Tektronix TDS684 - Flyback Transformer 120-1930-00 - Page 1
Forum section: electronics / repair

author: Armadillo
author_rank: Super Contributor
timestamp: April 09, 2016, 12:43:22 pm
content: Hi, Good day all;Need advise from you;Had the oscilloscope completely dark screen. The fuse on the display assembly didn't blow. The flyback secondary open circuited.Is there any replacement parts for the flyback or equivalent replacement?I thought alternative fix would be a separate +75v and -75v transformer mounted somewhere. Anyone tried some magic before?thanks;

author: nctnico
author_rank: Super Contributor
timestamp: April 09, 2016, 12:53:50 pm
content: Usually the flyback transformer also supplies other voltages. Your best bet is to hunt Ebay for a replacement board or get an LCD screen replacement. Also be aware that some of the TDS600 models (IIRC the A series) don't have peak detect which makes using them as a general purpose scope a bit problematic because you'll be missing narrow spikes quickly at lower samplerate settings.

author: Armadillo
author_rank: Super Contributor
timestamp: April 10, 2016, 01:26:40 pm
content: Hi Guys;No luck so far.I would have to wind the flyback myself, I think.!So at the moment, I would have to make do with a big screen TDS684 Oscilloscope.Anyone has experience on winding high voltage flyback transformer? Please advice. thanks;

author: eeadata
author_rank: Contributor
timestamp: April 10, 2016, 06:51:55 pm
content: Upgrade it with an lcd retrofit kit.

author: tautech
author_rank: Super Contributor
timestamp: April 11, 2016, 08:02:22 am
content: Try Sphere.They don't appear to have the one you want ATM but you should contact them anyway.http://www.sphere.bc.ca/test/tek-transformers.html

author: Jwalling
author_rank: Unknown
timestamp: April 11, 2016, 10:48:58 am
content: Quote from: Armadillo on April 10, 2016, 01:26:40 pmWhere are you located? You should update your profile with your location so folks won't have to ask.I have a bunch of these HV assemblies from doing LCD conversions. If you're in the US, I could sell you one for reasonable $.Jay

author: Armadillo
author_rank: Super Contributor
timestamp: April 11, 2016, 12:38:09 pm
content: Quote from: tautech on April 11, 2016, 08:02:22 amThanks for direction, I have written to them, my finger crossed.

author: Armadillo
author_rank: Super Contributor
timestamp: April 11, 2016, 12:47:01 pm
content: Quote from: eeadata on April 10, 2016, 06:51:55 pmThanks, It's a pretty good idea, actually.... but you are not suggesting "NewScope" are you?

author: nctnico
author_rank: Super Contributor
timestamp: April 11, 2016, 04:46:49 pm
content: I'd jump at Jwalling's offer! Replacing the CRT driver board is the easiest fix by far even if it takes a sugar coated pretty 'please' with cherries on top for asking to ship outside the US if necessary.

author: Jwalling
author_rank: Unknown
timestamp: April 11, 2016, 06:58:37 pm
content: Quote from: Armadillo on April 11, 2016, 12:47:01 pmNice bit of kit, I've done one of those for a customer, but $350 + shipping to Singapore.Jay

author: Jwalling
author_rank: Unknown
timestamp: April 11, 2016, 07:01:41 pm
content: Quote from: nctnico on April 11, 2016, 04:46:49 pmHe's already contacted me by PM. I told him that I'd sell one for $85USD + shipping, but shipping to Singapore USPS would be $68.Almost the cost of the assembly.

author: Armadillo
author_rank: Super Contributor
timestamp: April 17, 2016, 12:54:23 pm
content: Hi, good day my friends;Something is really puzzling me [See picture attached]. The high voltage winding has an internal resistor at pin 12 used for feedback to high voltage control circuit. I measured using the highest ohms range, red probe on pin 12 and black probe on pin 10 and there was infinity reading. The ohm seems too high for a multimeter to measure. So I jacked in 60VDC [current limited] across pin 12 and pin 10 hoping to see some current flowing through thus by simple ohms law could deduce the resistor value. But, the current read zero. It seems the resistor is open circuited OR something I don't understand. Could some good friends out there, if you have the transformer conveniently lying around, measure the value. Thanks in advance.I measure the feedback capacitor its 100pF and the other filter capacitor 2nF. But if the wire leading into pin 12 is open, those readings are doubted.In the service manual, the horizontal sync looks like 100 KHz, this is used to switch the transformer. Something new to me, cause I had never seen video signal with horizontal sync at 100KHz!!Yes, I am meddling with the transformer. This is part of the fun of learning electronic. Thanks for reading.

author: Jwalling
author_rank: Unknown
timestamp: April 17, 2016, 02:07:56 pm
content: Quote from: Armadillo on April 17, 2016, 12:54:23 pmLooks like about 32KHz to me.Will check a transformer in a bit...Whatever it is, it's greater than 100M Ohm so my Keithley 2000 won't measure it.Jay

author: nctnico
author_rank: Super Contributor
timestamp: April 21, 2016, 08:57:42 pm
content: Quote from: Armadillo on April 17, 2016, 12:54:23 pmThat is because the color video in the TDS500/600/700 series runs at 180 frames/s (3x60Hz) in order to display a red, green and blue image sequentially while maintaining a 60Hz overall refreshrate.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 21, 2016, 10:16:07 pm
content: Just to make sure, you know that the Vf of those high voltage diodes is often quite high since they just stack up a bunch of regular diodes to make them?I'm worried you're barking up the wrong tree thinking the secondary is open when it's not.

author: nctnico
author_rank: Super Contributor
timestamp: April 21, 2016, 10:24:01 pm
content: On the image with the signals it says 'monochrome display'. Don't use the schematics for the monochrome display section for a color scope because they are very different! Chances are the windings are on different pins.

author: Armadillo
author_rank: Super Contributor
timestamp: April 24, 2016, 03:48:15 pm
content: Quote from: Paul Moir on April 21, 2016, 10:16:07 pmHi Paul, thanks for the reply. The secondary that was open circuited is the +75volts winding, not the HV winding. The +75volt is very essential for this display board to function.For those that are interested, I have managed to measure the ohms of the HV feedback resistor. It is 300 Mega Ohms [you cannot measure with multimeter]. This resistor alone is not cheap, you can check ebay. During the course of it, I have learnt a couple of things. For example the HV windings in wound in a special bobbin that separates it into many sections so that internal arching can be avoided.Actually, I have already installed with LED TFT screen, high resolution. As it turns out, a piece of cake and the display is very vividly sharp and clean and I have come to accept it, though, you know, the feeling that the scope is no longer the original... But as it saves a whole lot of space, reduce heat and current consumption, I would recommend the upgrade to LED screen actually.But I will continue to wind the HV transformer out of interest and build a special winder to tackle the 0.02mm magnet wire. The cost would not add-up, if you ask me... Cheers!