Clock reading not as expected

[ijor]

MMU P5 reads 2 MHz while 16 MHz is expected.
...
I could measure no direct continuity between MMU P5 and Shifter P39, but neither could I in a working ST.

2 MHz on MMU clock input would be almost impossible. You are likely measuring the wrong pin.

[rubber_jonnie]

That's an inductor not a capacitor, though I'm not sure why it is there, but looks like probably a factory bodge. It looks normal, see the picture of another board here: ST Mainboard

At least 2 mainboards in this section of the forum have the same bodge as yours. Later revisions may not have it, or have it integrated into the PCB.

Thanks, I've corrected my post.

You can do continuity tests without worrying about damage. You need to go point to point and see if there is anything odd going on.

When I look at the schematics, I see P39 go into an arrow shape saying 16MHz, but no traces after that. I see the same kind of arrow shape saying 16 MHz near MMU P5, connecting to it. But I can't see how it routes in between, what components it passes. How do I find that?

I could measure no direct continuity between MMU P5 and Shifter P39, but neither could I in a working ST.

Yes, that's unfortunately the way the schematic goes, and quite normal. You'll need to get a magnifying glass and manually track the traces on the board.

[satjanand]

MMU P5 reads 2 MHz while 16 MHz is expected.
...
I could measure no direct continuity between MMU P5 and Shifter P39, but neither could I in a working ST.

2 MHz on MMU clock input would be almost impossible. You are likely measuring the wrong pin.

Well, this is the pin I'm measuring.

IMG_20230222_184510_edit_40200617832927.jpg (297.05 KiB) Viewed 1429 times

[satjanand]

Yes, that's unfortunately the way the schematic goes, and quite normal. You'll need to get a magnifying glass and manually track the traces on the board.

Oh really? That simple? Let's get some magnifying glasses then!

[rubber_jonnie]

2 MHz on MMU clock input would be almost impossible. You are likely measuring the wrong pin.

Well, this is the pin I'm measuring.

IMG_20230222_184510_edit_40200617832927.jpg

You're on pin 8 there, not 5. Pin 9 and 10 are marked on the PCB, the corner of the IC .

[LarryL]

2 MHz on MMU clock input would be almost impossible. You are likely measuring the wrong pin.

Well, this is the pin I'm measuring.

IMG_20230222_184510_edit_40200617832927.jpg

That is Pin 8 RAS0

[satjanand]

Well, this is the pin I'm measuring.

IMG_20230222_184510_edit_40200617832927.jpg

That is Pin 8 RAS0

Well, this is the pin I'm measuring.

IMG_20230222_184510_edit_40200617832927.jpg

You're on pin 8 there, not 5. Pin 9 and 10 are marked on the PCB, the corner of the IC .

Oh dear. I read it as "6", didn't notice the "10" there.

Thank you very much for clearing that up, that's solved now.

Back to cleaning and adjusting sockets and ICs.

[satjanand]

Would be incomplete without expressing how much of a clown this makes me feel.

But thankful for all the help we can get here.

Will refrain my next posts to the Noob channel

[rubber_jonnie]

Would be incomplete without expressing how much of a clown this makes me feel.

But thankful for all the help we can get here.

Will refrain my next posts to the Noob channel

We all have to learn sometime, I really wouldn't worry about it if you get something from the process.