TDS420a - Known weak spots/typical failures?


John Hudak
 

I have an opportunity to get a TDS420a that supposedly works. I haven't tried it in the flesh yet. In looking at the tek wiki and the pictures of the boards, chances of me being able to troubleshoot to the component level and actually find replacement parts, such as the xilinx FPGAs would be slim. Not like repairing older analog scopes such as the 465B or 475. Then again the onboard diagnostics might be extremely helpful.

In any case, I am wondering what the weak spots are on this scope. Insight?

Since it has a fan, and it was made in the mid-late 90's where it seems a lot of bad caps were produced, I am guessing the PS failure with leaky/bad caps is one weak spot (also given its age). Others?

Am also wondering if might be better to put the money towards a new 100 or 200mhz 4 ch Rigol instead, but thats another discussion.
Thanks
J


Brian
 

Hi 'J' , I purchased a TDS420A in a non-working state and was surprised to discover that it had been repaired not long before I got it as all the 'bad' caps had been replaced or maybe a much later produced main pcb had been fitted . The PSU was the reason for it being non-working and I replaced the caps -- it didnt cure the problem . I found a weak spot on the PSU , there is a via on the emitter trace of the switching transistor and that had failed open . No burn marks or anything to show for it but that I think was the reason for the scope not powering up . That may be a general weak spot or perhaps I was just unlucky to have that particular PSU but it is perhaps something to look out for when you are repairing the PSU .
Brian (UK)

On Friday, 13 May 2022, 21:34:43 BST, John Hudak via groups.io <uniquelogin2000@...> wrote:

I have an opportunity to get a TDS420a that supposedly works.  I haven't tried it in the flesh yet.  In looking at the tek wiki and the pictures of the boards, chances of me being able to troubleshoot to the component level and actually find replacement parts, such as the xilinx FPGAs would be slim.  Not like  repairing older analog scopes such as the 465B or 475.  Then again the onboard diagnostics might be extremely helpful.

In any case, I am wondering what the weak spots are on this scope.  Insight?

Since it has a fan, and it was made in the mid-late 90's where it seems a lot of bad caps were produced, I am guessing the PS failure with leaky/bad caps is one weak spot (also given its age).  Others?

Am also wondering if might be better to put the  money towards a new 100 or 200mhz 4 ch Rigol instead, but thats another discussion.
Thanks
J


Michael W. Lynch
 

I have two TDS460A's and have had two power supply failures. Otherwise, these have been flawless scopes. I use them almost every day. These are newer production units, built after the peak of the "capacitor plague" Boards and interiors of both units are clean, no signs of any failures of capacitors.

--
Michael Lynch
Dardanelle, AR


toby@...
 

On 2022-05-13 5:03 p.m., Michael W. Lynch via groups.io wrote:
I have two TDS460A's and have had two power supply failures. Otherwise, these have been flawless scopes. I use them almost every day. These are newer production units, built after the peak of the "capacitor plague" Boards and interiors of both units are clean, no signs of any failures of capacitors.
It's my daily driver, have had no failures yet, touch wood. Highly recommended for usability.

--Toby


John Hudak
 

Thank you all for your comments. Much appreciated.
John