SMPS chopper transformer. - UK Vintage Radio Repair and Restoration Discussion Forum

paul farn · 11th Aug 2023, 10:22 am

Can a chopper transformer be tested for shorted turns? Got a LOPT tester courtesy TV mag but would it work on above? Probably not.
P.

TonyDuell · 11th Aug 2023, 10:27 am

I've used a ringing tester built from Television magazine to test chopper transformers. It seems to pick up shorted turns OK, as you might expect. After all, it just shows that the oscillations are heavily damped due to the energy absorbed in the shorted turn.

toshiba tony · 11th Aug 2023, 12:40 pm

Might be related but I used to "ring" lopts. Just attach the two top connections to check line output transformers. If you got EHT on the primary you could assume the transformer was good, never let me down.

paul farn · 12th Aug 2023, 10:44 am

Quote:

Originally Posted by TonyDuell

I've used a ringing tester built from Television magazine to test chopper transformers. It seems to pick up shorted turns OK, as you might expect. After all, it just shows that the oscillations are heavily damped due to the energy absorbed in the shorted turn.

Have you got a copy of this cct?It sounds like the right device for the job.I would think you also need a 'scope to view.Is that right?
P.

Graham G3ZVT · 12th Aug 2023, 11:57 am

To get this shot, I think I simply had one probe on the Y input and the other on the Cal output and connected them across the primary winding of the Loptx I was testing.

paul farn · 17th Nov 2023, 11:06 am

Applied ringing test to device as described ie:cal-winding-i/p.Acceptable trace obtained similar to above.
Power diode shorting on sec which I should've checked earlier.Could've saved ages.Ah didnae ken.
Put it all back together & not a bad picture considering tube is 38,TX 100 series.Is this a record?
A few other components want replacing sometime.....

its ur aerial · 17th Nov 2023, 11:57 am

That Diode was a common fault back in the day, was it D22, a BY298

memory fading.

Ken G6HZG.

paul farn · 20th Nov 2023, 11:34 am

Quote:

Originally Posted by its ur aerial

That Diode was a common fault back in the day, was it D22, a BY298

memory fading.

Ken G6HZG.

It was the other one actually.D15(byw74).
P.

its ur aerial · 21st Nov 2023, 7:24 am

Paul, thanks for jogging the memory

Ken G6HZG.

Radio Wrangler · 21st Nov 2023, 9:10 am

All transformers can be tested by a ringing technique, though sometimes you may need to add a capacitor to get a ring frequency you can use. Interpretation might be best by comparison with a known good one. For RF transformers you need a fast-edged pulse generator and a fast scope or a TDR.

David

11th Aug 2023, 10:22 am	#1
paul farn Triode Join Date: May 2023 Location: Epsom, Surrey, UK. Posts: 30	SMPS chopper transformer. Can a chopper transformer be tested for shorted turns? Got a LOPT tester courtesy TV mag but would it work on above? Probably not. P.

11th Aug 2023, 10:27 am	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,066	Re: Don't know I've used a ringing tester built from Television magazine to test chopper transformers. It seems to pick up shorted turns OK, as you might expect. After all, it just shows that the oscillations are heavily damped due to the energy absorbed in the shorted turn.

11th Aug 2023, 12:40 pm	#3
toshiba tony Heptode Join Date: May 2006 Location: Accrington, Lancashire, UK. Posts: 970	Re: Don't know Might be related but I used to "ring" lopts. Just attach the two top connections to check line output transformers. If you got EHT on the primary you could assume the transformer was good, never let me down.

12th Aug 2023, 11:57 am	#5
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,588	Re: SMPS chopper transformer. To get this shot, I think I simply had one probe on the Y input and the other on the Cal output and connected them across the primary winding of the Loptx I was testing. Attached Thumbnails __________________ -- Graham. G3ZVT

17th Nov 2023, 11:06 am	#6
paul farn Triode Join Date: May 2023 Location: Epsom, Surrey, UK. Posts: 30	Re: SMPS chopper transformer. Applied ringing test to device as described ie:cal-winding-i/p.Acceptable trace obtained similar to above. Power diode shorting on sec which I should've checked earlier.Could've saved ages.Ah didnae ken. Put it all back together & not a bad picture considering tube is 38,TX 100 series.Is this a record? A few other components want replacing sometime.....

17th Nov 2023, 11:57 am	#7
its ur aerial Hexode Join Date: May 2009 Location: Ryde, Isle of Wight, UK. Posts: 406	Re: SMPS chopper transformer. That Diode was a common fault back in the day, was it D22, a BY298 memory fading. Ken G6HZG. __________________ Life is not Hollywood, life is Cricklewood.

21st Nov 2023, 7:24 am	#9
its ur aerial Hexode Join Date: May 2009 Location: Ryde, Isle of Wight, UK. Posts: 406	Re: SMPS chopper transformer. Paul, thanks for jogging the memory Ken G6HZG. __________________ Life is not Hollywood, life is Cricklewood.

21st Nov 2023, 9:10 am	#10
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,258	Re: SMPS chopper transformer. All transformers can be tested by a ringing technique, though sometimes you may need to add a capacitor to get a ring frequency you can use. Interpretation might be best by comparison with a known good one. For RF transformers you need a fast-edged pulse generator and a fast scope or a TDR. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done