Tektronik TDS220: transformator dead - Page 1
Forum section: electronics / repair

author: Bubzy
author_rank: Newbie
timestamp: January 29, 2025, 01:29:43 pm
content: Hello!I got a TDS220 6 months ago, It had backlight issues and loose BNC. But it worked (the screen turned on etc).I put it on a shelf until I had time to take care of it.This week I finally purchased the parts to fix it. (I didnt retest it before)I did what i was supposed to do but in the end, I got a black screen.After some investigation the power supply have issus (the highest voltage i got was 2V).The transformator '3012585 Ault Korea' have its secondary part all shortcut (and It make very strange noises).I desoldered it to be sure and measured 0between some secondary pins.What can I do now?'3012585 Ault Korea' have no datasheet, I can't find another one until I dont know the voltage output. I hope someone can help me find a replacement.The power supply (P119-5417-00) is verryy expensive, I dont want to buy a new one.Could I repair the transformator? Can I redo the isolation and the coil winding? (How?)Notice that I'm doing it for fun, I already have another oscilloscope.Thanks for your help,If you need more information, let me know =)

author: CaptDon
author_rank: Super Contributor
timestamp: January 29, 2025, 01:58:01 pm
content: The secondary windings will measure in the milliohm range, do you have a meter that can accurately measure milliohms? The problem is that you probably created a short on one of the power rails during your repair. The transformer will indeed make weird noises if try to energize power into a short. The transformer is the very last thing I would suspect as being the problem.

author: tunk
author_rank: Super Contributor
timestamp: January 29, 2025, 02:09:27 pm
content: No expert on this: If the transformer still is out, do any of the secondaries show a short?

author: Bubzy
author_rank: Newbie
timestamp: January 29, 2025, 09:31:32 pm
content: Sorry, I forgot to mention some of tests i did:I tested to solder only the primary part and not inserting secondary pins in their holes (secondaries isoleted of the circuitboard) and the noise was even worse.Without the transformer, the circuitboard have no shortcut (in secondary and primary part)Notice that in all my tests, the power supply was not connected to the main board.Quote from: CaptDon on January 29, 2025, 01:58:01 pmSorry! I retested the measures in ohm mode, at the first time I was in the continuity mode (the beep mode)My meter have a 10mOhm resolution.(edit: the measurements were unusable, the image was removed)I recorded all resistances between pins in the attached image.Quote from: tunk on January 29, 2025, 02:09:27 pmSo with the new measurements there is no 0ohm, so no short. But overloaded measure are not a good sign either?Quote from: CaptDon on January 29, 2025, 01:58:01 pmThe repair was not complex. I dont really know how i could have damaged the power supply, especially since i have barely touched it...Quote from: CaptDon on January 29, 2025, 01:58:01 pmI'm surprised too that transformer could be in default. I will be happy if it could be something else...What other test could I do?

author: George Edmonds
author_rank: Frequent Contributor
timestamp: January 29, 2025, 11:31:58 pm
content: HiPlease save me from idiots, how to test a mains transformer should be part of basic electronics lesson 101.IN1 to IN4 are two 115VAC windings used in phase series to give 230VAC in.Secondary,This table is nonsense,01 to 05 on line 1 is 30 Ohms01 to 02, 03, 04, 05 is open circuit, line 2. How is this possible?DC resistance measurements of transformer windings tell you absolutely nothing as a transformer is an AC only device.Testing a mains transformer is simple, especially one with only two secondary windings. BUT you need a good knowledge of electrical safety which appears to be sadly lacking here.G Edmonds

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 29, 2025, 11:57:55 pm
content: Your transformer measurements make no sense, do the measurements again.Resistance measurements will only tell you the basic pinout androughlywhich windings have more turns than others (but not turns ratio or anything precise at all), assuming the transformer is working.Tell usexactlywhat repairs you did, down to the exact components you replaced. I suspect something strange has happened with the backlight repair...

author: Bubzy
author_rank: Newbie
timestamp: January 31, 2025, 09:25:46 pm
content: Hi!Quote from: George Edmonds on January 29, 2025, 11:31:58 pmYou're being rude, but you're right, I rushed my measurements and made mistakes. I appreciate you taking the time to point that out.By the way, I usually work with digital electronics, not power electronics. That's why I may lack experience in testing transformers and power supplies.It makes no sense to be this condescending on a platform built on mutual help where I'm supposed to be learning.Also, I’m fully aware of the dangers involved, and I always take great care when handling high-voltage components (At least, I hope so?).QuoteI feel very dumb...I redid the measurements properly, without being tired and by taking my time.I did them closest to the coils, which's why the resistance values are different.Resistance measurements can help determine if the coils or the insulation are damaged right?Quote from: TERRA Operative on January 29, 2025, 11:57:55 pmI only replaced the CCFL lamp, and 3 BNC connectors.The new CCFL lamp had a different connector so I cut it and soldered the old connector onto it.It's basically just unplugging the old lamp and plugging in the new one.I found someone who did the same repairs in a video: (at 13:28 and 15:48)Thanks for your patience!

author: MrWoo
author_rank: Newbie
timestamp: July 30, 2025, 10:41:16 am
content: You showed In as 4 terminals, two of those are supply to the voltage regulator controlling the mosfet.C6 is probably the problem. Maybe change all electrolytics.I've been reverse engineering the circuit to repair my unit.The service manual shows voltages at J131.

author: d-el
author_rank: Regular Contributor
timestamp: July 30, 2025, 10:47:05 am
content: Quote from: Bubzy on January 31, 2025, 09:25:46 pmWhat kind of tester is this connected to the BNC?This is not the first time I've seen this.

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 30, 2025, 10:49:14 am
content: An older model of the Leo Bodnar pulse generator.