Dead TDS3000B (3054B) , possibly processor?

[pcarew]

Hello all,
I have a TDS3054B that used to work, but had not been powered on for 3-4 years.
When I did power  it  on, it wouldn't boot, just white backlight and fan. No other activity.
Here's what I looked at so far:

• Power Supply and regulators - Good

         All looks good. 15V from Power supply. Regulators generating +/- 5V and 3.3V

• Oscillators - Good

         Both 48Mhz and 75Mhz oscillators working

• MAX708 Reset - Good

         Generates reset at power on as expected

• MPC8660 Processor running  - Bad

There seems to be no life whatsoever on the main board from the processor. I've checked address lines in various places/chip pins and there is *no* activity

I'm suspecting either a dead MPC860 or maybe it needs re-balling.

Have others encountered this on a TDS scope before?
Before I start taking any drastic action with this board, does anyone have any other suggestions as to what to check?

Thanks
Paul.

[StefanF]

I had also a blank screen with my 3014B.
There was still activity (Delay led turned on when pushing delay button,also react on autoset button.)
The culprit was the display itself.
I could manage to get the scope(display) running by powerwing the scope up for 30min, then turn it off and directly turn on again.

Stefan

[sicco]

I made a BDM (PowerPC legacy background debugging port) adapter, and wrote pc code for a ftdi ft2232 usb adapter that uses this backdoor. On a good scope this allows you to peek and poke into the mc860, and beyond.
BDM port is on ~5 pins of the 100 pin expansion connector.
I think BDM works even when there’s no cpu clock.

Published elsewhere in eevblog. https://www.eevblog.com/forum/repair/tds3014-adventures-(seeking-75-75mhz-oscillator)/msg3704437/#msg3704437

There’s an extra serial maintenance port also on the 100pin connector, TTL level, that spits out how VxWorks is booting. Maybe that port still tells you something.

You may want to check a clock buffer chip, a SOT23 ic not too far away from the mc860.

[pcarew]

Thank you Sicco, this is helpful.

[pcarew]

I'm continuing to examine the TDS3054B motherboard and looking to identify the various ICs surrounding the MPC860.

Does anyone know what this 5 pin device is (circled in red in attached JPG)?
( The photo is taken from Dave's teardown video as I'm not in front of my one at the moment)

It's marked as 7Z2G but I'm failing (or google is failing) to find/id this device.


Thanks

[rg58]

Could this be 7Z26, maybe?

https://www.onsemi.com/pdf/datasheet/nc7sz126-d.pdf

[pcarew]

Thanks 'rg58', you may well be correct. It looked like a 'G' to me, but that could well be a '6'

[sicco]

That’s that sot23 buffer. And it’s something as in that Onsemi pdf.
I think input was 25 MHz, coming out of the very big big NS chip, and is the 75 MHz oscillator divided by 3.
And output is CLK in to the XPC860. The XPC860 PLL’s that up to more for its system clock.

[pcarew]

Hello Sicco, that's great info. Thank you. It'll be next on my list to check out when I'm back home.

[pcarew]

Hello Sicco,
I hope your 2023 is off to a good start.

I've finally had a chance to take a closer look at the "7Z26" buffer chip.
I believe you're correct, that it has a 25Mhz input on pin 2 ( I can see that on my scope), but no output on pin4. Looking closer, the OE on pin 1 is set Low, IE the pin4 output is tri-stated.

Do you have any insight as to what should be driving the OE pin (pin1). This board is pretty dense and so it's hard to see where this signal is coming from.

Thanks
Paul.

[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.

[Mrnt]

Did you make any further progress on this? Curious as to whether the processor needed reballing.

[pcarew]

Hello,
Many apologies for the exceedingly slow response.

To cut a long story short, it's still an ongoing project. I have a new processor and I need to get the old one removed and the new one in it's place.
However, that is all easier said than done due to the density of the main board. I'm working up my BGA de-soldering skills, but I'm not ready to risk the board yet, but it is my intention to get this done sooner or later.

Best
Paul.

[pcarew]

Well I know it has been a year and a half since I last posted on this thread, but I *finally* got around to removing/replacing the Motorola Processor BGA.
I replaced the chip with a new one purchased from Motorola/NXP

And.....drum roll.... **No Change** :-( :-(

Same symptoms, blank screen with white back light and fan running, no other activity

So after all this time, I think that was a 'red herring'

Hmmmm....