Cornet 3 build issue

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kevrose

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Cornet 3 build issue
« on: 8 Sep 2014, 05:48 pm »
Hi,

Received my Kickstarter Cornet 3 kit today (I'm in the UK). I presume my Piccolo 2 will be along shortly...

When I switch it on, the LED lights up but the other two don't light up after 20 seconds (or much longer). I can't test it audiowise until I get the P2 but this seems like a problem?

Kevin

hagtech

Re: Cornet 3 build issue
« Reply #1 on: 9 Sep 2014, 05:45 am »
That's the power up delay for the high voltage.  With tubes you need to give the heaters some time to warm up and get the cathodes emitting electrons.

jh

kevrose

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Re: Cornet 3 build issue
« Reply #2 on: 13 Sep 2014, 08:24 am »
So, I've established the high voltage section is not working. Does anyone have any suggestions as to where I should start checking voltages etc to try and find out the root cause? Could the IC be at fault?

poty

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Re: Cornet 3 build issue
« Reply #3 on: 13 Sep 2014, 11:37 am »
It depends... How did you come to the decision?

kevrose

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Re: Cornet 3 build issue
« Reply #4 on: 13 Sep 2014, 12:32 pm »
Jim told me where to check to see whether the high voltage was kicking in.

poty

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Re: Cornet 3 build issue
« Reply #5 on: 13 Sep 2014, 06:45 pm »
I took a look at the schematic just an hour ago (did not know it was published), so maybe my suggestions will not be so effective.
As far as I understood the LED near the front panel lights up, it means (at least) that the basic voltage from the external PS is here.
I guess that you have checked the voltage across C5R26? It's better to check if the U1 is oscillating, but I can't see the way to do it without o'scope (if my countings are right the oscillating frequency is above the hearing capabilities - 48kHz). Then let's begin with visual checking: check if the U1, Q1, D1 have been soldered correctly (orientation and cold joints). Then check the D1 and the voltages on the Q1 leads. If you have a spare IRF740 you can try to change it.

kevrose

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Re: Cornet 3 build issue
« Reply #6 on: 14 Sep 2014, 10:44 am »
Thanks Poty, will do. I've checked all the resistors with a meter and they're correct. Have ordered a replacement tranny and IC and some different (better) solder (not that I've generally had a problem with the kits I've built in the past).

If the IC wasn't seated properly/installed would that damage any other components?

kevrose

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Re: Cornet 3 build issue
« Reply #7 on: 14 Sep 2014, 11:36 am »
If D1 is the diode physically next to Q1 then I'm getting 4v.

On the IC I'm getting the following:

1: 0v
2: 3v
3: 4v
4: 5v
5: 5v
6: 3v
7: 3v
8: 8v

Does this look right?

poty

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Re: Cornet 3 build issue
« Reply #8 on: 14 Sep 2014, 04:10 pm »
Have ordered a replacement tranny
Tranny?  :o Does the Cornet 3 have tranny?
If the IC wasn't seated properly/installed would that damage any other components?
I doubt it.
If D1 is the diode physically next to Q1 then I'm getting 4v.
on which end?
On the IC I'm getting the following:

1: 0v
2: 3v
3: 4v
4: 5v
5: 5v
6: 3v
7: 3v
8: 8v

Does this look right?
pin 8 and 1 - OK
pin 4 - unsure, in my opinion should be much lower.
pin 5 is unconnected in schematic
pin 2, 3, 6, 7 - have AC signal and then not so easy to deduce.

hagtech

Re: Cornet 3 build issue
« Reply #9 on: 18 Sep 2014, 03:49 am »
Can you post a photo?

jh

kevrose

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Re: Cornet 3 build issue
« Reply #10 on: 13 Oct 2014, 03:54 pm »
I took the Cornet 3 to a tube specialist here in London. He confirmed that the amp works when it was running from an external 210V power supply. However, the Cornet 3's power supply is only producing about 10V.

We've replaced the Mosfet and the transistor but still nothing, so he was wondering if the inductor(s) could be at fault?

Any one have any thoughts? Are they pretty standard i.e. should I be able to get them here in the UK? If so, what are their make/model?

If it's unlikely to be the inductor(s) and it's not the mosfet or transistor, is there much else it can be? (He was going to look into the chip timings or something as well, AFAIR).

hagtech

Re: Cornet 3 build issue
« Reply #11 on: 16 Oct 2014, 05:56 am »
Could be bad soldering.  That's been the trend lately...

jh

poty

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Re: Cornet 3 build issue
« Reply #12 on: 16 Oct 2014, 06:31 am »
We've replaced the Mosfet and the transistor but still nothing, so he was wondering if the inductor(s) could be at fault?
Any one have any thoughts? Are they pretty standard i.e. should I be able to get them here in the UK? If so, what are their make/model?
First of all even cheap DVMs nowadays are capable of measuring/testing an inductor, so it is better to test first before ordering the new one. The part number should be mentioned in your manual for Cornet 3 (if you've lost yours - there is an electronic version online on www.haglabs.com).
If it's unlikely to be the inductor(s) and it's not the mosfet or transistor, is there much else it can be? (He was going to look into the chip timings or something as well, AFAIR).
If your specialist has an oscilloscope it is better to check if the LM555 is producing an oscillations to the gate of the MOSFET.

kevrose

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Re: Cornet 3 build issue
« Reply #13 on: 20 Nov 2014, 04:26 pm »
So, it turns out the problem was a cold solder joint on one of the capacitors.

The Cornet 2 and Piccolo 3 sound great - my only issue now is that one channel is slightly louder than the other. I don't know how I can test whether it's the Cornet or Piccolo as I'm using a MC cartridge and don't have another phono stage...

Any ideas?

poty

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Re: Cornet 3 build issue
« Reply #14 on: 20 Nov 2014, 06:39 pm »
You can connect Piccolo directly to your preamplifier with smallest gain and use an smartphone, MP3 player or something like that. Dial minimal volume and listen to the difference between channels.
You can also buy our build an iRIAA and use any source with linear output instead of turntable.