820-3437 liquid on u7501 and u1900

ielectron

Member
i replaced u7501 (new chip)and u1900 (from donor board), there is green light, i can do SMC reset
-the board takes 0.380A when i connect the charger, than that goes back to 0.200A and stays there

i see no water else where, only on those 2 chips, and some resistors around, i replaced all of them, no here is the measurement for

u7501
10
20
31.245
40
50
61.998
70
80
90
101.998
110
123.4
131.998
145
151.96
161.01
173.3
183.3
191.99
203.3
213.4
223.3
238.57
244.01
253.3
268.33
271.1
280
295
304.8
310
320



u1900
10.135
23.27
30
40.004
53.28
61.19
71.19
80.34
90
100
110
120.125
133.4
143.29
150
160
 

ielectron

Member
in the meantime i found another good board, the measurement for this
u7501
15.5
25.1
31.25
43.33
50
61.996
70
80
90
101.996
110
123.4
131.996
145
151.97
161
173.3
183.3
191.996
203.3
213.4
223.3
238.59
243.59
253.34
268.44
270.38
280
295
300.38
3110.17
325.1



u1900
13.3
23.3
31.2
41.09
53.33
61.19
70
80.56
90
100
110
120.391
133.4
143.3
151.66
160
 

ielectron

Member
so my u1900 is not giving 3.3V on the leg 1, so the crystals are not working? the leg 1 was corroded, i removed it, pad cleaned, chip replaced, but still no 3.3
 

2informaticos

Administrator
Staff member
Did you check resistance to grounat pin 1/U1900?
If OK, then check for 3V at pins 2 & 13 of U1900.

25MHz will not appear untill board starts.
You must get first 32KHz at pin 12.
 

JohnB8812

New member
If you have a short on pin 1, you need to remove U1900 first to see if it goes away. If not, the cap next to it can cause the short. If not that, there are 4 other big caps on the board for RTC. If you remove all 5 caps and U1900 and it’s still 1 ohm, then yes dead CPU
 
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