Cornet 2 LED reversed

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Philip A

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Cornet 2 LED reversed
« on: 4 Oct 2014, 06:01 am »
Hello all.

My name is Philip.  I have just finished two (2) Cornet II's.  One for my brother in-law and one for me.  The problem I am having is that both power up, but there is no sound.  Let me first say that both units are identical, and I have sub in a known good phono stage in my system and it works.  Let me also say that I have double checked the wiring and soldering and they both seem good.  The LED for both units starts off GREEN and then turns RED after about 15 seconds.  My understanding is that this is backward to the way the LED should work.  The Sovtec 5Y3GT glows, but the other tubes do not.  I have not checked any of the voltages as yet.  It is 1:55am here!  I hope that someone can put me on the right track.  Thank you in advance.

poty

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Re: Cornet 2 LED reversed
« Reply #1 on: 4 Oct 2014, 07:13 pm »
First of all you should check the voltages for tubes' heating. Transformer wires to the PCB, diodes' polarity, the polarity of the electrolytic capacitors in the heating circuit...

Philip A

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Re: Cornet 2 LED reversed
« Reply #2 on: 4 Oct 2014, 09:16 pm »
Hello Poty.  Thank you for the reply.  I will check those tonight.  After sleeping on the problem last night I also think the issue lies on the transformer side.  I will let you know what I find.  Thank you again!

hagtech

Re: Cornet 2 LED reversed
« Reply #3 on: 5 Oct 2014, 04:08 am »
For one, the LED is backwards.  Better check other polarized parts (like the diodes poty mentions).  Check heater voltage.

jh

Philip A

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Re: Cornet 2 LED reversed
« Reply #4 on: 5 Oct 2014, 04:30 am »
Hello jh.  Thank you for the reply.  Can't believe I soldered in both LED backwards!  What are the chances?  This is the first full on build that I have done.  I will check the diodes and voltages tonight.  Thank you again!  Will follow up soon. 

Philip A

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Re: Cornet 2 LED reversed
« Reply #5 on: 5 Oct 2014, 07:01 am »
Hello all.  First let me apologise for my lack of electronics knowledge.  I have checked the diode and electrolytic placement and the seem correct.  My voltages however are way out.  I am measusing DCV from ground the the PCB.  The values are;

R107-456VDC                                         
R219R-5VDC and dropping to 1VDC            R219L-5VDC and dropping to 1VDC
R212R-430VDC                                         R212L-430VDC
R204R-430VDC                                         R204L-430VDC
R211R- 452 and 438                                 R211L-451 and 438

I hope someone can help.  Thank you again.

hagtech

Re: Cornet 2 LED reversed
« Reply #6 on: 5 Oct 2014, 10:11 pm »
Looks like you don't have heaters.  Or are you measuring without tubes?

jh

Philip A

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Re: Cornet 2 LED reversed
« Reply #7 on: 5 Oct 2014, 10:30 pm »
Hello jh.  Those measurements are with the tubes installed.  All tubes are brand new.  Just purchased the Sovtec 5Y3GT tubes from Parts Connextion in Toronto Canada.  I have not checked the voltages on the other C2 at this time.  Both units have their own tubes, and the are both not functioning.  Only the rectifier tubes glow.  Thank you again for your continued help.

Philip A

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Re: Cornet 2 LED reversed
« Reply #8 on: 7 Oct 2014, 07:52 am »
Hello Jim and Poty.  I have been searching around on the site to try and find an answer to my problem, but no luck so far.  I was wondering if you had any thoughts on where I have gone wrong.  Would some pictures of both C2's help?  Thank you again.

poty

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Re: Cornet 2 LED reversed
« Reply #9 on: 7 Oct 2014, 09:00 am »
Something wrong with your heaters circuit. Could you measure the following points:
1. AC voltage across С102 (or R103).
2. DC voltage across С106 (check the polarity also!).

Philip A

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Re: Cornet 2 LED reversed
« Reply #10 on: 7 Oct 2014, 02:34 pm »
Hello Poty.  I have checked both units.  I have confirmed that all caps are polarity correct. Diodes are also in correct. Voltages are;


                                                  Unit 1                      Unit 2
AC Voltage across R103                7.64VAC                  7.56VAC
DC Voltage across C106               10.01VDC                9.78VDC

Thank you again for the help!

poty

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Re: Cornet 2 LED reversed
« Reply #11 on: 8 Oct 2014, 06:20 am »
Seems OK for me. It explains that LEDs are working as intended, but it does not explain the lack of heating in your amplifier tubes. So, I'd like to know (all DC voltages) across C209 (or C210, or C211), across R223.
Make the abovementioned measurements twice please: with and without tubes (I mean V200-V202, not the rectifier).
Could you also post a photo of insides?

hagtech

Re: Cornet 2 LED reversed
« Reply #12 on: 8 Oct 2014, 07:51 am »
I'm going to take a long shot here and guess you installed 1.5k or 1.8k for R223...

jh

Philip A

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Re: Cornet 2 LED reversed
« Reply #13 on: 8 Oct 2014, 01:03 pm »
Hello Poty and Jim.  Thank you for the reply...again!  Jim you are amazing.  You are absolutely correct.  I ordered and installed a 1.8k resistor in R223.  ordering the correct resistor now.  Thank you again.  Will update soon with pictures.  Thank you both for all your support!  Have a great day.

Philip

Philip A

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Re: Cornet 2 LED reversed
« Reply #14 on: 10 Oct 2014, 05:02 am »
Hi Jim an Poty.

Success!  Jim, you are a genius.  Swapped out the 1.8K resistor for the 1R8 that I should have installed :duh:  Both units sound great!  The resistance measured 1.5 ohms and 1.6 ohms.  Do you think this is a bit low?  I also have a bit of hum on one unit.  Not sure if it is there in the other.  I will try swapping tubes tomorrow to see if that makes a difference.  Pictures will follow Saturday.  Thank you again Poty and Jim.  Great product Jim.  I am looking forward to the next build.     

Philip A

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Re: Cornet 2 LED reversed
« Reply #15 on: 13 Oct 2014, 04:58 pm »
Hello all.

Sorry for the delay.  I have been busy tweeking the Cornet2 over the last few days.  Twisting wires, checking grounds.....  I did find that I had to lift the ground on the power cable that feeds the C2 to try and reduce hum.  This had some effect at reducing things, although I know this is not the best fix.  I will be adding some shielding and different wires for the inputs and outputs.  As promised here are the pictures of my C2.  Thank you Jim and Poty for all the help getting my C2 sorted! 








poty

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Re: Cornet 2 LED reversed
« Reply #16 on: 16 Oct 2014, 06:38 am »
I'd not risk the safety disconnecting the safety ground from the chassis. Reducing hum in this case means some ground loops somewhere, probably in the next device in the chain too.
Marvelous look!  :thumb:

Philip A

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Re: Cornet 2 LED reversed
« Reply #17 on: 16 Oct 2014, 01:09 pm »
Hello poty.
Thank you again for your comments.  I will be reinstalling the ground on the C2, and replacing and shielding some of the wiring.  I am sure that this will resolve the hum problem.  Thanks again!  I would love to see pictures of other C2's if anyone would like to post them here.