820-2879 green light, not turning on and not charging

ytesfay80

New member
This board was sent in as not turning on. The light on the charger stays green and it doesn't turn on when I hit the power button or when I short the onoff pads.

Here are some measurements I took before replacing the U7200 chip.

CHGR_DCIN 16.35
CHGR_ACIN - 4v
PPBUS_G3h - 12.58
pp3v42_g3h- 3.41v
Resistance Pins 17/18 U7000 - 2.9ohms
Resistance Pins 27/28 U7000 - 20.2ohms
u5010 voltages were all fine.
shorted smc_onoff_l to ground and saw the voltage go to 0v on u5010 but still doesn't turn on
U7200 (Pin 1 - 0v - Pin 6 - 0.78v - Pin 16 - 12.58v)
SMC_PM_G2_EN - 3.4v
----------------------------------------

Q7221 was showing 3.38v on pin 2 and 0v on the drain Pin 6 so I replaced the TPS51125(U7200)
There was still 0v on Pin 1 of U7200 so I replaced Q7221. Still made no difference.

I then checked Pin 16(VIN) of U7200 and noticed it wasn't a stable 12.58v. PPBUS_G3H starts off at 12.58v and quickly goes down to around 5v then jumps back up to 12.58v and repeats. I even took the TPS51125 off of the board and measured and PPBUS_G3H still does the same thing.

What could be causing this?
 

2informaticos

Administrator
Staff member
SMC doesn't get 3V_S5 on time and resets ISL6259 I suppose; duke explained this somewhere...
First of all, check resistance to ground on L6995; 200K resistance scale, not diode mode.
If get less than 30K trash the board; this means bad MCP almost all the time.
If seems to be good, check if VREGx outputs of U7200 are steady.
Also check if any pulse appears at L7220.
If you remove Q7221, both L7220/60 must get voltage; at least pulses.
 

ytesfay80

New member
Resistance to ground on l6995 shows around 2.5Mohms
Pin 8 VREG3 - 0.73v and goes down. I think it shows 0.73 when PPBUS_G3H is 12.58v
Pin 17 VREG5(P5V_S5_LDO) - around .35v and slowly goes down then comes back up

Pin 1 of L7220 is 1.07v when I first plug in charger then goes all the way down to 0.1v then back to 1.07v and repeats.

It sounds like I need to make ppbus_g3h steady before anything else will work.

CHGR_ACOK pulses from 3.27 down to 3.11v. L7030 is 0.477 in diode mode
 
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ytesfay80

New member
ppbus_g3h was a stable 12.58 but there was no voltage on ENTRIP1 before I replaced the tps51125 previously. After I replaced it thats when ppbus_g3h started fluctuating but even when I removed the tps51125 from the board it was still fluctuating.

I have one more of these in my spool and I didn't want to waste the last one if that wasn't the issue.

Should I go ahead and replace it again?
 

2informaticos

Administrator
Staff member
What kind of voltage are you searching at ENTRIP1?
The normal value (enabled) is 0.87V...
I suspect bad solders at new TPS51125; check for short on L7220/60 now.
Put back original chip and post some voltages.
 

ytesfay80

New member
I was always getting 0v on Pin 1 of U7200 and R7271.
With the replacement TPS51125 on the board here is what I got.
L7220 in diode mode - 0.152v
L7260 in diode mode - 0.447v

I put the original TPS51125 on the board and the same thing is happening with PPBUS_G3H and 0v on Pins 1/6 of U7200
L7220 in diode mode - 0.144v
L7260 in diode mode - 0.438v
 

2informaticos

Administrator
Staff member
When PPBUS_G3H is high, VREGx should appear too.
Is better to use o-scope to see if really rise their normal values; at least don't use auto-range multimeter...
If remove Q7221, also should get voltages at L7220/60 at same time PPBUS_G3H is high; if SMC_PM_G2_EN is really high, of course.
 

ytesfay80

New member
I measured as soon as the charger was plugged in with my fluke 115 multimeter and pin 17 of u7200 was 4.24v and it quickly goes down.
Pin 8 was 2.78v and it quickly goes down towards 0.6v then jumps back up to 2.78v and repeats.
SMC_PM_G2_EN is 3.4v.

These measurements are with the original TPS51125
 
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ytesfay80

New member
Okay so I replaced the ISL6259 and now PPbus_g3h is a steady 12.56v.

U7200 was still not getting steady voltage on the VDD Pin so I replaced the TPS51125 with a brand new one and still that didn't solve this.

Now when I checked SMC_PM_G2_EN on R7273 there is 0v there, the resistance is around 95k and in diode mode SMC_PM_G2_EN is 0.45v .
U7840 voltages
Pin 1 - 3.4v Pin 2 - 0v
Pin 3 - 0v Pin 4 - 3.38v
Pin 6 - 0.98v Pins 7/8 - 0v

Pins 8/17 of U7200 are still fluctuating and aren't at the proper voltages.

