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

[emrr]

I recall measuring the sh*t out of every R as it went in there, especially R6-8 which with tolerances, can look like one another.  Build pic looks like the R string is correct, unless I'm missing something.  What do you see?

https://c4.staticflickr.com/8/7715/17610318049_0f74d64e0a_o.jpg

 

[jsteiger]

Yes from what I see those are correct. With the way the string is set up, only the green LED should fire with 2.487V present on TP10. That is interesting and at the moment, puzzling. I think the data I am collecting for the DCV's at the LM339 pins may help narrow down the issue.

 

[radrobgray]

I built my first FC526 no issue. Just completed the second one and it will not power up. It is causing my Radial Workhorse Powerstrip to go into protect mode. I double checked diode/capacitor orientation/values and resistor values. I'm stumped. Here are a few pictures of the board.

 

[jsteiger]

I built my first FC526 no issue. Just completed the second one and it will not power up. It is causing my Radial Workhorse Powerstrip to go into protect mode. I double checked diode/capacitor orientation/values and resistor values. I'm stumped. Here are a few pictures of the board.

The TL084 is in backwards.

 

[radrobgray]

I built my first FC526 no issue. Just completed the second one and it will not power up. It is causing my Radial Workhorse Powerstrip to go into protect mode. I double checked diode/capacitor orientation/values and resistor values. I'm stumped. Here are a few pictures of the board.

The TL084 is in backwards.

Doh! Thanks,  I got it on correctly and it powered up. I'm trying to calibrate the metre now and I can only get 1.76v at TP10. Did I fry the TL084?

 

[jsteiger]

Most likely, yes.

 

[radrobgray]

Any reason I couldn't sub a TL074 in this application? That's what I have on hand. If not I'll have to bite the bullet and order parts. I really appreciate the help and quick response.

Thank you!

 

[jsteiger]

Any reason I couldn't sub a TL074 in this application? That's what I have on hand.

It should be fine.

 

[radrobgray]

Replaced the TL084. It's still won't trim up past 1.76v on TP10. what else should I be checking?

 

[jsteiger]

Replaced the TL084. It's still won't trim up past 1.76v on TP10. what else should I be checking?

What is your voltage at TP9? Should be -10V.

 

[radrobgray]

TP9 is giving me -8.56

 

[jsteiger]

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.

 

[emrr]

Can you check for 2.5V DC at the precision shunt on the meter card?

2.58VDC at the center pin of one, 2.6VDC on the other.

 

[tctonn]

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.

Hi Jeff,

I am putting together a pair of these now. Would you recommend making this swap at R41 on kits that I bought in your last batch of 50?

Also, should I be concerned that in my kits the 300k (R39, R40) and 1M (R37, R38) resistors are 5% rather than the 1% that is shown on the Rev A.2 PCB BOM?

Thanks as always for all your help with these.

 

[jsteiger]

Would you recommend making this swap at R41 on kits that I bought in your last batch of 50?

Absolutely yes, This will only make your life easier and the reference voltages will be solid if you slip in it another rack somewhere.

Also, should I be concerned that in my kits the 300k (R39, R40) and 1M (R37, R38) resistors are 5% rather than the 1% that is shown on the Rev A.2 PCB BOM?

No not at all. The parts are actually correct. I just need to update the BOM. The clerical part slipped thru the cracks on those  :-[

 

[emrr]

Paralleled an actual 2161R across the 1K2 to get about 771R at R41, no time to go further....

 

[jsteiger]

Can you check for 2.5V DC at the precision shunt on the meter card?

2.58VDC at the center pin of one, 2.6VDC on the other......

This is a problem Doug. This should be between 2.497V and 2.503V. I have recently tested and verified that this voltage will be rock solid with a supply voltage ranging from 14.5V to 20V at the gold fingers. I would look at R14 on the meter PCB and make sure its 5k1.

 

[jsteiger]

Paralleled an actual 2161R across the 1K2 to get about 771R at R41, no time to go further....

This will also work a treat. I would call that being a tricky *******!

 

[emrr]

2.58VDC at the center pin of one, 2.6VDC on the other......

This is a problem Doug. This should be between 2.497V and 2.503V. I have recently tested and verified that this voltage will be rock solid with a supply voltage ranging from 14.5V to 20V at the gold fingers. I would look at R14 on the meter PCB and make sure its 5k1.

OK, ASAP.

Paralleled an actual 2161R across the 1K2 to get about 771R at R41, no time to go further....

This will also work a treat. I would call that being a tricky *******!

I call it 'F pulling the boards out, take the shortest path'. 

 

[jsteiger]

OK I apologize for this not being a better quality. I will put something more professional together when I have a minute. I am heading down to Nashville early tomorrow morning and have not packed anything yet!

In the attachment, you will see a chart of points to check the comparator string. The numbers are merely the junction of the resistor string, not component pin numbers. It starts with the 2.5V precision shunt so if that is off, the whole string will be wonky.