A1707 / 820-00928-A Won't boot

BillyE

Member
I don't have a thermal camera, it would be nice, but I think U3200 is getting hot while checking out UB300 & UB400
 

2informaticos

Administrator
Staff member
1.1 LDO only appears on the powered port.

All USB-C channels must have same behavior.
Seems that you have problems on U3100/200 area.
Compare diode mode readings on LDOs of all CD3215 chips.
 

BillyE

Member
ok, I'm back working on this thing, If I do a diode check on C3208:1 and C3205:1 they both read as ground. I guess I need to pull them out and verify they are bad out of the circuit? But I assume it's a pretty safe bet they are both fried? Should I assume the CD3125 is bad as well?
 

2informaticos

Administrator
Staff member
When you have two shorted rails, the most probably culprit is the common component; U3200 in this case.
Do you really think to have 2 caps shorted (not even connected in the same rail)?
 

BillyE

Member
That makes sense that it's most likely the CD3125 that's bad. I do have a new one I could try and replace it. It will be my first one to replace with a hot air gun. I guess everyone has to have their first. I guess remove it and then check the caps again to verify?
 

BillyE

Member
ok, got the chip off, and pad cleaned up. But I lost resistor R3095 and capacitor C3205 doesn't show short, but it appears to be open.
So I need to order those before I can continue. Any suggestions on best place to buy those? Digikey, Mouser I guess?
 

2informaticos

Administrator
Staff member
Search an workshop on your area.
You may have luck to find someone that can sell you a scrap board; or required components only.
 

BillyE

Member
ok, good news my parts came in, bad news I'm missing some so I still can't finish. But I have a stupid question.
C3205 showed open so I assumed I needed to replace it. So I did. But it still shows open or OL on diode test. I can see ground on pin 2 of C3205 and I can see continuity between pin 1 on C3205 and Pin 2 on U3200 would be. I can read the capacitance across C3205 and it's spec'ed a 1uf cap and I'm getting like .96 uf so the cap seems ok. It's a ceramic cap so polarity shouldn't be an issue. Why would I still get OL on diode check on pin 1 of C3205?
 

2informaticos

Administrator
Staff member
Is a capacitor, what do you expect to show in diode mode?
Try to achieve basic electronics knowledges...
 

BillyE

Member
All the other capacitors show a value in diode mode but this one? Shouldn't it show a voltage drop across the capacitor?
I did find the other resistor I needed so I can attempt to put the U3200 back on. My SMD skills are terrible so I have little hope but gonna try anyway, it's the only way to learn. But the capacitor showing OL bothers me. I hate to be stupid but what am I missing?
 

2informaticos

Administrator
Staff member
ALL CD3215 MUST be soldered on the board; and in good working condition.

Do not compare diode mode reading for a lonely capacitor with the one soldered on the board.
Even onboard, C3205 remains alone once U3200 is removed.
When you check onboard components in diode mode, the reading is affected by ANY other component connected in same point.

So difficult to learn something about capacitors with Google?
 

BillyE

Member
ok, I give up, I'm sure a pro could repair it, but it's not worth the effort. I tried to put a new CD3125 on and it didn't sit right, and while trying to remove it and clean the pads I got to aggressive trying to remove the solder from the pads and damaged a couple of pads. I tried bending some fine pieces of wire to make a new pad, but I don't have the dexterity and even if I did trying to get the "new" pads epoxied down level with the factory pads would be a nightmare. Oh well I learned a lot. Far from ready to fix much, but it's a start. I need a lot more practice using a SMD rework station! This is just such small stuff to work with it's gonna take practice. I appreciate the help but it's just over my head at this point.
 
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