I'm sure this can be fixed because I fixed this this board for the customer a couple of weeks ago. It was not turning on so I replaced the DCIN board and it was working again. After a week they told me it would no longer turn on.
 

2informaticos

Administrator
Staff member
Don't be so sure...
In the first DC board was fucked some resistor on ADAPTER_SENSE line, which means overvoltage; maybe protection diode.
That could slightly affected SMC, which still worked, but now missing SMC_PM_G2_EN could be result of that.
Check SMC_RESET_L first, if no light on magsafe.
 

ytesfay80

New member
Do you know how SMC_PM_G2_EN could be present before I replaced the ISL6259 but not anymore?
I have a green light on the magsafe.
ADAPTER_SENSE is 3.38v.
SMC_RESET_L is 3.4v
U5010 measurements are fine.

I've tested with 2 know good dc-in boards.

Update: So I removed the TPS51125 from the board and plugged the charger in to see if SMC_PM_G2_EN would come on but it didn't and when I put the chip back on and plugged the charger in the light was dim green and SMC_RESET_L is 0.15v. I don't know what is going on. I've plugged in both DC-in boards and they both are dim green now.

2nd update: I looked around the SMC and found R5260 was corroded and in diode mode 0v to ground on both sides. I removed it and the pads are still 0v to ground in diode mode.
Pin 2 of R5071(PP3V42_G3H) was also 0v to ground in diode mode. Removed R5071 along with U6901 and still shorted to ground.
 
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2informaticos

Administrator
Staff member
"So I removed the TPS51125 from the board and plugged the charger in"
So you may have to trash the board now.
I suppose one high-side MOSFET got burnt...
Never-ever power up a board leaving MOSFETs from a buck converter with the gate floating!!!
 

ytesfay80

New member
Okay I removed L6995 and the short was on Pin 2 side so I injected voltage there and the current was showing around 1 amps then it just started showing 0 amps and the short was gone. I put L6995 back on along with U6901 and now the green light is back.
PPBUS_G3H is showing 12.58v then it will just go to 4v and quickly down to 3v then back to 12.58v for a couple seconds then repeats.
SMC_PM_G2_EN is back at 3.4v.
C7273(PP5V_S5_LDO) pulses from 4.7v and goes down.
C7270(5V3V3S5_REG3) pulses from 3.33v and goes down as well.
I need to get PPBUS_G3H stable as I did before. I'm not sure if these ISL6259s that I am getting from my spool are bad because I've replaced a few different ones and sometimes I get different voltages on PPBUS.

Also, R5260 is still showing 0v to ground in diode mode on both sides.
 

ytesfay80

New member
I replaced the ISL6259 from a donor board and it is still fluctuating as I said previously. I also put flux and heated the SMC to rid of any corrosion under it and that still didn't solve this. Pins 17/18 27/28 resistance and traces are fine.
Any other ideas dukefawks 2informaticos ? I may have to refund the customer and send this back.
 
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2informaticos

Administrator
Staff member
Check resistance to ground at L6995, in 200k scale.
Remove Q7221 and tell us voltages at L7220/60 when PPBUS_G3H is high.
 

ytesfay80

New member
Red probe on Pin 1 of L6995 black on ground in resistance mode 200k scale shows 280kohms.
I removed Q7221 and measured.
L7220 was showing nothing but pulses of 0.05-0.13v.
L7260 was showing no voltage at all.

L7220 in diode mode was 0v to ground on both sides.
L7260 was 0.43v to ground on both sides.

Also now I am seeing 3.38v on Pin of R7273 where before I was getting 0v on it.

Should I remove L7220 and see which side the short is on?
 
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2informaticos

Administrator
Staff member
I'm wondering how can you read 280 value in a 200 scale...
You've probably used auto-range, not 200K selected.

Lift one pin of L7220 and look where the short is.
Be aware, this will not completely discard TPS!
Inject voltage starting with 1V, maybe less; keep the current under the limit of your lab supply.

The short appeared when you powered up the board without TPS; don't do that again...
 

ytesfay80

New member
I removed L7220. Pin 1 was showing 0.002v and Pin 2 was showing 0.07v in diode mode so I went to resistance mode to ground and Pin 2 was OL and Pin 1 was like 5ohms so I injected 1v into Pin 1 and couldn't feel anything getting warm so I went slowly up towards 2v(shows 2amps going through) and the only thing I feel getting warm is U1400 and the opposite side of the board where u1400 is. I put alcohol on those areas and nothing burned away unusually fast.
 
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