KC Micro Tronix
Member
Today I fixed a board that had corrosion under U1900 which operates the 25Mhz crystal. I was like wow. Look on the scope. The crystal comes and goes.
Pulled U1900 repealed and replaced and Bam! I got fan spin. so.... I dive into the toybox! I knew there were tons of PM_SLP_S4_L boards in there!
Toy Box first one I grab! 820-00165 missing (PM_SLP_S4_L) does the exact same thing! SYSCLK_CLK25M is erratic. Pops in for a split second. Just long enough for my Tek 784 to trigger lock and and let me see. Then it is gone. Each time it does this I see the current bounce a few mA. Like it was just about to wake up. I changed U1900 and Y1905 (careful not to overtemp) and no change.
U1900 pin 1 (PPVRTC_G3H) 3.3v
U1900 pin 13 (PP3V42_G3H) 3.42v
U1900 pin 5 (PP3V3_S5RS3RS0_SYSCLKGEN) 3.3v
U1900 pin 2,3 (SYSCLK_CLK25M_X2 and X1) intermittent 25Mhz signal
I am thinking that because all these parts come from donors I could easily be throwing bad parts on the board but I have tried twice now. Stop me before I rape a working board! These crystal circuits are not magic. There is not much to them. GIve U1900 power and PP3V3_S5RS3RS0_SYSCLKGEN and Y1905 should sing like a canary. Hopefully I am wrong here and am missing something.
My Toy Box is boards I could not quickly resolve. eBay has been a great way to learn!
Pulled U1900 repealed and replaced and Bam! I got fan spin. so.... I dive into the toybox! I knew there were tons of PM_SLP_S4_L boards in there!
Toy Box first one I grab! 820-00165 missing (PM_SLP_S4_L) does the exact same thing! SYSCLK_CLK25M is erratic. Pops in for a split second. Just long enough for my Tek 784 to trigger lock and and let me see. Then it is gone. Each time it does this I see the current bounce a few mA. Like it was just about to wake up. I changed U1900 and Y1905 (careful not to overtemp) and no change.
U1900 pin 1 (PPVRTC_G3H) 3.3v
U1900 pin 13 (PP3V42_G3H) 3.42v
U1900 pin 5 (PP3V3_S5RS3RS0_SYSCLKGEN) 3.3v
U1900 pin 2,3 (SYSCLK_CLK25M_X2 and X1) intermittent 25Mhz signal
I am thinking that because all these parts come from donors I could easily be throwing bad parts on the board but I have tried twice now. Stop me before I rape a working board! These crystal circuits are not magic. There is not much to them. GIve U1900 power and PP3V3_S5RS3RS0_SYSCLKGEN and Y1905 should sing like a canary. Hopefully I am wrong here and am missing something.
My Toy Box is boards I could not quickly resolve. eBay has been a great way to learn!
Attachments
Last edited:
