EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Kirkhaan on September 10, 2018, 04:36:49 pm
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I'm servicing a Tektronix TDS5104. Its internal display was not working (aux. display was working fine).
Before opening the housing I checked all channels and they were working fine.
The first thing I did after opening the housing is replacing the BIOS backup battery.
Also I removed all accumulated dust inside, by using compressed air.
Subsequently I started the oscilloscope (lids still open), applied the default BIOS setting and as a result the internal display is recognized and working again.
But now suddenly Ch3 and Ch4 give attached error message.
I found someone who had a similar issue back in 2009, after a power outage in their lab. See this forum topic (https://forum.tek.com/viewtopic.php?t=133338).
Before I start to troubleshoot the acquisition board, anyone an idea on what could have happened??
I mean, nothing was connected to the channels, so any overload of the channel can be excluded.
Of course the airflow inside the housing is less ideal when the lids are open. But I cannot imagine this would lead to a thermal overload (the scope was running for about 10min.)
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The termination resistor is probably very need a very hot pre-amplifier. You really should NOT work on oscilloscopes like these without an abundant airflow over the acquisition board!
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Amazing, you are right!
When I use an external fan to force airflow over the aquisition board, the error message dissapears!
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Depending on how things are ducted, it can be very important to have chassis bits in place, even if the fans aren't removed. Since you sometimes have to work on them with the top off, you need something else. I remember a video of the LeCroy factory with special fixtures that were basically just a set of fans that are held over the board you're working on with the air directed downward, for work on active boards outside of the chassis. When I've done similar work, I've propped up a box fan at an angle, so that an acquisition board flat on the table has a huge amount of air directed sort of all over it - but I'm careful to check angle and placement of the fan with a thermal camera.
It's windy to work like that, but it does keep you from cooking your expensive scope :-+
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Good learning, thanks. I will take this info account when servicing scopes!
I would expect that such crucial thing is mentioned in the service manual (https://www.tek.com/oscilloscope/tds5052-manual/tds5000-series-service-manual). But I couldn’t find it there...