Reflow Audio Ic and CPU problem

Question

iPhone 7

Lanzado en Septiembre 16, 2016. Modelos 1660, 1778. Disponible en GSM o CDMA / 32, 128, o 256 GB / Oro Rosa, Oro, Plata, Negro Mate y Negro Brillante.

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modesto @modesto93

Rep: 11

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Publicado: 15 de may. de 2020

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Reflow Audio Ic and CPU problem

Hi friends, I wanted an opinion, unfortunately iPhone 7 with audio chip problem there are really too many around, although I have a good success rate with a Reflow this time it went wrong. The phone does not turn on, I have an absorption of 0.4A from the cable but nothing appears on the display. Disassembled I noticed that the lines "PP_Soc_Var" "PP_CPU_Var" and "PP_GPU_Var" are all in short. So I think the processor is the problem ... I had used a high temperature tape to cover the rest of the logic board leaving only the Audio chip uncovered, with a temperature of 310C. I'm really baffled, I didn't think it could go so bad ...

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Peter N @petern78530

Rep: 295

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Publicado: 15 de may. de 2020

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Do any of the capacitors seem dark or burnt up on these lines?

PP_SOC_VAR, PP_CPU_VAR & PP_GPU_VAR have very low resistance, most multimeters will beep on both sides because of this. So you may not have short.

There is a still possibility heat has gotten through to the other side of the board and caused a short under the CPU or baseband CPU.

I would never reflow an audio IC on the iPhone 7. The problem normally is a broken trace between I2S_AP_TO_CODEC_MCLK and pad C12 on the audio IC (usually caused by a drop or a bend). Reflowing the IC normally wouldn’t reconnect this trace. I always remove the audio IC and repair the trace at pad C12 (also check F12, H12 & J12). Then reball, then resolder the IC. Repairing this trace provides more strength and would stop the problem for occurring again (in most cases).

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Many times it has happened, I wait for the chip to barely move with the help of the flux and most of the time it is successful, then someone happened that had problems with the modem, but I understood that the error was lingering for too long time on the same point with the hot air. I also checked if there were tin balls that could indicate overheating but nothing, 3 short lines and nothing other than the CPU seems to be the culprit. I really don't know how to solve it, most of all the mistake was having taken the success of the operation for granted and discovering that there was no backup of the data inside the phone. In this case if I can find a person who is capable of a cpu reball I will send it ... I don't think there are other good solutions.

15 de may. de 2020 - de modesto

I forgot, in ohms I have an average of 0.15 on the lines

15 de may. de 2020 - de modesto

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Many times it has happened, I wait for the chip to barely move with the help of the flux and most of the time it is successful, then someone happened that had problems with the modem, but I understood that the error was lingering for too long time on the same point with the hot air. I also checked if there were tin balls that could indicate overheating but nothing, 3 short lines and nothing other than the CPU seems to be the culprit. I really don't know how to solve it, most of all the mistake was having taken the success of the operation for granted and discovering that there was no backup of the data inside the phone. In this case if I can find a person who is capable of a cpu reball I will send it ... I don't think there are other good solutions. — modesto

Chris Stables @imicrosoldering Rep: 50.7mil 8 14 101 · Answer 1 · 2020-05-16T00:02:39-07:00

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Chris Stables @imicrosoldering

Rep: 50.7mil

8

14

101

Publicado: 16 de may. de 2020

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"PP_Soc_Var", "PP_CPU_Var" and "PP_GPU_Var" are not shorted they are supposed to have a low resistance. After any audio IC work on the iPhone 7 a 0.4A draw will most likely be a VDD_BOOST line short. Check these caps first for bridging if you cannot see any bridging you will probably need to remove the audio IC. Pay attention to the cap circled.