Re: TDS540B Power On Self Test Pass, but changing results from SPC


satbeginner
 

Hi Siggy,

thanks for your help, sadly enough I just put everything back together again, do you still have the type of the relays written down somewhere?
I think I read about somebody writing a small tool to exercise all the relays in a long loop overnight to clean the contacts of these relays, but I agree, if they are available replacing does make sense.

I worked on my machine today again, and there is some progress I'd like to report back:

I played with the attenuators a bit, and also found a way to "revive" the contacts of them.
I removed the attenuator-assembly from the acquisition board.
Remove the front bezel, and remove the plastic partial front around the 4x BNC connector.
Now remove the 5 screws along the BNC connectors,
After that I had -to remove the Acquisition board as a whole- 6-7 screws and 3 connectors on the side and 4 little coax connectors at the back.

Turn the board over and unplug the little bandcable for the buttons by unsecuring the cable clamp first.
Now remove the 10 screws holding the attenuator assembly, and carefully lift the board from from the assembly.

At that point, one can see the 2x black plastic frames holding a lot of little golden springs.
Carefully remove the 2 plastic frames and put these on a clean piece of paper kitchen towel and soak the springs in alcohol. (in my case the springs stayed in the plastic frames)
Be careful not to loose any springs!! (I did loose 2, and had to borrow 2 from the center ground bar. There are several there and I used one from each frame.)

I used a Q-tip soaked in alcohol to clean the contact surfaces of the 4x ceramic attenuator boards.
To "revive" the springs I used a very small pair of tweezers to stretch each spring a tiny bit. (again: be careful, here's where I lost mine!)

After assembly I still had errors, but now only related to the second channel, but both DAC errors AND level related errors.

To see if things were related to the attenuator only, I dismantled everything again and swapped Ch2 attenuator with the Ch4 attenuator.
To do that I had to loosen the one center solder tab on the front of the ceramic coming from the BNC, it could be done quite easily, although they seem quite fragile.

After assembly I tested again, but now I had two channels with errors: Ch2 AND Ch4... :-)
Ch2 with DAC errors (DDataL stuck High) and Ch4 with level related errors.
So, I swapped the two attenuators back to their original places, and decided I now had a TDS530B :-)
with only Ch1, Ch3 and Ch4 working and a dead/non reliable Ch2.

For now I will start using the scope to better learn how to use it and keep an eye out for both a DAC and an attenuator or -for starters- just the relays, maybe (probably?) they solve the level related errors.
I think it must have been hurt by some overvoltage, but after all, not a bad score for two days of hobby.

Here are the additional pictures: https://groups.io/g/TekScopes/album?id=21745

Un saludo,

Leo

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