tektronix tds1012b led backlight retrofit

[gimp-e]

Hi guys,

This is my first post. i aquired a tektronix tds1012b oscilliscope from an electronix recycler. The scope works, but after about 20-30 minutes, the screen goes black. After some research, it seems the CCFL backlight bulb goes out, and replacement bulbs aren't available. So, I'm in the middle of an LED retrofit for the backlighting as detailed on this site:

https://nt7s.com/2016/05/tds1012-led-backlight-retrofit/

In order to do this, I need a schematic of the tds1012b. Does anyone happen to know where I might get one? (I especially need the power supply section...)

thanks in advance.

Cheers!

[tautech]

Welcome to the forum.

Depending on the voltage your LED backlight needs it shouldn't be hard to find the voltages you need on the PCB although current requirements need be considered before you hook onto just anywhere.
Check the service manual for the PSU header voltage assignments.
You can get the manuals here:
http://w140.com/tekwiki/wiki/Main_Page

Have a look at this one that Shahriar did:

https://youtu.be/smrMoIpvYTk

[gimp-e]

Thanks for the reply! I already had both the user manual and service manual, but neither has a schematic. In the retrofit article that I'm trying to replicate, the author says he soldered to a 6V rail on the J9 connector of the PCB (which I will look at tonight), but I don't show that L9 connector anywhere in either manual. The service manual shows the main ribbon cable (J101), but no info on voltages, which is why I'm trying to find a schematic. Since I'm a newbie, I'm a little nervous to just go poking around blind with a multimeter inside this thing while it's on, since the goal is to repair and use it, not fry it.

[tautech]

Is you look carefully at the pics of the Tek PSU I'm quite sure the rail voltages are listed in the PCB silkscreen next to the cable header. Unplug it and continuity test to the mainboard to find the 6V rail so to find a suitable pick off point for the LED backlight driver.
If you're still worried that it's not the right point, mark it with a sharpie and connect it together again, power it then measure it with a DMM.
You shouldn't need a schematic only open eyes and a clear head. 

Tell us how you get on. 

[gimp-e]

Thanks for the reply. I'm looking at it tonight after work, so hopefully I can find a place to solder the wires for the boost/buck converter. I want to do some more testing on that circuit before I wire it in, just to get the amp draw from the circuit as low as possible so I don't (hopefully) overload the circuitry in the scope.

[tautech]

Thanks for the reply. I'm looking at it tonight after work, so hopefully I can find a place to solder the wires for the boost/buck converter. I want to do some more testing on that circuit before I wire it in, just to get the amp draw from the circuit as low as possible so I don't (hopefully) overload the circuitry in the scope.

You may have to remove the scope mainboard to get a good point to connect the LED supply but try and select a point close to the PSU cable header so not to inject any noise into the scope circuitry. You might also want to look at disabling the CCFL supply HV generation as it's no longer needed. Just slicing the right trace might be enough. 

[gimp-e]

Ok. I'll give it a go...

[gimp-e]

Boy, tautech, you know your stuff! I took a close look at the silkscreen on the power supply board and Viola! There's the 6V supply! (1st photo) It also conveniently had some jumpers going across a ground plane (I think). When I looked at the bottom of the PS board, it looks like I can solder the + for the boost converter directly to the bottom of the jumper. There are several pins on the PSU header labeled "COM", which I'm guessing are grounds, judging from the fact that they go to the "ground plane". Could you look at the second photo (if you have time) and tell me if my assumption is correct,please?

[tautech]

Boy, tautech, you know your stuff! I took a close look at the silkscreen on the power supply board and Viola! There's the 6V supply!

Nah, just spotted the silkscreen in the link you provided: https://nt7s.com/2016/05/tds1012-led-backlight-retrofit/
Pretty normal setup to have the PSU rail voltages marked on the PCB. 

(1st photo) It also conveniently had some jumpers going across a ground plane (I think). When I looked at the bottom of the PS board, it looks like I can solder the + for the boost converter directly to the bottom of the jumper. There are several pins on the PSU header labeled "COM", which I'm guessing are grounds, judging from the fact that they go to the "ground plane". Could you look at the second photo (if you have time) and tell me if my assumption is correct,please?

Very likely but always do a sanity check to see if the COM's are all linked.....DMM continuity test.
As there's 5 supply rails the current return path needs be shared amongst a few pins....again, a pretty normal setup.
Now you need find a spot to connect to COM....is an eye terminal under a PCB screw possible.....see the exposed solder on the underside of the PCB ? Is that COM ? Check with a DMM.

As the JP3 link is your 6V target connection I'd just tin it well and wrap a tap off wire onto the middle of the link and on the topside of the PCB.
Why there ? Probably no more rigid/strong connection spot unless you drill a hole in the PCB and feed the wire down and under for an underside joint/tap.

[gimp-e]

Spot on advise. Yes, an eye terminal under the PCB is both possible AND convenient, Also, tinning and wrapping a wire on that 6V jumper wire is also both possible and convenient. I'll just put something under the jumper wire to catch any solder if it drips. I'm hoping to get to this over the weekend, but I'm also in the middle of an electronic ignition conversion on my 40 year old Toyota!

We'll see how it goes....

Thanks for all the help and advise. I'll let you know how it turns out.....

[gimp-e]

IT'S ALIVE!!!

I managed to successfully install the LED and boost converter, wired ground to a PCB mounting post, and soldered to the 6V jumper on the PCB. Fired the old girl up and viola!
(See photos). I still need to mount the boost converter PCB (I'll probably use silicone, as there aren't any mounting holes on it), but it works. One weird thing, though:
When I first turned it on, it said, "Unknown signal on channel 1" and the normally horizontal straight line was a little fuzzy and wavy. It went away after doing the self-calibration, though. Any thoughts on what that might be?
So, I'm going through the manual, step by step. Got the self-calibration done, and got the probes calibrated ( I ran them thought the probe check Wizard, and they passed)
So far, so good. Looks like it might be a good working scope!

Thanks to everyone for their help. Special thanks to tautech for the suggestions on where to connect the boost converter. It made the job a lot easier.

[bd139]

Cool stuff. Going to do this with my TDS210 when the CCFL gives out.

[tautech]

You're welcome gimp-e, thanks but you did all the work....I just kept prodding you in the right direction. 

A TDS2012B was my first DSO and while it's busted now you can learn/do most of the basics with them even though the more modern DSO is capable of a heap more.

Anyways, what I get a kick out of this is what you've learned which one would suspect will launch you into repairing and building more things for yourself. 

[gimp-e]

Thanks! The idea is to use it to circuit trace the power supply on my Kurzweil RG200 electronic keyboard an try to get it fixed this winter, then JAM!