EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: 9291Sam on February 19, 2018, 08:14:51 pm
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I was watching the How to get a $50 oscilloscope video and managed to score a TDS 420 for $20 USD at a local electronics shop with one catch. It does not work. when you press the power button the Channel one Light and the "ARM" Light turn on Picture : http://prntscr.com/ih0rle (http://prntscr.com/ih0rle)
I have no idea where to start with this any suggestions?
:-BROKE
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Welcome to the forum.
Let's start with the manuals:
http://w140.com/tekwiki/wiki/TDS420 (http://w140.com/tekwiki/wiki/TDS420)
Have you used a scope before and have some good idea of how to operate one ?
What other test gear do you have to attempt a repair ?
This might help too:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf (http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf)
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Thanks for the welcome.
I have used a scope before (Only for about 5 minutes)
I have most of the other basic test equipment. Multimeter, Bench supply, Soldering Iron (Duh). ect.
( No ESR meter is the big one)
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Thanks for the welcome.
I have used a scope before (Only for about 5 minutes)
I have most of the other basic test equipment. Multimeter, Bench supply, Soldering Iron (Duh). ect.
Typically you need first ensure the PSU meets spec. Do this before anything else. Don't worry about the HV rails initially.
No ESR meter is the big one
Not so much, you can do a lot with just a capacitance meter and just flag/replace anything that's ~10% lower than spec.
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Should the power supply be good if the lights flashed on? I believed it must be a digital part of the circuit not working
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Should the power supply be good if the lights flashed on? I believed it must be a digital part of the circuit not working
ALWAYS check the PSU first. Always.
The spec is in the service manual. Take some real time to read and understand at least the basic 'Principles of Operation".
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Looking at it more the board which takes in the AC there is a 12v fan that is not spinning (the power connector is circled in the picture) http://prntscr.com/ih1lyj (http://prntscr.com/ih1lyj)
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Looking at it more the board which takes in the AC there is a 12v fan that is not spinning (the power connector is circled in the picture) http://prntscr.com/ih1lyj (http://prntscr.com/ih1lyj)
Find the PSU output test points as listed in manuals then measure them; DC and AC (for ripple) and list each one here.
Systematic approach. ;)
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Looked around in the manual and on the board and can not find any test points. or any lists of what voltages should be where
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Page 6-74 in the linked manual gives a step by step guide to troubleshooting the low voltage power supply.
Follow that methodically and you should make some progress...
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Check the boards for signs of corrosion. The TDS460 I repaired recently was FULL of leaking SMD caps. It's a common problem with devices from the early to mid 90s. The power supply also had a bunch of leaking through hold caps which caused it to shut down.
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I have looked at the board and I do not see any leaky caps. Also, everything is DIP so ...
Thanks for the Idea
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No sense in pursuing it any further if all you are going to do is just look at it and call it good.
Hint: The TDS 400 series scopes ALL suffer from the leaky caps. Some worse than others, but just a matter of time.
My TDS460 had leaky caps, but the electrolyte had long since dried after it had done it's damage, which made it harder to see in some cases.
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No sense in pursuing it any further if all you are going to do is just look at it and call it good.
Hint: The TDS 400 series scopes ALL suffer from the leaky caps. Some worse than others, but just a matter of time.
My TDS460 had leaky caps, but the electrolyte had long since dried after it had done it's damage, which made it harder to see in some cases.
I came to the same conclusion but waited for someone else to post about it. I don't understand where this person is coming from.
He takes no advice and he is looking for a quick fix.
You are wasting your time, answering this person.
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Hi, what is the value of the tantalum capacitor on the underside power supply pcb (hybrid pin 13-19).
Thanks