use screened cable for the wiper & CCW connection (with the screen connected to the pot's CCW pin and 0V on the main PCB) if you notice any problems with crosstalk when the pot wiper is not at either of its end positions.
I wonder how FM of VCO1 by the VCO1 SUB wave would sound?
Not sure actually. I'll try it today.

Tony

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Post by Leverkusen » Sat Jun 08, 2019 5:52 pm

Eventually I finished my ASV today. Unfortunately I made at least one mistake while building and populated U3 on the pot board with a 550 instead of the 4040-10 so everything was a bit weird on the first power on. :woah:

Since fixing that everything works fine, oscillators, Suboscillator, mixer, envelopes, LFO, VCA and all modulations - except the filter, which behaves in exactly the same way as oozitron experienced: No filtering and unfiltered signal only on HP.

I already swapped out the J201 and the 13700 on the main board with little effect. Also on the pot board I replaced the 1013 and two TL72, also with little effect. Swapping parts seemed to make the signal that gets through the HP clearer - at first it was only audible while turning the resonance knob cw... :hmm:

This is, what I measured after going through this thread:

U10: all pins +14.6V except pin 8 which is +15.2V and 4, which is -15.4V
C32 : +15V
C35 : -15V
Q3 base: +.2V
U14 pin 1 & 16 : 14.6V
Q4: -15.2V to -12.4V w/ freq pot
CN8 pin9 (counted from top?): goes from 8V at freq pot fully ccw to -2.7V at fully cw.
U4 pin1 : -.5V
U4 pin 8 : 15.4V

My first impression is that the ASV sounds pretty nice and I would love to also try the filter...

EDIT: Ah, I am powering it with selfmade adpater connectors from dotcom to MOTM and bridged pins 2 and 3 on both power inlets on the back of the PCB.

EDIT 2: ...also, the Sync switch works in reverse mode - sync is on when the switch is down. You can't place an on-on switch in the wrong direction, can you?

EDIT 3: The last thing I did yesterday was swapping out the J201s. What I did not notice immediately was that this changed the behaviour a bit. Now there is an effect of the filter freq pot on the signal that comes through in HP mode. It does not sound nice but it cuts out the lower frequencies of the mixer signal to some extent now.

EDIT 4: Also after carefully adjusting the filter freq trimmer and the filter freq pot there is an effect on the HP "filtering" from the VC FM1 and VC FM2 now as it would be expected from env1 and the LFO.

I cannot believe that leaving out the 4040 for the 550 in the beginning has damaged so much that swapping part after part makes a bit less worse but not good with every step. :despair:

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Post by Synthbuilder » Sun Jun 09, 2019 4:03 am

Leverkusen wrote:... and populated U3 on the pot board with a 550 instead of the 4040-10 so everything was a bit weird on the first power on.
That would have given you +0.6V and -0.6V reference voltages. I don't think it would have killed anything but stuff would certainly not work well.
No filtering and unfiltered signal only on HP.
From your voltage measurements you have a different problem to Oozitron. I think your problem lies on the main board - the voltages from the pot board seem to be OK. Perhaps the problem is the circuitry around pins 1, 2 and 3 of U6. Resistor values R4, 18 and 19 are crucial to DC stability of the filter, if one of those is wrong weird things will happen.

Also, check that the voltage at the negative end of C35 is around -15V. If not look to see if C35 is the right way around and R80 is 22R.
I am powering it with selfmade adpater connectors from dotcom to MOTM and bridged pins 2 and 3 on both power inlets on the back of the PCB.
Only PSU2 needs to be bridged. PSU1 is already bridged on the board. But shorting pins 2 and 3 on either header shouldn't cause the problems you have.
the Sync switch works in reverse mode - sync is on when the switch is down. You can't place an on-on switch in the wrong direction, can you?
Indeed, you can't. But it is working in the correct direction. Down is supposed to be on because that is the normal behaviour expected in the UK.
Wikipedia (talking about toggle switches) wrote:The direction which represents "on" also varies by country. In the US and Canada, it is usual for the "on" position of a toggle switch to be "up", whereas in many other countries such as the UK, Ireland, Australia, and New Zealand it is "down".
I was reminded of the difference when working on Fender valve (tube) amps. Damn near killed myself when reaching around the back of an exposed amplifier chassis to turn the thing on. :deadbanana:

Tony

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Post by Leverkusen » Sun Jun 09, 2019 11:23 am

Synthbuilder wrote: That would have given you +0.6V and -0.6V reference voltages. I don't think it would have killed anything but stuff would certainly not work well.
Yes, that's what I guessed/hoped too - not in real figures of course...
From your voltage measurements you have a different problem to Oozitron. I think your problem lies on the main board - the voltages from the pot board seem to be OK. Perhaps the problem is the circuitry around pins 1, 2 and 3 of U6. Resistor values R4, 18 and 19 are crucial to DC stability of the filter, if one of those is wrong weird things will happen.

