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The Kuartlotron - keantoken's simple error-correction superbuffer
The Kuartlotron - keantoken's simple error-correction superbuffer
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Old 3rd February 2017, 03:45 PM   #791
Fitero is offline Fitero  Canada
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I received my boards and components in lightning speed and began to throw them together yesterday.
I yanked out my tube preamp from it's chassis and screwed in the boards and began to trim them.

In my haste and ignorance I didn't think to provide a ground to the boards. Of course I couldn't get anywhere with them. I stared at the buffer boards for awhile trying to figure out where I had screwed up too. It didn't occur to me until quite a bit later what I had done wrong. Like I said; ignorance.

This weekend I'll ground them to something and give it another shot.
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Old 4th February 2017, 05:13 PM   #792
Fitero is offline Fitero  Canada
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OK, I'm stumped.

I used 68R resistors on the * marked locations as I have a 12VDC, LPS that I want to use for this. In order to get +/- 10VDC at the test points on the board I have to lower the input voltage from the LPS to 11.5VDC.

I'm using a SOLA / HEVI-DUTY SLS-12-068T power supply.

Using R5, I can get 5VDC at the test point with input shorted.

Removing the short from the input and adjusting the DC trim pot I can zero out the voltage on the input.

However, after all of this I still measure between .068VDC to .073VDC on the output. Both boards are like this.

I couldn't figure out the board grounding requirements, and initially powered the board up without one. Today I connected a ground lead from the board to the LPS chassis ground and then to AC ground. Nothing changed.

I was grounded while handling and soldering the transistors.

Any ideas on what I have done wrong????
Thank you

Last edited by Fitero; 4th February 2017 at 05:16 PM.
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Old 4th February 2017, 08:16 PM   #793
BRN is offline BRN  United States
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I looked up the power supply your using and it looks like it only provide positive 12 VDC. The boards need positive and negative DC to power them.
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Old 4th February 2017, 09:59 PM   #794
Fitero is offline Fitero  Canada
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Haha!!! Whatta dope I am!

Thank you for pointing out what should have been glaringly obvious BRN!!!
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Old 5th February 2017, 02:43 AM   #795
keantoken is offline keantoken  United States
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Thanks for spotting that BRN!
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Old 22nd February 2017, 09:16 PM   #796
lacro is offline lacro  United States
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Got my boards put together. I followed the trimming procedure, which worked ok on one board, but not the other.

The power supply is 12v, and the on-board regulator resistors are 68R

I can't get the DC trim pot to zero volts on the input. It stays at 1.4V regardless of the trimmer setting.

One of the TL 431 regulators gets pretty hot quickly when power is applied.

I installed the second board in a mono system, and it seems to be working fine, and does not get hot.

Any suggestions where to start looking?

Thanks,
Lacro
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Old 23rd February 2017, 01:47 AM   #797
keantoken is offline keantoken  United States
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I would list the voltages at each transistor and TL431 pin. Is it possible your power supply is the wrong configuration? The board needs +-12V with 0V being ground.
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Old 24th February 2017, 03:45 PM   #798
lacro is offline lacro  United States
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Quote:
Originally Posted by keantoken View Post
I would list the voltages at each transistor and TL431 pin. Is it possible your power supply is the wrong configuration? The board needs +-12V with 0V being ground.
Thanks for the suggestions. The power supply is the correct configuration (+-12V with 0V being ground) I checked the voltages at the TL431's. On the good board the regs are both 10V, on the bad board one is 10V, and the other is 6.6V

Which pins should I use to check voltage at the transistors (E,B,C)

The only thing I think that may be possible I did wrong was swapping the leads from the PS, V- with grd. during the first connection to the PS. I don't think I did that, but it's possible or maybe a static discharge from me, as I don't have myself grounded continuously, just touch a ground every 10 minutes or so. Any more suggestions appreciated.

Thanks,
lacro
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Old 25th February 2017, 05:38 AM   #799
keantoken is offline keantoken  United States
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Put one probe on ground and then just touch each pin with the other probe. Either the TL431 is dead, or something is shorting across it and lowering the voltage.The lytics would probably protect the Kuartlotron from swapped power, but I don't know how the TL431 reacts.
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Old 27th February 2017, 03:45 PM   #800
lacro is offline lacro  United States
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Ok, I swapped both TL431 regs, and the 68R resistor that gets hot from the good board to bad board. No change, but the regs/resistor from the bad board work fine on the good board, so It looks like the TL431's are ok, but one reg still gets hot as does the resistor even though they have been replaced.

I checked multiple times with a jewelers eye loupe for any possible shorts, top and bottom, but nothing.

The voltages at the transistors are all over the place, and are different than the good board.

The voltages for the BC560:

The one closest to the 1k resistor:
1(collector)= negative .21v
2(Base)=0.16v
3 (Emitter)= 0.75v

The one closest to 56R resistor:
1=.75v
2=8.5v
3=9v

The voltages for the BC550:

The one closest to the 1k resistor:
1=8.5v
2=0.75v
3=0.16v

The one closest to 56R resistor:
1=10v
2=9v
3=8v

When I check the voltage at the open unused +10v, and -10v holes, I get 10v on the +10v hole, and 4v on the -10v hole.
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