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820-3330 intermitting startup and orange light - fan twitch if dead

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Fizzl92

Member
This 820-3330 can work perfektly fine. Unfortunately only randomly it starts and works. The rest of the time its dead with just an green light (orange light is just there it it decides to start) and fan twitch ~ every 1 second. I can hear a clicking noise (i guess from a transistor?!) if the fans twitch.
I checked a few things and as sometimes even the green light was fading away i replaced ISL and SMC already. Now the green light is there every time (orange light still only if it starts) but still starts only randomly...
I checked all rails for shorts and PP1V05_TBT has just 17 Ohms to GND (not sure if thats ok?). If it starts there is 1,1V on that line...
So i am confused at this point.
 
2informaticos

2informaticos

Administrator
Staff member
You can remove U3815, if you have any doubt with PP1V05_TBT rail.
I don't know which value should get there.
17 ohms could be normal, beeing Thunderbolt core power rail.

You must post some voltages, signals level when board doesn't start...
 
2informaticos

2informaticos

Administrator
Staff member
if I correctly understand, machine gives sometime problems on charger only.
You must post some voltages in that moment.
 
2informaticos

2informaticos

Administrator
Staff member
OK, so you have charger related issue.
First of all try known good working 85W charger.
You can also try bench power supply, with the cable removed from 85W charger.
Change Q7080, just in case.

Do you get steady high CHGR_ACOK signal?
 
F

Fizzl92

Member
Changed Q7080 - no change. I tryed defferent, known good chargers ( 1x 85W that works with other devices and 1x 60W with customer battery on Bench power supply)
With the same chargers it works a moment later randomly...
If i plug in a battery everything is fine and it works instantly. Unplug battery and its dead again!?
CHGR_ACIN = pulsing 3.8 V - 3.9 V
CHGR_ACOK =also pulsing 2.2 V - 2.3 V
 
Last edited:
F

Fizzl92

Member
Unfortunately the next time i have access to a scope is on monday. I removed C7011 and now it works with charger too. But i had this situation already a few times and later the same day the problem returms. Maybe its a heat related problem?
I'll report back if it dies again and post scope readings on mondey if problem returns.
Thank you.
 
F

Fizzl92

Member
As far as i can tell they drop down all the way to 0V. But it seems like my CRT is having some problems as it istn?t showing 0V if i do not measure anything. Its lower than the screen can show without me measuring something no matter what i do... So i am not sure if they acrually reach 0.0V.
 
F

Fizzl92

Member
I got another scope and accurate readings now. I measured CHGR_ACIN and CHGR_ACOK. As it is still a CRT i attached the waveforms as a handpainted picture.
Would be really great if you could help me with this.
Thank you.
 

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2informaticos

2informaticos

Administrator
Staff member
PPDCIN_S5_CHGR still pulsing when F7040/41 removed?
Did you try another charger?
Try also bench power supply with 85W cable.
 
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Fizzl92

Member
No, my bad. PPDCIN_S5_CHGR is only pulsing if fuses are attached. Like every other rail is only pulsing if fuses are attached. Yes, i did try 4 chargers already. Totay i got another 85W original sealed one and same thing. Unfortunately i only have a 60W at bench supply and dont want to cut off one of my original chargers if there is any other way...
 
2informaticos

2informaticos

Administrator
Staff member
This board will not start with 60W charger alone, without battery.
But I doubt you've got 4 bad chargers...
Check if board works in SMC bypass mode, on charger only.
 
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