[BUILD] CAPI FC526~500 Series~FET Limiter Kit~Official Support Thread

[jsteiger]

BTW, by changing R41 to 750R, I have verified on multiple units here that the -10V rail stays rock solid from a supply voltage ranging from -14.5V to -20V. That is a supply voltage at the gold fingers coming to the card. The 2.5V rail is rock solid as well from the same voltage range.

 

[dandeurloo]

BTW, by changing R41 to 750R, I have verified on multiple units here that the -10V rail stays rock solid from a supply voltage ranging from -14.5V to -20V. That is a supply voltage at the gold fingers coming to the card. The 2.5V rail is rock solid as well from the same voltage range.

Jeff, will I need to re calibrate if I make this change to mine?

 

[orenradio]

I imagine this resistor is the recommended replacement for R41?  I haven't had the chance to start my pair of compressors just yet, might as well get the right resistor in there before I start.  Jeff I know you are out of town, so no rush... just want to be sure

http://www.mouser.com/ProductDetail/Xicon/271-750-RC/?qs=sGAEpiMZZMu61qfTUdNhG6G26YXWwWp0cxSUK4uuyRQ%3d

 

[radrobgray]

TP9 is giving me -8.56.

OK that is your issue for TP10. I am changing the kits and including a 750R for R41 on the main PCB. Right now its a 1k2. Swap that out if you have something close and then make sure you have -10V at TP9. That is a crucial measurement to take. If its not -10V, the Q-Bias and meter cal will never happen correctly.

Did the swap on R41 to a 750r TP9 is now 10.02v but I can only get TP10 to 2.06v. Only the bottom led on the meter will "trim off" at that voltage.

 

[jsteiger]

Dan, you should not have to recal after making that change. Just verify that your -10V rail does not change. This just means that the -10V rail will be stable no matter what rack or power supply voltage you use.

Yes orenradio that is the right part. I can mail them to you when I get home on the 31st.

radrobgray, I would start by adjusting the front panel trimmer and the 100K trimmer to their mid position at 50% rotation. Just turn them until you hear them clicking when they reach the end, and then turn the opposite way approximately 12 rotations. That should be near the center. If the 100K trimmer gets turned to far it will seem like you cannot adjust the front panel trimmer to bring the voltage up properly. Hope that makes sense.

 

[bacbacou]

hello Jeff,

I have +/-15V power supply, so I am going to put R41 750r,
but do I have to change another resistor to stabilize the 2,5V rail ?

regards,

Richard

 

[radrobgray]

radrobgray, I would start by adjusting the front panel trimmer and the 100K trimmer to their mid position at 50% rotation. Just turn them until you hear them clicking when they reach the end, and then turn the opposite way approximately 12 rotations. That should be near the center. If the 100K trimmer gets turned to far it will seem like you cannot adjust the front panel trimmer to bring the voltage up properly. Hope that makes sense.

Tried that to no avail. Any other things I should check. Still only trims to 2.07v.

 

[jsteiger]

hello Jeff,

I have +/-15V power supply, so I am going to put R41 750r,
but do I have to change another resistor to stabilize the 2,5V rail ?

regards,

Richard

Nope just R41

 

[jsteiger]

radrobgray, I would start by adjusting the front panel trimmer and the 100K trimmer to their mid position at 50% rotation. Just turn them until you hear them clicking when they reach the end, and then turn the opposite way approximately 12 rotations. That should be near the center. If the 100K trimmer gets turned to far it will seem like you cannot adjust the front panel trimmer to bring the voltage up properly. Hope that makes sense.

Tried that to no avail. Any other things I should check. Still only trims to 2.07v.

I'm out of town at the moment so can't help much until I return.

 

[emrr]

strapped R41 (1K2) with 2161R (771R resulting).
checked R14 is 5K1, both look correct, without outright pulling them.  Color code right, read reasonably right in circuit.
checked CR1/Q1 placement, both units correct.
PSU back to +/-16.04V, +/-16.01 at connector.

#1
TP9 -9.98V
2.595V at CR1: F#CKED
tried meter cal, still 3 yellow lit with +2.487 at TP10

#2
TP9 -9.98V
2.573V at CR1: F#CKED
tried meter cal, still 2 yellow lit with +2.487 at TP10

Now officially more time in troubleshooting than building.....

bad CR1's?  What else? 

 

[jsteiger]

What are you using for the ground reference Doug? The green zero LED is suppose to trip just below the ref voltage at CR1 or at point #1 in my above pic of the meter PCB.

 

[emrr]

GND at top of board as specified.

 

[jsteiger]

Ok. Does the ref voltage (high as it is) fluctuate if you raise or lower the positive supply voltage? I am still not back to the lab but in my previous tests, mine was solid. I tried to make it go above 2.5 but could not duplicate your situation. I would not go less than 14 V or higher than 20 V when checking it.

 

[emrr]

I'd assume that's a test done with op amps out? 

I did note one was easy to trim to +2.487, the other jumps around quite a bit during adjustment and is lucky to land at +2.486 or +2.488.

I'm wondering if this is a rack problem, grasping at straws.  The test bed is an OSA rack, 8 other types of modules work fine in it.  I have the 10R at the connector for front/back ground.  I should try it in a different rack, which is a bit of a PITA to arrange. 
http://groupdiy.com/index.php?topic=48324.0
This may be it.
--EDIT: IT IS!---
As well, my extension jig has no pin 1 connection, so that's a 'double no pin 1'.

