Tektronix TDS 224 Display Repair

[gblack3003]

Hello all, so I must apologize and say at first I'm a complete noob at this.  I'm electronically inclined but not amazing with this.

So I recently was diagnosing a Tektronix TDS 224 I came across with a dim/dark screen.  Everything pointed to repairing the screen, so I bought a replacement screen.  The new one came in and I swapped it out w the old, plugging in the new screens backlight (red and white wires) and plugging in the cable where the old cables and backlight used to be.

And it works now!  The screen stays lit perfectly, the only thing is that the colors are inverted!  Like I said I'm a noob, so I'm guessing I accidentally swapped the wires somewhere?  What would cause the display to be "inverted" basically (where light colors are black and where the black is light). 

I'm guessing I'll have to take it apart and swap the ribbon cable 180 degrees, or does this make sense?  Thank you for the help in advance!

[Muttley Snickers]

I have a TDS-1002 which are sort of similar and the screen display can be inverted in the setup menu, it's probably best to confirm this settings selection first before going any further.    

[gblack3003]

Thank you for the reply! Is there a settings menu for setup separately from what you access after it is booted? I have messed with save/recall settings and display settings and still can't find this anywhere! How do you change the inversion on yours? Here is a picture of my layout

[Muttley Snickers]

On the TDS-1002 you only need to press Utility – Options – Display Style and then select from either Normal or Inverted, I expected the TDS-224 to be similar but after having a quick look through both manuals there is nothing I could see that explains this in any detail. There is also a hidden systems menu on most of these scopes but you will not need to go there and probably shouldn’t ever need to anyway.

Utility > Options > Display Style > Normal/ Inverted   

[JFJ]

The screen stays lit perfectly, the only thing is that the colors are inverted!

It looks like the display's contrast is set too high. Unless there's a hardware fault, you should be able to return the display to black-on-white by simply reducing its contrast (using the 'Contrast Decrease' button, from the 'Display' menu).

[jpanhalt]

I have a TDS210 and concur with JFJ.   Go to Display menu and try adjusting your contrast.   "Utility" will not get you to the answer.  There is an "invert," but that applies to the math button, which inverts the waveform.

BTW, I will not part with my old TDS despite having a new Rigol with a lot of bling.  I still use it when looking for transients -- and it is silent.

John

[Muttley Snickers]

It looks like you guys might be right and I only assumed from the first posted pictures that the OP had already adjusted the contrast without success, as I mentioned the TDS-1002 does have the ability to directly invert the display in addition to contrast adjustment so figured they were probably similar as it looked to be inverted.

I did find this link earlier were somebody else had replaced the screen on a TDS-220 and then needed to go into the setup menu to make further adjustments that perhaps were now out of range for the normal contrast setting, anyway a link and picture below just in case. 

http://laredohackerspace.blogspot.com.au/2013/05/workaround-to-get-extra-contrast-on.html

[gblack3003]

The screen stays lit perfectly, the only thing is that the colors are inverted!

It looks like the display's contrast is set too high. Unless there's a hardware fault, you should be able to return the display to black-on-white by simply reducing its contrast (using the 'Contrast Decrease' button, from the 'Display' menu).

Yes this was one of the first things I tried, unfortunately changing contrast does not work. The colors are still inverted, when I go to high contrast all the darker parts just turn darker and vice versa.

I think the Mfg Test > Inc Contrast might work however it is acting strange. Whenever I go into the service menu and press any button within the Mfg Test menu the screen turns completely blank and nothing happens unless I turn it off and turn it back on! I read a lot about the servicing last night and still can't find a solution

[Fraser]

Thanks for the link to the service menu contrast menu. Very useful

Fraser

[gblack3003]

It looks like you guys might be right and I only assumed from the first posted pictures that the OP had already adjusted the contrast without success, as I mentioned the TDS-1002 does have the ability to directly invert the display in addition to contrast adjustment so figured they were probably similar as it looked to be inverted.

I did find this link earlier were somebody else had replaced the screen on a TDS-220 and then needed to go into the setup menu to make further adjustments that perhaps were now out of range for the normal contrast setting, anyway a link and picture below just in case. 

http://laredohackerspace.blogspot.com.au/2013/05/workaround-to-get-extra-contrast-on.html

And yes thank you for all the help! I think I'm going to call the customer service for Tektronix on Monday or Tuesday when a I get a chance to see if there is another solution since the enhance/decrease contrast options are not working.  Could be the replacement screen I ordered too... Either way I will keep you guys updated on the solution when I get it.

[Fraser]

My TDS 1000 series scope has the invert LCD 'colours' option as has been mentioned. I did not see confirmation that this had been checked on the OP's Scope. Mines looks like the OP's display when the Display is set to white on black mode (inverse)

Fraser

[Muttley Snickers]

The other members that have closer series scopes did indicate that the invert screen option that we have on ours is not present on the TDS-200 series and is limited to the contrast adjustment only. I had a bit of a look around but couldn't find any information on a TDS-224 inverted screen issue so this one is a bit of a mystery, I did however find some very interesting stuff in relation to improvements which can be made and may be useful for others with similar backlight or screen problems.

TDS-1012 LED Backlight Retrofit.
http://nt7s.com/2016/05/tds1012-led-backlight-retrofit/

Replacing an LCD CCFL Backlight (TSD-210 Scope).


   

[gblack3003]

My TDS 1000 series scope has the invert LCD 'colours' option as has been mentioned. I did not see confirmation that this had been checked on the OP's Scope. Mines looks like the OP's display when the Display is set to white on black mode (inverse)

Fraser

Yes I looked meticulously into this Fraser and definitely doesn't exist on mine. Hopefully tektronix can help me with a more difficult problem. The only invert options I have are related to signals not colors

And very very helpful video!! Glad you posted that. That's what I think I needed to do and I could've had a $10 dollar repair instead of an $80! Still wasn't sure so I just replaced the whole display. But that is exactly how you would replace the CCFL tube in the 224 too if anyone comes here later wondering.

[JFJ]

I think I'm going to call the customer service for Tektronix on Monday or Tuesday when a I get a chance to see if there is another solution since the enhance/decrease contrast options are not working.

Before contacting Tektronix, you might take a voltage reading that could help to determine cause of the problem. The LCD contrast is set by the voltage that is applied to the first conductor of its ribbon cable (for a TDS210/TDS220, conductor 1 is at the edge of the ribbon that is nearest to the rear of the oscilloscope).

On my TDS220, the Contrast buttons adjust the voltage on conductor 1 between -13.1V and -19.0V. The effect of this varying voltage is as follows:
 
-13.1V = A negative display (white-on-black)
-16.7V = A normal display (black-on-white)
-19.0V = A white display (completely washed out)

(the voltages are with respect to the main board ground connector).

NB With the ribbon cable only partly inserted into its connector (just enough to engage the contacts), sufficient conductor protrudes above the connector to take voltage measurements with a standard DMM probe.

[Fraser]

JFH,

That is useful information that I will file away as I have a TDS220 as well 

Thank you

Fraser

[Nprod]

The service menu really helped to get my replacement screen to look right, but when i leave the service menu or turn the scope off, anything i set gets reset. Is there any way to have it store the service menu's contrast settings? The new screen looks best at about -19.2V but i can't get it to go above -18.9V with the regular contrast adjustment menu.