Announcement

**Stephen** · 04-09-2021, 07:52 AM

Re: A1706 820-00923 Boot looping

Disconnect the webcam. I know it sounds stupid but trust me, disconnect it and see if it updates. Very common issue I seen when the webcam has failed.

Next if the webcam has not failed and it still pops this up, it is more than likely the touchbar, is the touchbar on when you turn it on? The esc key should show up when you boot into recovery etc.

**Stephen** · 04-09-2021, 07:55 AM

Re: A1706 820-00923 Boot looping

Also I am certain you know but the webcam is on the left side of the LCD when trying to remove the LCD. THE left connection and the right side is the backlight. Left is when the battery is facing north. Usually this is how you remove the LCD anyways. DO NOT remove the LCD, just disconnect the WEBCAM and then turn it on and it should post with the update in most cases. If it does post and you just got apple to replace this LCD i would suggest you take it back to APPLE and see you gave me a faulty webcam FIX IT!

**Stephen** · 04-09-2021, 07:57 AM

Re: A1706 820-00923 Boot looping

ALSO, if you confirm it is the webcam then you have to leave it disconnected or the process will loop again. Confirm what you find.

**mon2** · 04-09-2021, 09:32 AM

Re: A1706 820-00923 Boot looping

Thank you for your reply and suggestions.

Could you please confirm which exact cable is the webcam cable?

Is it the one with the ARROW in the shared pic ?

Update - corrected the location of the camera cable - found this detail on youtube.

Is this the correct cable? Silkscreen references the text camera on the PCB.

Also, the TOUCHBAR does NOT show an ESC nor lights up. We are suspecting a corrupt boot internal SSD and attempting to load from an external OS. Will report back in a few minutes on if the boot cycle is correct with the webcam cable removed.

Attached Files

**Stephen** · 04-09-2021, 12:17 PM

Re: A1706 820-00923 Boot looping

Yes the Webcam is that one on the left.

**Stephen** · 04-09-2021, 12:19 PM

Re: A1706 820-00923 Boot looping

The SSD is not corrupt from this model I can reassure you on that. I have experienced this issue before multiple times.

It has always fallen down on the Webcam or the Touchbar needing to be replaced.

**Stephen** · 04-09-2021, 12:25 PM

Re: A1706 820-00923 Boot looping

Also, usually when the webcam is connected the Touchbar will not function as well (if the webcam has failed). Disconnecting the webcam IF it is the webcam would bring back the Touchbar to function properly. If disconnecting the webcam and the touchbar is still not working and you still get this process, I would suggest replacing the touchbar. You can find OEM touchbars (new) on eBay for around 50.00. If you rather not do all the labor for the touchbar replacement then the better option is to get a used topcase known working etc. Again thats from my experience repairing these models.

**mon2** · 04-09-2021, 01:29 PM

Re: A1706 820-00923 Boot looping

Thanks. Removed the webcam cable and the logic board is still boot looping.

The Apple logo tears for a second before shifting to the next screen. As the fans are OFF at this part of the boot process on this system, believe that heat is a factor. Not much after the language selection, the mouse pointer does appear from the OS that is external (mechanical HD over USB) and then reboots.

The touchbar remains dark at all times.

Perhaps time to replace the touchbar?

Can the touchbar be removed off the logic board without removing the logic board? Only to temp test that the touch bar is strapping the system.

Concerned that the 3 phase power supply remains OFF during these events. Perhaps the power rails are not used till later in the boot cycle? (ie. GPU rails?)

**Stephen** · 04-09-2021, 07:57 PM

Re: A1706 820-00923 Boot looping

The touchbar is connected to the logic board but it can be disconnnected. I recommened covering up the keys with Gafton Tape (heat resistant tape) You have to get a heat gun and heat up the Touchbar to remove it. The touchbar is taped down very well. It is a fairly easy process if you protect the keys and remove the LCD (removing the LCD so the heat doesn't transfer over) . You also will need alcohol etc to get it removed to loosen up the touchbar tape. There is no point in worrying about breaking the Touchbar since it doesn't work. Just remember to remove the logic board out and LCD. once you are there you can remove the touchbar. But sometimes we just say screw it and get a new topcase with a working touchbar. Yeah you will save money doing the Touchbar removal and replacing it but at what cost if you never done it before?

