A1502 820-3476 No S4 - I'm lost

[Tony Tone]

Beer bramaged. Found and fixed the S5 (clap, clap, clap); missing S4. Been in circles for days & days. Need pointing finger.
Have: PPVRTC_G3H & PP3V3_SUS. Think I'm stuck around U1900 & Crystal?

 

[dukefawks]

First double check if 5V_S4 is pulsing or coming high for just a fraction. If there is absolutely nothing at all I would first look around the RTC circuit R1300-1303 and for 32KHZ from U1900 pin 12.

 

[Tony Tone]

Duke. Awesome. Nice to meet you. I only have a piece of shit analog oscilloscope. I was seeing Louis's video on 1/4 spin earlier, LOL. The R1300's and whole region are good (visually) and get 3.3V. I'm getting 2 paralel lines on the oscilloscope and they look like they are moving pretty fast (like the curve of a lowercase f). Think I need a digital one? I can order one right now. & dead on 5V_S4.

& I am going to look into what these areas are about too. Thank you for some direction : )

 

[dukefawks]

Just use a multimeter, even a $5 one will show at least something. Checked for a short on the 5V bus?

 

[aprendiz]

Measure voltage on R1300-R1303 should be about 3.3V on both sides of all resistors, I guess the oscilloscope can read 32Khz from U1900, this is the clock signal for PCH, without it nothing will work....

 

[Tony Tone]

No shorts on 5V's. And 3.3 on all 4 resistors. Thanks for the tidbit on clock on PCH (good place to check 1st , or know about, thank you).
I take that back...
R1301-2 is 3.0
R1302-2 is 3.2

 

[Tony Tone]

No Title

How do I delete this comment? LOL

 

[Tony Tone]

4.8v is at C7524 & 12v Q7520 pin 1. Q7520 good?

 

[Tony Tone]

No V's on 1, 2, 4, 5, 7, 8, 9, 11, 27, 28, 30, 32 on U7501.

 

[Tony Tone]

Test point 209 is 3.0V. That suppose to be 3.3?

 

[Tony Tone]

What if it wasn't 32Khz (for example) & something less or more or not at all would mean U1900, crystal, etc bad?

 

[aprendiz]

It must be 32 Khz, test point 209 is ok, check U1900 maybe something corroded on this area......... where originally was the damage?

 

[Tony Tone]

Wow. You guys are dedicated to assisting. Thank you. & thank you for some direction. I'll order my digital oscilloscope bc it seems important. Thought this analog would be good enough. & I'll look closer to what you guys are pointing at and report back : )
Not trying to have you guys fix it, I gotta do my part too. Don't want to waste your time.
Thank you.

 

[dukefawks]

You don't need a digital scope any 1960 crap scope is good enough to measure RTC. Voltages you do with a multimeter. Fancy tools are not going to magically fix these boards.

 

[Tony Tone]

Yes, there is some corrosion in that area. I used a cap from an iPhone and something else off a 1278 (have lots of 1278's to pull from but thats it, visiting a local recycler for dead Mac boards). But I think this is the problem.

 

[Tony Tone]

My assumptions that I am at least seeing something on the 1960's silly scope is good enough to assume its functioning properly being more practical is a good one.
Thank you. I think the area I did work on around the U1900 is not good enough. I'm going to recheck it. U1845 looks bad around there. I'm waiting on an appointment at local recycler to find a donor board, don't trust whats online bc they look pretty janky. Thanks. I'll follow up with my results.

 

[Tony Tone]

..............

 

[Tony Tone]

How can you tell if the PCH is bad?

 

[Tony Tone]

So I went gorillas and changed every single thing that even looked bad on the entire board. Same thing. The clock signal looks good, it looks like Louis's on his video (analog though).
Good rails: PP5V_S5, PPRTC_G3H, PP3V3_SUS, PP3V3_S5, PP1V05_SUS.
No S4's...

 

[Tony Tone]

I notice R5233 is missing. But it looks like it is originally NO_STUFF. Donor has empty too. But the schematic shows a resister there. Should I put it? Or would that throw it into one of those modes? LOL.