Also, check that the voltage at the negative end of C35 is around -15V. If not look to see if C35 is the right way around and R80 is 22R.
R4, R18 and R19 are all 100K, R80 is 22R and -C35 is -15V.

In my despair I tried swapping the 4558 with a TL072, replaced the 13700 for a second time and reflowed the whole filter section. +/-VREF are both about +/- 10V. Everything around U6 pin 1 - 3 seems to be right to me. :bang:
Down is supposed to be on because that is the normal behaviour expected in the UK.
Wikipedia (talking about toggle switches) wrote:The direction which represents "on" also varies by country. In the US and Canada, it is usual for the "on" position of a toggle switch to be "up", whereas in many other countries such as the UK, Ireland, Australia, and New Zealand it is "down".
Ah, it's a cultural thing then - I thought 'on' would be up to the 'SYNC' inscription. :)

I was reminded of the difference when working on Fender valve (tube) amps. Damn near killed myself when reaching around the back of an exposed amplifier chassis to turn the thing on. :deadbanana:
:woah:

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Post by Synthbuilder » Mon Jun 10, 2019 3:10 am

Perhaps C36 and C37 are wrong or broken. Both should be 330pF.

Remove the LM13700. What is the voltage with respect to 0V at pins 3, 4, 13 and 14?

Tony

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Post by Leverkusen » Mon Jun 10, 2019 5:58 am

Synthbuilder wrote:Perhaps C36 and C37 are wrong or broken. Both should be 330pF.

Remove the LM13700. What is the voltage with respect to 0V at pins 3, 4, 13 and 14?

Tony
Meanwhile I triple checked all parts in the filter circuit and repeated the measurements on the main board without the socket and the pot board attached, with the same results. I also rechecked the whole main boards soldering and found pin9 of one of the other LM13700 unsoldered, which I did not find used in the schematics anyway. Also one pin of the NAND was left out and fixing it increased the quality of the SUB a bit in the direction of less buzzyness.

The only deviation I found in the filter circuit is that you specified CP and CN for the TL072 and since CN are out of production and not in stock anymore at the usual vendors I used ACP throughout as I have lots of them.

I also exchanged C36 and C37. But still no sound and high voltage at U6... :waah:

Without the LM13700 populated I found these values:

pin3 : 7mV
pin4 : 0V
pin13: 0V
pin14 : 33mV

Thank you for the support, Tony!

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Post by Synthbuilder » Mon Jun 10, 2019 8:55 am

Not too sure what to suggest next. We've done the usual suspects and nothing is standing out. The voltages look fine given the faults.

What's the voltage on pin 5 of U14 with the LM13700 inserted? What's the voltage on pin 3 of U10. The pin 3 voltage should be around 1V below that of the pin 5 even if there is a fault elsewhere. If not suspect the J201, Q5. Measure the voltage with a scope probe if you can.

Where did you get the J201? It's an expensive part now and may be fake.

Tony

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Post by Leverkusen » Mon Jun 10, 2019 10:30 am

Hm, I got the J201 from Banzai for 1 EUR per piece. I see now how they are a little more expensive at mouser - at least trying them would bring me over the free shipping mark. Should I also try a new 4558? Or was it sufficient to try temporarily replacing it with a TL072.

Pin 5 of U14 is +15.3V, pin 3 of U10 is +14.6. My scope is a DSO138, I am not sure if it is superior to my handmeter...it's showing 14.9Vavr and 14.3Vavr though, is that still around 1V?

The SUB is at 12Vpp is that intended? It looks good on the scope, like triangle with spike. And it distorts the mixer a bit with all inputs full on. But one could just turn it down a bit and appreciate the possible distortion of course.



