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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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2nd Oct 2018, 5:30 pm | #1 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
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What does a blanking signal look like?
I am still trying to fix a Gould 4074. The power supply is now behaving itself and the 'scope appears to do what I might expect it to do - except there's no on-screen display.
There was a display when I first got some life from the power supply but that disappeared with the cracking sound of a component failing a few weeks ago. Using the service manual, there's a handy step-by-step guide to repairing the instrument which has been very helpful so far. Currently I'm working through Section 5/9 "No CRT Display" and have proved everything so far up to the instruction in 9.1 "Is the blanking signal present at the emitter of Q801" There is a signal, it's a sinusoidal shape about 200mV p-p but I don't know if that's a blanking signal or just noise. It looks like noise to me. Can anyone help to point me in a forwards direction again? Thanks,
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Richard Index: recursive loop: see recursive loop |
2nd Oct 2018, 5:56 pm | #2 |
Nonode
Join Date: Mar 2010
Location: Sunderland, Tyne and Wear, UK.
Posts: 2,476
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Re: What does a blanking signal look like?
It should be a square shouldered pulse waveform after all it is used to cut the crt off at a given transition point.
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I don't suffer from Insanity. I enjoy every minute of it. |
14th Nov 2018, 7:24 pm | #3 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
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Re: What does a blanking signal look like?
Some news just in: the tube heater isn’t glowing. That would explain the lack of display.
I tested the tube by connecting the heater pins to my bench 6.3v supply and the heater glows, so the power supply has to come out of the ‘scope again. I rather hope that one of the series resistors has failed rather than the transformer.
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Richard Index: recursive loop: see recursive loop |
15th Nov 2018, 7:14 pm | #4 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
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Re: What does a blanking signal look like?
Yes, series resistors had failed open circuit - replaced with 15ohm ¼W. Test tomorrow.
I also discovered that the RIFA capacitor in the IEC socket had gone very smelly so I’ll replace that while it’s out …
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Richard Index: recursive loop: see recursive loop |
15th Nov 2018, 10:06 pm | #5 |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: What does a blanking signal look like?
Sounds like you’re making good progress , Richard, I’m pleased to hear it.
Hopefully you’ll tie it all up soon and it will be working brilliantly!
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Al |
16th Nov 2018, 7:47 am | #6 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
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Re: What does a blanking signal look like?
Oh, I hope so. This 'scope has been un-clothed on the bench for far too long!
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Richard Index: recursive loop: see recursive loop Last edited by mole42uk; 16th Nov 2018 at 8:16 am. |
16th Nov 2018, 8:07 pm | #7 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
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Re: What does a blanking signal look like?
Yes, the screen now shows a display. It’s not yet a readable display but still means significant progress.
I’m happy that the power supply is behaving, I don’t even use the Variac any more.
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Richard Index: recursive loop: see recursive loop |
18th Nov 2018, 7:58 pm | #8 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: What does a blanking signal look like?
Quote:
Keep us updated!
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Al |
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