[SOLVED]820-00165 - No 3.3V on Pin1 of SPI-ROM

[bjf]

Ok, I'll try that. Is the order of things: power --> pgood --> clock --> ROM? I know that's way oversimplified but I'm trying to figure out where the stopping point might be. If R1962 was lower would that have meant no pgood?

 

[bjf]

So does this mean that the ROM chip (or it's circuit) could be responsible for this? It's not something that happens before the ROM chip is accessed? I have no idea of the order of events when it turns on so I'm not sure of the logic.

 

[dukefawks]

If the system cannot access the ROM it will power cycle like it is doing now.

 

[bjf]

Ok, good to know, I thought the fan would cycle on and off even without the ROM functioning.

 

[dukefawks]

Actually the fan would be cycling, but the pulse is so short the fan has no time to start up. Without the ROM all S3 and S0 busses will be pulsing.

 

[bjf]

No Title

Ok, so pin 1 on the SPI ROM is open - no reading in diode mode. ROM is removed. Pin 1 has continuity to U6101. I've replaced U6101. I'm not exactly sure of the orientation of the U6101 chips I just got in the mail. I'm attaching a picture. I'm assuming the bottom right is pin 1. No dot, just a line. Any thoughts?

 

[dukefawks]

Get a scrap board so you can also compare measurements and take the correct chip from the donor. I'm pretty sure pin 1 should have something on diode mode with red to GND. All pins must measure something at least. I have no scrap 00165 to compare here right now to be 100% sure. Just order a pile of scrap boards, you will need them anyway.

 

[bjf]

Yeah, I compared it to a another 00165 and it's supposed to be around .590 with U6101 present and ROM removed. It's open with U6101 and ROM removed. I've used up all of my U6101 chips from donor boards. That chip is only on 2015 Air and Retina boards so they went fast which is why I bought a large quantity of new ones. Just wasn't sure of the orientation but I have it now (opposite of my pic.)

​So, the results: No change after installing newly purchased U6101. And no change after installing known-good ROM and factory U6101 from other 00165 board. It still gets 0V on pin1 of ROM and around 1.1V on SPI_MLB_CS_L / SPI_SMC_CS_L. Also, I've confirmed that SPI_MLB_CS_L / SPI_SMC_CS_L will measure 3.3V on a good board with no ROM or U6101 installed.

 

[dukefawks]

If there is no diode mode measurement on pin 1 then U6101 is not soldered right. Check all pins of U6101 on diode mode with it removed and ROM installed of course. Must be bad trace somewhere.
Also do not swap ROMs between boards you will have ME issues, put back original!

 

[bjf]

Sorry, I left that out of the results above. The measurements on this ROM are normal now (.590 on pin 1) with the known-good U6101 installed correctly. I had the open result because I had U6101 reversed. As far as the ROM swap, it's only for testing. No intention of leaving them that way. To be sure of things, I tested this boards ROM and U6101 on my known-good board and it powers up normally.

So the problem is with SPI_MLB_CS_L / SPI_SMC_CS_L not hitting 3.3V. It's at around 1.1V. It looks SPI_SMC_CS_L comes from the SMC. Diode measurements on that line are at .615 versus .515 on a good board.

 

[dukefawks]

Remove R6117 and check both sides on diode mode.

 

[bjf]

R6117 Diode Measurements

This Board:
Pin 1: .733 - SPI_SMC_CS_L
Pin 2: .614 - SPI_MLB_CS_L

Good Board:
Pin 1: .730 - SPI_SMC_CS_L
Pin 2: .514 - SPI_MLB_CS_L

So this seems hopeful.
To take this a step farther I removed U6101 on both boards.

Good board Pin 1 stays at .514.
Bad board goes open.

I tested the continuity between R6117 and R6120 and U6101 and it's good. Continuity through R6120 and R6125 is good also. Both are measuring 43 ohms. Continuity to R6110 is shot. I think I have the problem.

**I accidentally just hit Submit so this post is a little premature, but I'm about to run a wire. I'll update after the results.

 

[bjf]

Got it, beautiful. This was a good win. 2015 i7 board. Thanks for getting me there.

 

[dukefawks]

No problem, but I already called it in post #4!