Do you get 25MHz at SYSCLK_CLK25M_SB?
O-scope, or frequency meter needed to properly check it.
Change it, if you are not sure...
O-scope, or frequency meter needed to properly check it.
Change it, if you are not sure...
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2012 MB Air 820-3208-A voltage fluctuations
- Thread starter da_muffinman
- Start date
da_muffinman
New member
Well I'm not sure...and I'm also inexperienced so I don't know - does testing or replacing the clock chip sound like a good idea to anyone else? I'm at a loss with this one.
The Fluke multimeter is able to measure frequency. SYSCLK_CLK25M_SB measures 0 Hz
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Change that chip is a 5min job; if you have it, from some scrap board...
PCH will not run without that oscillation.
PCH will not run without that oscillation.
da_muffinman
New member
I replaced the clock chip U2700 and unfortunately there is seemingly no change in voltage anywhere. Any other ideas?
When there exists oscillation, you can read 0.75, or 1.75V DC; I do not exactly remember the value.
However, you can confirm its presence 100% only with o-scope or frequency meter.
To get it, U2700 requires 1.8V at pin11, check that.
However, you can confirm its presence 100% only with o-scope or frequency meter.
To get it, U2700 requires 1.8V at pin11, check that.
Inwerp
New member
no
well, all the fluctuation you see is a sign of boot loop, your main problem. the common techniques are to try good-known BIOS, check for the shorts on all peripheral chips (like audio IC), try to start it in SMC bypass mode, and so on. If you see that board starts till the FAN spin, it is already enough to say that the higher logical level is present, this is not the chime but still it shuts down with the reset signal released by one of the main ICs which would not happen with the dead clock. MM Frequency meter is not something you could use to test clock chip, it is used primarily for mains in sub-Khz range. To check if BIOS is being actually read, you can use a LED (in series with ~100Ohm Resistance, of course!). Just connect it between ground and Data line on your bios chip, it will blink slow enough to see if you're getting any activity.
Your question about current measuring and voltage change on clock chip shows that you might need some more theory. For example, if you're measuring "Current" by putting probes between ground and any point of the circuit, you're simply destroying the board since current measuring works only in series and your multimeter's resistance is close to zero in this mode. If done properly, it does not affect the circuit, if wrong - sure it burns the shit out of your board
da_muffinman
New member
Thanks for your response. I have implemented the LED test, connecting the light and resistor between ground and pin 5 of U6100 (SPI_MLB_MOSI) which I believe according to the data sheet in the data line in. The LED indeed lit up for a second, then turn off for a millisecond then back on for a second, etc. So, this means the bios is being read. I'm sorry this thread has taken so long to develop but I am still at a loss here. Should I test the SPI data line resistors?
da_muffinman
New member
Bumpppppppp
You must check all SPI termination resistors, traces and solders around U6100.
Also try new BIOS.
Also try new BIOS.