 

[jsteiger]

I did it with opamps in. I would adjust the negative rail by a volt or 1.5 and then the pos by a volt or 1.5, stepping my way up to 20 and down to 14. I have so far had my hands on nearly 30 of these completed modules and never had one with the meter reference voltage higher than 2.5. Once calibrated on my bench supply, they have ended up in various different API racks as well as BAE and the green zero LED illuminates right away with no trimming required.

 

[jsteiger]

Doug, can you check the attachment I posted on page 4 of this thread. Post #79. I know your reference voltage will start out a bit high, but see if the rest of yours follows a similar pattern to mine. This is the reference voltage down the resistor string that the comparators look at.

 

[emrr]

I never mention the green LED, but it does light, along with the specified # of yellow.

Spoiler:
Both units, moved to 51X rack, only green LED lit.  F!  OSA rack!!!!

backtracking:

Is this a (lack of) pin 1 problem with OSA rack?
FC526 top and bottom ground planes link through 10R between pin5 and pin13.
FC526 pin1 - 10R - pin13 - 10R - pin5
FC526 GND lug is pin13, shorted.

Connecting OSA pin1 to PSU chassis changes nothing.
If I short pin5/13 while in OSA rack, yellow LED’s go out leaving only green on both units, and green turns off in ABI on both.


Pin5/13 not shorted in these measurements, 2.486V TP10.
is: should be:
IC2-5 2.362 eight) 2.276 (Eight does this 8) dangit stupid sh#t 8))
IC2-7 2.339 9) 2.253
IC2-9 2.264 10) 2.178
IC2-11 1.771 11) 1.685

IC3-5 2.466 4) 2.38
IC3-7 2.437 5) 2.351
IC3-9 2.412 6) 2.326
IC3-11 2.386 7) 2.3

IC4-7 2.584 1) 2.498
IC4-9 2.536 2) 2.45
IC4-11 2.504 3) 2.417

Other w/2.487V TP10:
is: should be:
IC2-5 2.359 8) 2.276
IC2-7 2.336 9) 2.253
IC2-9 2.262 10) 2.178
IC2-11 1.773 11) 1.685

IC3-5 2.462 4) 2.38
IC3-7 2.434 5) 2.351
IC3-9 2.408 6) 2.326
IC3-11 2.383 7) 2.3

IC4-7 2.597 1) 2.498
IC4-9 2.55 2) 2.45
IC4-11 2.518 3) 2.417

ready to align in 51X rack!!  Rewire damn OSA rack!!

Note the 51X rack and the OSA rack are on the same power supply. A module on the extension jig in the 51X rack  shows only the green LED with that extension jig lacking pin1 chassis connection .

No chance yet to check CR1 or LM339 voltages again in 51X rack.  Since the lack of pin1 on the test jig makes no difference here, I'm not sure yet what's actually different.  Pin5/13 shorted in the 51X rack?

 

[jsteiger]

.....and green turns off in ABI on both.

This is totally normal and to be expected. Switching to All Buttons In takes the FET fully out of the conductive range so the green LED will turn off. The same thing happens with a real 1176. If the meter is in GR mode, when pushing ABI (or just 4 and 20), the meter will increase (positive voltage) by the amount of the FET cal which will typically be 1dB in a later model real one, providing that the meter and FET are all cal'ed in correctly!

As for the rest, it is now making sense that the 10R between the ground planes is offsetting the 2.5V reference since the OSA rack must not have a link between pins 5 and 13 internally.

I was curious before about how consistent your reference voltage was at the top of the string (IC-4 pin 7) when running your PSU voltage up and down. Even though it is offset above 2.5V, it should stay consistent and never change. Would be swell if you could verify this 

Option #1, I would cal the units in the 51x rack so the voltages you are looking for are easy to hit and already known. Once you move them to the OSA rack, just simply re-zero the green LED. Do this thru the front panel while racked up. I would not measure the voltage. Just make sure the green LED just barley comes full on. The meter cal should stay set from before as everything will shift together.

Option #2, remove the 10R that links the top and bottom ground planes and replace with a jumper wire or zero ohm R.

 

[djroshi]

Checking in.

R41 is now a 750R and I have a solid -10 at TP9.

Still unable to calibrate the meter.

1. With GR off and +2.487V at TP10 green led is lit.
2. Engage GR and green led is now OFF. I have 7db GR verified and TP10 is greater than +2.245V so I turn RV8 CCW till I reach the desired voltage - green led is still OFF.
3. I disengage GR and TP10 is now less than +2.487V so I turn RV1 CW to get the desired voltage.
4. Repeat 2 and 3. The voltages seem to get further and further apart needing greater adjustments.

I have gone thru and compared the voltages at the comparator ICs and they seem to align closely to the measurements you posted Jeff (thanks for that BTW).

 

[emrr]

Yup on the ABI action, just confirming it's acting right which also shows that alignment step 1 is correct, if I'm not mistaken. 

It is not simple to change the PSU voltage here.  I'll try to wind it down a bit and see.  It goes up no further than +/-16.37V.

I haven't taken the time to dig further into proper VPR wiring standard, so 5 and 13 are typically shorted in the racks?  I'm sure you have a chart somewhere....

Good to know the details of option 1. 

I think I will try option 3: rewire the damn OSA rack properly.  I mean really; XLR output shells as only thing wired to chassis?  How often is that likely to work (sarcasm intended)?