Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1340 on: August 06, 2018, 11:05:08 PM »
In the continuity setting on the meter with positive lead on the cathode and negative on the anode it goes from .5m and continues up.  the other way around it go 170k and continues up. 

in the diode setting with the positive lead on the anode I get .563 vdc and reversing the leads shows overload.

Diode test seems ok.  Did you say you have another kit?  Can you try that diode?
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1341 on: August 06, 2018, 11:39:58 PM »
Pulled and tested the other units CR8.

 .618 vdc with positive on the anode and overload with positive on the cathode with the diode setting.

.750 and up + on the cathode and 290. k and up + on the anode continuity test .

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1342 on: August 06, 2018, 11:41:23 PM »
Pulled and tested the other units CR8.

 .618 vdc with positive on the anode and overload with positive on the cathode with the diode setting.

.750 and up + on the cathode and 290. k and up + on the anode.

Does it work in the unit you're working on?
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1343 on: August 06, 2018, 11:53:55 PM »
swapped it in 19.72 vdc at the cathode test point and -9.66 at CR9 test point.

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1344 on: August 06, 2018, 11:58:40 PM »
swapped it in 19.72 vdc at the cathode test point and -9.66 at CR9 test point.

And it was fine before you stuffed the rest of the PCB?

You must have something dragging down your rail. 

-Look for shorts.
-Misplaced resistors.
-Backwards caps.
-Check your DCV transistor voltages against the trouble shooting doc.

Mike
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1345 on: August 07, 2018, 12:12:45 AM »
checked all the polarized caps and made sure they are oriented correctly.

In the process of double checking the resistors,

Is there a specific area to check around that would be dragging the voltage down? Wouldn't the low voltage effect all the reading on the transistors making them incorrect?

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1346 on: August 07, 2018, 12:50:56 AM »
checked all the polarized caps and made sure they are oriented correctly.

In the process of double checking the resistors,

Is there a specific area to check around that would be dragging the voltage down? Wouldn't the low voltage effect all the reading on the transistors making them incorrect?

True.

No need to check every single resistor carefully.
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1347 on: August 07, 2018, 09:56:27 PM »
checked every resistor off the list all correctly populated.

transistor voltages:

Q2:   G=1.7      S=4.4       D=5.5

Q3:   E=5.7     B=5.5        C=5.8

Q4:    G=1.2   S=2. 2 D=2.2

Q5:    E=8.22   B=8.32  C=8.4

Q6:   E=7.55    B=8.26    C=10.38

Q7:   E=3.41   B=3.98    C=12.0

Q8:   E=11.52    B=12.18  C=20.09

Q9:  E=2.5    B=3.1  C=19.66

Q10:  E=19.5    B=19.6   C=19.8

Q11:  G=-0.26    S=0.42   D=0

Q12:   E= -1.0  B= -0.4  C= -0.5

Q13:  E=-1.2   B=-0.6  C=-0.5

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1348 on: August 08, 2018, 02:40:56 PM »
checked every resistor off the list all correctly populated.

transistor voltages:

Q2:   G=1.7      S=4.4       D=5.5

Q3:   E=5.7     B=5.5        C=5.8

Q4:    G=1.2   S=2. 2 D=2.2

Q5:    E=8.22   B=8.32  C=8.4

Q6:   E=7.55    B=8.26    C=10.38

Q7:   E=3.41   B=3.98    C=12.0

Q8:   E=11.52    B=12.18  C=20.09

Q9:  E=2.5    B=3.1  C=19.66

Q10:  E=19.5    B=19.6   C=19.8

Q11:  G=-0.26    S=0.42   D=0

Q12:   E= -1.0  B= -0.4  C= -0.5

Q13:  E=-1.2   B=-0.6  C=-0.5

Try removing a few resistors to see if your +30 VDC rail comes back to normal.  You can just lift one of the legs off the PCB. After you lift a leg on each part...test to see if the rail is back.  Unplug the unit while removing. 

This is a Rev A correct?

-R17
-R51
-R35

Any of those get it back to +30 VDC?

Mike
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1349 on: August 08, 2018, 05:16:56 PM »
Yeah its rev A, I'll give that a shot.


Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1350 on: August 08, 2018, 05:38:25 PM »
did them one by one R35 last and that one or all together brought it back to 30 at the cathode. checked resistance on each of them:

R51=4.26K

R35=8.20K

R17=4.594K

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1351 on: August 08, 2018, 05:58:07 PM »
did them one by one R35 last and that one or all together brought it back to 30 at the cathode. checked resistance on each of them:

R51=4.26K

R35=8.20K

R17=4.594K

Look at the schematic:
https://www.hairballaudio.com/uploads/pdf/fet_rack_a_v1.14_voltages.pdf

Something after R35 is wrong or dead.  Put R35 back in(confirm it drops again) and try removing Q4 then Q5. See if it bounces back to 30. If so one of those it dead, or a resistor is wrong around it.

Also check CR1 with a diode tester (roved from PCB) and check caps in that section.

Mike
Hairball Audio, LLC
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1352 on: August 08, 2018, 09:15:28 PM »
resoldered R35 back to 20vdc

removed Q4 no change. Removed Q5 back to 30.86vdc.

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1353 on: August 08, 2018, 09:17:33 PM »
resoldered R35 back to 20vdc

removed Q4 no change. Removed Q5 back to 30.86vdc.

Google how to test a transistor with a diode tester. Test it.
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1354 on: August 09, 2018, 02:23:16 PM »
Q5 checks out with a diode tester vdc drops to .67 at the right spots.

 I tried to plug it into a sh*ttier meter's hFE tester but it wasn't giving me any reading. I got to find my junk box and test some other trannys to see if the meter is working right.

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1355 on: August 09, 2018, 02:36:27 PM »
Q5 checks out with a diode tester vdc drops to .67 at the right spots.

 I tried to plug it into a sh*ttier meter's hFE tester but it wasn't giving me any reading. I got to find my junk box and test some other trannys to see if the meter is working right.

I'm going to be offline for a few days.  If you email me your address today, I can drop a replacement in the mail for you before I'm gone.  info at hairballaudio dot com.

Triple check everything around that transistor...something is shorted or wrong.  Getting close!

Mike
Hairball Audio, LLC
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1356 on: August 09, 2018, 05:12:47 PM »
Thanks Mike I'll shoot you an email.

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1357 on: August 14, 2018, 06:00:10 PM »
Got the package, thanks again.  There wasn't any cn4/cn5 connectors, removed the off button by force off the old board to get at the solder joints to salvage the old connectors but the plastic bit didnt stay connected to the pins after heating everything up. Bummer.

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1358 on: August 14, 2018, 06:09:45 PM »
Got the package, thanks again.  There wasn't any cn4/cn5 connectors, removed the off button by force off the old board to get at the solder joints to salvage the old connectors but the plastic bit didnt stay connected to the pins after heating everything up. Bummer.

Never remove anything by force, it will break and or damage the PCB. Always use a proper desoldering tool.  We'll send you a CN4/5 today.
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1359 on: August 14, 2018, 06:51:55 PM »
both connectors cn4 and cn5 are junk after heating  them enough to get all the leads free, hot pins just warp the plastic. 

By force I mean I snipped the leads I could access and removed solder where I could with wick to get it free to access the pads for the connectors.

CR1 tested fine but I might as well replace it with the one you sent.

Not sure where to go from here.  It would be a waste of time to stick the replacement trannys in if the problem is somewhere else. I guess recheck everything in the line amp section