**Stephen** · 04-09-2021, 08:01 PM

Re: A1706 820-00923 Boot looping

Also another thing to keep in mind is if you have a spare touchbar topcase laying around with a good Touchbar (maybe bad keyboard) i would suggest swapping it out and see if the Touchbar turns on. It is always wise to test with other parts before assuming it is the problem. We do process of elimination before hand.

Our phases are:
Boot loop issue?
1. Disconnect webcam If success ignore 2. if no success move on to phase 2
2. Webcam is not the problem, remove logic board and plug logic board into another working topcase with known working touchbar. If working ignore step 3.
3. If top case that is known working is still an issue, then LOGIC board is the issue.

A little of future advise:

Keep parts from bad computers. It is good to document which ones work on a computer so you can reuses it.

IE: Bad LCD (broken cracked) but has a known working webcam, so use that plug in external monitor to test webcam is functional.
Good LCD, Bad webcam to make sure the LCD turns on for testing purposes on a LOGIC board
Bad Keyboard, Good Touchbar (keyboard double taps) for testing Touchbar issues.
Good batteries in top cases to see if battery issue goes away with a known used working battery.

etc etc. We always keep spares laying around to isolate issues before we jump into a logic board.

**iMuhtaseb** · 04-10-2021, 06:17 AM

Re: A1706 820-00923 Boot looping

Hello,

First I wish you best of luck with this @mon2.

Second I would like to thank @Stephen about the webcam cable, this might help me w/ my current case.

I'm no professional and I'm here to just give my insight on a similar case faced me when corrosion was near the U4200 chip which apparently is like a daughter chip for the T1 and it prevented the computer from updating. I have no idea if this will help you or not and you can discard my message if you feel it didn't help.

All the best!

**piernov** · 04-10-2021, 07:28 AM

Re: A1706 820-00923 Boot looping

TouchBar won't work if T1 cannot boot. Critical Update Required appears when T1 cannot boot. bridgeOS for T1 is stored on the internal SSD. It requires macOS to be installed on the internal SSD.

https://logi.wiki/index.php/Critical...roubleshooting

**mon2** · 04-21-2021, 02:54 PM

Re: A1706 820-00923 Boot looping

hi. back to this logic board.

1) appears that the logic board only likes to boot the Apple logo if the battery is used. Still stuck on the first issue and the fans are not working. However, not convinced the OS is stable but found another issue...

2) with the battery off, the logic board does not boot at all.

3) with the battery OFF, the external type C power supply shows 5V @ 0.043A and power cycles - never able to negotiate to 20V.

4) Now the investigation is on the power rails that power the CD3215 controllers and the Type C interface connectors.

PP3V3_G3H = 3.41 V
Resistance @ L6900 (PP3V3_G3H) Pin 2 = 9k - 0.3Mohm (no shorted caps) - matches another working A1706 logic board

At this time, know that each ACE (CD3215) controller is showing the same symptoms of power cycling with 5v in via USB Type C -> reaches about 43mA and powers down and repeats. The Type C meter blanks out after 43mA due to the shutdown cycling.

Next, we should confirm the internal LDO rails supplied by each ACE controller is operational?

Is there a 'shortcut' to determine which ACE controller (if any) of the 4 is defective?

Before digging too deep, considering to place a bus analyzer onto the I2C lines to check on if one or more of the ACE controllers are not replying back to the I2C address that is being selected. Then replace that single ACE controller.

Ideas?

**mon2** · 04-21-2021, 05:57 PM

Re: A1706 820-00923 Boot looping

Using fresh type c connector boards, each ACE controller is working to negotiate 20V. More details to follow...

**mon2** · 04-22-2021, 10:47 AM

Re: A1706 820-00923 Boot looping

Hi. Updates and more questions:

1) using the same logic board with fresh USB type C (dual port) cable PCB - the logic board negotiates @ 20V on all 4 Type C ports. This is great news.