EDIT: Deleted the part about the envelope - should have examined it before posting, was an easy fix. Also the part about the Sync - seems that I get confused and should take a run in the park. :doh:

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Post by Synthbuilder » Mon Jun 10, 2019 1:35 pm

Leverkusen wrote:Hm, I got the J201 from Banzai for 1 EUR per piece.
I got some fake MN3005 from Banzai earlier this year. They gave me a refund but I was surprised to see them falling for fake ones. They were pretty obvious fakes too - the old chip identifications had been painted over and new idents laser printed on top.
Should I also try a new 4558? Or was it sufficient to try temporarily replacing it with a TL072.
Ordinarily a TL072 would work fine, so if the only fault was the buffer op-amp subbing a TL072 in there would have made it work. The problem must surely be elsewhere.
Pin 5 of U14 is +15.3V, pin 3 of U10 is +14.6.
The difference seems about right - anything between 0.5V and 1.5V is acceptable - but 15.3V on the output of the LM13700 is significantly higher than what I would expect even under fault conditions. Maybe it is the J201.
The SUB is at 12Vpp is that intended? It looks good on the scope, like triangle with spike. And it distorts the mixer a bit with all inputs full on.
It should be +/-6V, so 12V p-p is fine. It's a little louder because I use a 6V reference to generate the waveform. It works out well because the triangle wave is harmonically less interesting and thus quieter than the saw and square waves.

That said it should not distort the mixer. The gain of the mixer is -0.35, so you shouldn't get a signal any higher than 6V p-p from the output of the mixer even with all the waveforms running full blast. You may get the main output to distort though but this should be able to be turned down with the A_LVL trimmer.

Tony

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Post by Leverkusen » Mon Jun 10, 2019 4:27 pm

So, I soldered two 3pin headers in and tried some J201 I had swapped out and kept in a bag when debugging a project last year. It immediately worked and what a beautiful sounding machine this is! Thanks for all the help and designing this great module. I can see why one could want four of them and a midi interface now. :banana:

Unfortunately this also casts a poor light on Banzai again. Fitting to my last experiences with them though - like selling stuff as in stock that they don't have and also can't get in a reasonable time. :smack:

But I am happy that everything is fine now and if it had not been for those damned JFET's it would have worked pretty well from the beginning, which feels quite good too... :sb:

Though I definitely should learn how these circuits work to be able to make better guesses when something doesn't work! Anything beyond resistors and capacitors still defies me me...not to mention how a filter might work.

Would you elaborate a bit why you specified the two TL072CN and the 4558 for this project? The 4558 seems to be very well-liked in the guitar and stomp-box scene and Banzai have 6 different types of them "in stock". Is it some old-fashioned sound flavour?

Again, Thanks a lot Tony!

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Post by Synthbuilder » Tue Jun 11, 2019 2:49 am

Leverkusen wrote:It immediately worked and what a beautiful sounding machine this is!
Phew! That's a relief.
Unfortunately this also casts a poor light on Banzai again.
Indeed. But do get back to them and explain the problem. You should get your money back and they can check the others that they have for any fakes. Tell them to get them from Mouser - they could probably get some good prices if they buy enough of them.
Would you elaborate a bit why you specified the two TL072CN and the 4558 for this project?
The original SEM filter used 741 single op-amps so a 1458 (dual 741) would have been the most authentic option. But I couldn't bring myself to use such a noisy thing in the ASV so I chose a good sounding bipolar op-amp, the 4558. However, you could use a 1458 in there which does have an advantage over the 4558 and the TL072 in that it doesn't suffer from phase reversal (common mode latch up) when the input signal gets too close to the supply rails. It probably wouldn't sound that different, it's only being used as a voltage follower (amplifier with a gain of one).

The reason the 4558 is offered in so many variants is because of the TS-909 tubescreamer clones. Because the chip is used to clip the guitar signal it is supposed to sound different depending on the manufacturer and the year the chip was made. There may be something in that but in my version of the tubescreamer (overdrive section of the Overdrive-II) I didn't notice much difference between the chips when used with a synth.

Tony

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Post by Pav » Sat Jun 29, 2019 11:20 am

Hi , Reusing this thread to report similar problems on my first ASV build.
I powered up first time today :banana:
I fail the EG test sweeping sustain - no voltage seen.
I also have no filter or main out.

