(Solved thanks to Roland) tds210 have problem with BL section

[nic77]

Good day to all ,an wish everyone well,
i have a problem with my tds 210 , the back light is very dimm , so i opened and changed the ccfl neon ,nothing doing
,still the same , as i searched web i could not find anything ,they say there is very high voltage on the output  of the transformer , about a 1000 vac  so i cant test that ,
 I checked the transformer secondary output for continuity and got 121 ohms ,  can someone help me with this issue as i never have worked with high voltage things, i am only a hobbiest and almost on pension ,would be very pleased , greetings to all nic77 from Italy.

[RolandK]

On my Tektronix TDS 220 the ccfl was dark. One of the two transistors in the HV Converter was open collector. After replacing it worked, but there was only a very weak backlight.

So i recycled the LED strip of a dead computer monitor from the dump. I looked for one with a frame with less than 1 cm or 1/2" deep . Someone had already opened the monitor, so i only had to dismount the display. The 23" display had at the bottom a LED strip with 4 rows each with 13 LEDs in series.

• From the length i needed 9 leds and just cut them off with some scissors for metall.
• Checked voltage and polarity with a 30V Power supply and 10kOhm in series.
• Soldered the recycled wires from the CCFL to the LED.
• Glued the LED strip to the display with hot melt glue.
• Disconnected the HV Converter for the CCFL and cut the board-connection to the ccfl connector
• the leds need about 23,7 V. The power supply has at the connector to the main board 27,8 V. So i mounted a 1kohm in series at the ccfl connector to get 4mA
• I soldered a twisted pair beween the connectors which i routed the same way as the ccfl supply to have some distance from the SMPS
• On the way I marked the polarity on the LED, the wire and the board

Now my Scope has a nice LED illumination with about 4mA supply current and 1/4 W. Illumintion is a little more cool white than original.

[jpanhalt]

Just in case you don't have it, here's a link to the service manual: https://download.tek.com/manual/071049203.pdf

Not much help there, though.  No schematics.

[austfox]

I repaired the backlight for my TDS 210  last month. I had no illumination at all. Turned out it was the 2 Mosfets (from memory IRF3205s) driving the transformer.

Edit: Sorry, looks like they are C3205 transistors. I took mine from another unit (TDS 220) that has other issues.

[RolandK]

Now with pictures of the TDS 220 Power supply board:

• Connections for the LED with 1kOhm
• CCFL Converter disconnected
• Piece of LED strip

[nic77]

Thank you all very much for you help , yes i have seen many fixes but very well explained by Roland a great very well explained ,thank you Roland for your time , thank you austfox for foto of the transformer with measurements ,as one friend just gave me a 220 in bad shape so i measured the transformer and dont get the resistance in the foto so i will do the led modification as i do have a piece of led strip ,thank you all once again ,nik.