Tektronix TDS 520A

[riyadh144]

Hi, so I have bought this scope for cheap a week ago, I found that the most common problem with it was the capacitors as they leak, I have cleaned both boards, and changed all the caps. But I screwed something up, that it now doesn't boot into the main screen, as it used to do its self test now it doesn't.

I have check all the voltages across the caps and they are all fine, check the voltages of the power supply also good, check for any shorts in any of the IC's, it also didn't help.

I don't know what I screwed up in but I did badly.




this is a video of it starting

https://www.youtube.com/embed/YRk4606NVnk


Edit: I forgot to say I have two caps here and there as I accidently took the pads of but they are working and this is a temp solution tell I fix it.

[k1mgy]

That switch on the upper right of your first image.  Is it in the correct position?

[Armadillo]

From the photo, don't seem like J39 jumper board is installed?

[ArcticGeek]

I don't know if this is the problem or not...but according to your photo the fan is not plugged in to the CPU board.  On these TDS5xx/6xx/7xx series of scopes the fan must be plugged in or the power supply will not start up because of the lack of load on the 24V supply.

If the fan isn't plugged in, plug it in and then retry.

[singapol]

I applaude evb149 detailed effort in helping riyadh144 but perhaps he suffered the same fate?

Anyway what's done is done so don't blame yourself...it happens. Your best frriend would 520A service manual
but be aware that some manual may not have schematics especially this model which I have tried to find.Manage to find schematic and it's broken up to particular sections maybe to shrink filesize however when I try to open them just now adobe says it can't decrypt them..damned what are people who lure people using this tactic trying to do? . So base on service manual as usual I direct you to see the troubleshooting flowchart fig.6-32 pg. 6-67. I know OP said nothing wrong with power supply but it pays to go through again as one may have missed something..overconfidence?

If power supply checks out then go on to display flowchart 6-34 pg. 6-70. This will take to some time to do for now. As the saying goes "Slow and steady wins the race." 

[JoeO]

On the second picture, the IDC cable at the bottom left of the circuit board.  It seems to be plugged in at an angle.  Maybe a bent pin?

[Jwalling]

Turn off switch #3 on the DIP switch located on the CPU board. This will make it skip a number of self tests.

[nctnico]

Find the 'TDS520B component service manual'. It tells what the number on the LED display on the CPU board means. Another problem may be the interconnect board sitting wrong. IIRC it also fits upside down and could cause this issue. The soldering on the capacitors could be much better as well.

@evb149: a few capacitors have reverse orientation compared to the rest so they may be right. Either way a reverse capacitor shouldn't prevent booting unless it is in the oscillator circuit in the acquisition board.

[StEeLz]

Hi all,

I had a lot of trouble with my TDS-520A, another one gone because of all the electrolytic juice destroying tracks.
I finally made it through by checking thousands and thousands of traces, and fixed about 30 dead traces all over the 2 boards, took me a couple of weeks (I know, why... because why not!).

Anyways, because this post is one of the top results in Google and as an EEVBlog afficionado and member, I wanted to help the community and share some of my work for anyone who would want to go through the same repair excise.

1) First finding: The original Service Manual sadly does NOT include any schematic, HOWEVER, the Service Manual for the original TDS520 Volume II has them, and it is an almost perfect identical match. Just be careful, some pages have a duplication (RAM for example) where both form factors are in the schematic, just make a note of which module yours has and discard the other half. The Service Manual is also known as "070-8313-00", for your Google search.

2) There were SO many ICs over so many pages that I started taking note of which IC corresponded to which section of the Service Manual, and has proven to be very useful, that's what I mainly wanted to share. Helped tremendously identifying and tracing.

Hope this will help womeon!

Cheers