I first thought it might be header three, so built a new ribbon connector - no joy.

vco1,2,sub all ok via mix out.
vco direct outs ok.
key cv fine.
lfo modulating.

- so half a blessing. Like what i hear so far.

I tried patching mixout to filter in - no joy.

off for a cool drink then see if i have same issue as in the thread.
i dread removing the panel again.

So any additional advice to diagnose envelopes welcome.
I used sock board btw.
rgds Pav

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Post by Synthbuilder » Sat Jun 29, 2019 12:25 pm

Pav wrote:I fail the EG test sweeping sustain - no voltage seen.
On both of them? Check you have -5V at pin 6 on both 3310s. If not check U23. The voltage across R109 should not be very big, ie. less than 0.5V.
I also have no filter or main out.
The main out will be quiet if ENV2 is not working. But it would also be dead if the filter is bust. It will be worth going through my recommendations from earlier on in this thread for fault finding on the filter. But get the ADSRs going first.

Tony

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Post by Pav » Sat Jun 29, 2019 1:17 pm

Thanks,I'll report back findings.
rgds Pav

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Post by Pav » Sat Jun 29, 2019 4:05 pm

ok i find voltage across 109 is -11.x and -0.25v output from U23 .. 0.25 also found on pin6 as3310s.
the -5v reg is toast i guess, not sure why.
soldering looks clean, its flatface is as schematic ,C58 C60 have the right values .

ill replace and recheck tomorrow,

oh is it ok to power up just the main board without pot board to check voltage?
rgds Pav

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Post by Synthbuilder » Sun Jun 30, 2019 4:31 am

Pav wrote:ok i find voltage across 109 is -11.x and -0.25v output from U23 .. 0.25 also found on pin6 as3310s.
Firstly double check that R109 is indeed 47R. If it's 47K that would be your problem. If it is correct then pull the 3310s from the board and check pin 6 again. If it goes to 5V then there is a problem with the 3310s or the soldering around them.

The voltage across R109 is determined by the current drawn by the +5V. 11V suggests the 3310s are either drawing too much current or R109 is the wrong value. The 78L05 is probably OK.
oh is it ok to power up just the main board without pot board to check voltage?
Yes.

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Post by Pav » Sun Jun 30, 2019 8:16 am

Many thanks for the spot on advice.
R109 was 4.7k and not 47R . probably the first resistor i put in the board.
Ive checked all the others in the strips and they are 47R so i must have put a loose one back in the bag (slapdash).

So Good News : I now have working EGs and Filter and Main Out. Hurrah

Now i can proceed to calibration. octave spacing is damn good and playable without calibration.

Ill post a picture soon.
rgds Pav

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Post by Synthbuilder » Mon Jul 01, 2019 3:15 am

Pav wrote:So Good News : I now have working EGs and Filter and Main Out.
:banana: :banana: :banana:

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Post by Pav » Mon Jul 01, 2019 1:57 pm

Hi,
calibrating..FOFF1

I have -4.5v to -7v on pin 7 of U10 which from previous comments in the thread is not good. its jumping around a lot. I thought FOFF1 had some effect but now not sure it is

FOFF2 sets pin1 of U10 to 0.0 V fine. voltage fluctuates by 0.02 either way.

I have checked all the resistor values are correct values from VCF_IN_SK to VCF_LP.

My J201s came from Mouser. they have +15v on pin1 as shown. The middle pins have 0.3 and 0.6v (forget which of Q5,Q6 has what.

I will try swapping ICs tomorrow but seems unlikely, then i would move to check soldering.

I do not hear anything that makes me suspect Low Pass filter issue as a result.

Does the BP /Shape select switch have any impact on calibration?
or if shape selected LP or HP.?

and what am i getting when shape selected and pot is half way between LP & HP:hmm:
rgds Pav

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Post by Pav » Mon Jul 01, 2019 2:10 pm

I have noticed an odd burst of noise when playing a particular note above C4
..and ive tracked it down to the sub oscillator going into distortion presumably at a particular frequency. If I back off the sub oscillator using the mixer - it goes away. It does not happen playing below C4. And s not there when i play one key above or below the offending note.

