Electronics > Repair

Dead TDS3000B (3054B) , possibly processor?

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pcarew:
Minor update,
I've been able to trace the OE signal to a via that's under the MPC860.
Not sure I understand how/why the processor would be able to turn off it's own clock.
Still looking. I really don't want to have to pull the MPC860 BGA unless I really have to.

sicco:
I just checked on a TDS3052B board with no CPU mounted anymore. The 7Z26 buffer chip is not supplying the XPC860 with its clock. But the 7Z26 pin 2 input is tied to the same pin that the XPC860 uses for CLKIN (called EXTCLK at pad N2). The XPC also can use a crystal between its EXTAL on pad P1 and XTAL on pad N1, but that's not used. EXTAL is tied to GND, XTAL is NC.

So you will have a 25 MHz clk most likely ticking on the XPC860 EXTCLK input. Irrespective of that 7Z26 being enabled or not.

I think your next step is trying the replace that BGA with all of its 357 pins. I never succeeded - but maybe because I don't have the right tools or skills.
Before going there, maybe see if you can talk to the chip through the legacy Background Debug Mode (BDM) port. For that you need a BDM tool. The BDM pins are on the 100 pins expansion connector. Via BDM you can reset and go single step from reset, peek and poke registers, access and reprogram the flash ROM, check RAMs etc.

pcarew:
Hello Sicco,
Many thanks for your help and suggestions here.

With regard to pulling and reballing and/or replacing the MPC860 BGA, you said that you had not been successful. What process had you tried and what was your outcomes?

I have some BGA equipment, but have not yet put it to use. So, in that respect, I'm a novice and this board looks pretty densely populated  (I have replaced general SMD devices and chips in the past on other boards).

Your suggestion of the Background Debug Port sounds like a logical next step. Am I right in thinking that you detailed what is needed in a previous thread?

Thanks
Paul.

scopeman:
On that BGA you might want to contact Lou? Rossman as he has the tools to do the job and has resoldered components for other members of the group. I don't have any idea
what he would charge for such a service but he might even make a video on his channel about it. Seems like a very reasonable guy. Used to do his work in NYC but it appears
that he got out of there and moved to Austin TX.

https://rossmanngroup.com/

You can find videos of his work on YouTube and there is one where a member if EEVBLOG sent a Tek scope board up and had him swap a chip.

Found it:

https://youtu.be/JH8izpJknq0


Sam
W3OHM

pcarew:
Thanks for the suggestion.
As it happens, I live in Austin, Tx too.

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