Author Topic: Need Tektronix TDS220 firmware file  (Read 4153 times)

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Offline Vorlon

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Re: Need Tektronix TDS220 firmware file
« Reply #25 on: July 12, 2019, 10:30:48 am »
The same happened on my TDS220 with an Aliexpress LCD.
It seems they sell defective LCDs as "used ones".
 

Offline Nprod

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Re: Need Tektronix TDS220 firmware file
« Reply #26 on: July 12, 2019, 08:42:31 pm »
I'm not sure if you can consider them defective or not, but the one i got certainly looked like it had been rusting away in a warehouse somehwere for a good 20 years. Even though both are labeled "LM32P073" there were differences in their PCBs - the original had about 3 small electrolytic capacitors on it while the aliexpress one has about 9, and they're bigger. There are also some differences in how the backlight bulb is housed. If i had to take a guess i'd say they're different revisions of the same model. Can you say which type the original and replacement screens were?

Perhaps these particular versions are designed for slightly lower contrast voltages, so a little resistor between the flex cable and PCB pad could bring it down to a more usable range that doesn't require you to set the contrast to 0% in the menu to make things visible.
« Last Edit: July 12, 2019, 08:54:07 pm by Nprod »
 

Offline JFJ

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Re: Need Tektronix TDS220 firmware file
« Reply #27 on: July 12, 2019, 09:55:18 pm »
... The LCD itself is not factory original, i got it from some old stock warehouse on aliexpress and it requires a low contrast setting to look correct for some reason...

It may be informative to compare the contrast control voltage range of your substitute LCD panel, with that of an original:

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.
 

Offline Nprod

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Re: Need Tektronix TDS220 firmware file
« Reply #28 on: July 14, 2019, 03:45:01 am »
@JFJ

Here's what i got:

Without a module installed:
SettingVoltageAppearance
0%-18.8VGood
15%-17.77VPoor contrast, display flips
50%-16.16VBlank screen
100%-13.55VBlank screen

With a module installed (TDS2MM firmware):
SettingVoltageAppearance
0%-18.5VGood
15%-17.71VPoor contrast, display flips
50%-15.94VBlank screen
100%-13.45VBlank screen

As you can see, the module doesn't affect the contrast voltage by a significant amount and the screen's response is the same. The reason i got a blank screen when first installing the module is because the scope's setting reset itself to 50%, not because of a voltage drop. Changing the EPROM possibly made the scope think it's a different module.

About the contrast - the datasheet for the LM32P07 (attached) states in its electrical characteristics (Table 4) that the contrast adjust voltage should be between 17.5V and 25.5V, with a typical setting of 21.5V. That would mean that the LCD is acting as it should, but the voltage the scope provides is too low.
 


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