Should we even expect sub oscillator to span 0 to 9v of CV without distortion.
rgds Pav

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Post by Synthbuilder » Mon Jul 01, 2019 3:55 pm

Pav wrote:I have -4.5v to -7v on pin 7 of U10 which from previous comments in the thread is not good. its jumping around a lot.
Yep, not good. If it's jumping around and its not just the voltmeter or scope probes not making proper contact then suspect a cold solder joint somewhere. But it is odd that you can calibrate F_OFF2 if this is happening.
Does the BP /Shape select switch have any impact on calibration?
or if shape selected LP or HP.?
No. The shape switch is after the filter circuit. But if it does you may have a problem on the pot board around that switch.
what am i getting when shape selected and pot is half way between LP & HP:hmm:
You should get a notch response. A sort of weak phaser effect.
If I back off the sub oscillator using the mixer - it goes away.
Can you hear it from the mixer's output or the sub's own output? If not I suspect the filter is misbehaving. I wouldn't expect the sub's behaviour to be affected by the level that is being sent from the mixer. It is possible to overdrive at certain filter settings with the main output if the trimmer A_LVL is set quite high.

If you can hear it from the sub out as well it may be that you need to swap out U21 with another 4093.

Tony

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Post by Pav » Tue Jul 02, 2019 1:24 pm

Thanks for the clues. Just starting to revisit the problem.

>> Can you hear it from the mixer's output or the sub's own output?
Yes but now the envelope is out of the equation and scope attached it becomes clearer.

From the sub out ..I get the triangle wave and as i traverse the notes up the keyboard. (where i previously heard noise like distortion from the main out_ , now appears to be the vco1 core (sawtooth) breaking in over the top of the sub osc.
It is a voltage thing as increasing the vco1/2 FM control modulation can recreate this.


So ill swap U21
EDIT -Solved That has done the trick. I had put a brand new CD4093BCN in originally and now have gone back to a new-old looking 4093BE. Not sure if spec made a difference. :bananaguitar:

I still need to fix the F_OFF1 issue. THe flickering has gone with a stronger ground connection of the dmm probe.
Minimum F_OFF1 pin 7 is -2.97 cannot get closer to 0.0.

U14 swapped - no difference.

its zebadee time - so time to stop.
rgds Pav

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Post by Synthbuilder » Wed Jul 03, 2019 2:31 am

Pav wrote:Solved That has done the trick. I had put a brand new CD4093BCN in originally and now have gone back to a new-old looking 4093BE. Not sure if spec made a difference.
Interesting. The square wave that drives the divide by two circuit that makes the sub is created with the 4093 Schmitt trigger from the sawtooth. The sawtooth is slightly processed by R70, R81 and D15. I was thinking about putting a trimmer in series with R81 just in case the 4093 wasn't behaving in a typical fashion. I did the calculations and I reckoned that there was only a very small possibility of some 4093 not working properly. So I bought a batch and tested each one and none of them displayed a problem. So I didn't bother with the trimmer.

I think the reason that it is more likely to go bad at high frequencies is because of the fixed high frequency compensation (R38) in the VCO. This reduces the output amplitude slightly at high frequencies which was just enough to push the 4093 out of my desired sweetspot and misbehave. I would think that reducing R81 to 91K may also do the trick in this instance.
Minimum F_OFF1 pin 7 is -2.97 cannot get closer to 0.0.
Not sure what's causing this though.

What's the voltage on pin 12 of the LM13700?

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Post by Pav » Wed Jul 03, 2019 11:11 am

todays readings are

pin12 U14 -0.22 V

pin7 U10 -2.2 V

the trimmer F_OFF1 is a Bourn 336 and fully clockwise.

The tiny variations im reporting in the next set of readings are temparature drift as board is under a lamp.


pin7 now -2.9

U14 pin readings

p1 -14 p16 -14
p2 -2.8 p15 -2.9
p3 0 p14 0
p4 0 p13 0
p5 +0.48 p12 -2.9
p6 -14.99 p11 +14.99
p7 0 p10 0
p8 0 p9 0


pin7 now -3.08

J201s

Q5 G +0.47 S -0.01 D +14.93
Q6 G -0.31 S -3.1 D +14.93
:hmm:


voltage across R77 shows -1.17V across R78 is 0.0
R71 shows -9.93 v across R72 is 0.0


R73 +2.64
R74 0
R76 -0.02


reflowed J201s ..no change.
rgds Pav

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