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Old 1st Apr 2018, 4:04 pm   #1
ftingle
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Default Telequipment D1011 blows mains side fuse

Hi all,

I picked up a telequipment D1011 o-scope and it blows the 400ma fuse before the toloidal transformer.

Looks like the transformer T401 has packed it in as when I isolate it from the bridge rectifier, the fuse still blows.

Q: What should be the output of the transformer (VAC) to provide 22vdc? I'd like to see if I can find a replacement. It's been too many years since I've had to do the maths. Otherwise, anyone have one in your junk boxes?

Attached is screen shot of ps circuit.

THX! Frank
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Old 1st Apr 2018, 6:38 pm   #2
TonyDuell
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Default Re: Telequipment D1011 blows mains side fuse

Quote:
Originally Posted by ftingle View Post
Q: What should be the output of the transformer (VAC) to provide 22vdc? I'd like to see if I can find a replacement. It's been too many years since I've had to do the maths. Otherwise, anyone have one in your junk boxes?
With a bridge rectifier, the output voltage is sqrt(2) * the RMS transformer secondary voltage. So to go the other way you divide by sqrt(2) (=1.4142 to enough accuracy for this).

For a 22V output you need a 15.5V (or so) transformer. I would guess a 15V one would be fine.

But what bothers me is that tap-changing switch on the secondary side of the transformer. What is that for? I understand the series/parallel switch on the mains side for 230V or 115V mains of course.
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Old 1st Apr 2018, 7:16 pm   #3
karesz*
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Default Re: Telequipment D1011 blows mains side fuse

Tony,
you corrects with S403 a little bit (+/-10%?) mains deviations from nominal values...
rgds, Karl
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Old 1st Apr 2018, 7:29 pm   #4
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Default Re: Telequipment D1011 blows mains side fuse

The switch on the secondary is marked high/low and is for high/low mains respectively.

I suspect that this is a 20Volt transformer

Part crossed with Karl

Cheers

Mike T
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Old 1st Apr 2018, 7:33 pm   #5
TonyDuell
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Default Re: Telequipment D1011 blows mains side fuse

Thanks...

Yes, for a 29V output you need a 20V (or so) transformer. But the OP said 22V. Which is is really?
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Old 1st Apr 2018, 7:55 pm   #6
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Default Re: Telequipment D1011 blows mains side fuse

22V is one of the regulated supplies, its the one you set up and adjust.

Cheers


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Old 1st Apr 2018, 8:18 pm   #7
buggies
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Default Re: Telequipment D1011 blows mains side fuse

Just a quick check to confirm that the fuse is a delay type?
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Old 8th Apr 2018, 11:50 am   #8
Skywave
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Default Re: Telequipment D1011 blows mains side fuse

There is a slim chance that the 115-v. / 230-v. switch may be faulty, effectively arranging the transformer windings (pri. and / or sec.) for 115-v.
The way to test that possibility is to temporarily wire the transformer so that the switching is no longer in the cct., with 230-v.a.c. on the pri. and with the sec. on N/L. To do that, it might be easier to completely remove the transformer completely from the chassis. If the transformer does then prove to be U/S, you've not wasted your time in so removing, since you will then know it has to be replaced anyway.

Al.
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