2) Next, we took this A1706 logic board and docked inside a completely different chassis (different LCD panel; different battery; different keyboard / touchbar and trackpad). The logic board boots and lights up the touchbar on this different enclosure. Good news again. Still crashing with the same end error message and while we did see the fan spin during a boot off Catalina, we do not see the fan spin during the High Sierra boot process. Respectively, during the HS boot cycle, with the fan not spinning, the CPU heats up and recycles.

I think we are getting closer as the Touchbar is lit up.

At what point should the A1706 be reflashed using the Type C to Type C cable? What is the procedure? Have not used this tool yet. Is it suitable for this issue? We can run the procedure on any macbook with the type C connector?

Attached is the screen from the Catalina boot cycle.

Would someone please confirm if the A1706 should have fan spin during first time boot up? Believe that it should to remain cool.

Thanks.

Attached Files

**mon2** · 07-30-2021, 11:30 AM

Re: A1706 820-00923 Boot looping

Hi. Back to this logic board with the same issues. See the critical update is required boot loop. Using an external boot drive, we can get to the log in screen -> upon using our pswd, the desktop is presenting this error message and reboots.

The touchbar does not light up. We have recently brought in a factory new touchbar but have not yet attached to this logic board. The webcam cable was removed but does not appear to make a difference.

Any suggestions on how to proceed ?

What is the procedure / tools are required to reflash the bridgeOS for T1 ?

Update:

Just found this:
https://www.reddit.com/r/MacOS/comme...os_on_t1_chip/

Any comments on this procedure?

Also, should every coil feature a voltage during the logic board normal boot? Numerous coils are without power which is odd but yet we do see the screen booting / logic board presents a "?" so we are forcing an external boot media. From last time checking, believe that we had wiped out the onboard SSD in an attempt to fix the critical update error code.

**mon2** · 07-30-2021, 12:18 PM

Re: A1706 820-00923 Boot looping

We are following the suggestion by @Piernov to re-load the bridgeOS as per the post on reddit. The OS being used is High Sierra. The unit appears to be stable but has been stuck @ 2 mins left for the last 20+ mins.

Should this loading take this long ? This is a first time experience on the bridgeOS process. Glad to see that the logic board fans are now spinning. The board is also connected to the internet so perhaps downloading this missing link. Will be nice to see the touchbar light up...more details to follow once this procedure is complete.

**mon2** · 07-30-2021, 03:14 PM

Re: A1706 820-00923 Boot looping

Can someone please measure the PPVCCGT_S0_CPU rail upon power up on the A1706 logic board 820-00923 ?

Do you see any voltage upon power up ? We see 0V on all 3 phases @ PPVCCGT_S0_CPU.

Never mind..see the answer here:

https://boards.rossmanngroup.com/thr...booting.58607/

PPVCCGT_S0_CPU will only appear under graphics load; like playing YouTube videos.

The touchbar is from another A1706 and so is the display but facing the same quirky "critical update" message as what the client has reported that started during a bunged up update he was applying. Believe the bridgeOS is now valid since the touchbar lights up and works for the volume / screen intensity, etc. but after inputting the log in password, will reboot.

Really really hate this logic board.

**mon2** · 07-30-2021, 04:01 PM

Re: A1706 820-00923 Boot looping

PPVCC_S0_CPU is fluctuating like mad during and use of the logic board. Observing voltage readings on this Rigol multimeter from < 0.5V to higher but not steady.

During the initial boot cycle, this rail is solid @ 0v8.

Is it normal for the PPVCC_S0_CPU to fluctuate? We see the Apple logo while this rail is moving -> can reach the desktop with touchbar ON but does not last long before the error message and the reboot loop continues.

PPBUS_HS_CPU = 13v0 (steady) into U7210.

If this dualphase power rail is working properly, then we should see a steady voltage rail. Welcome feedback.

Update:

From

https://logi.wiki/index.php/Power_Rail_List

The voltage rail should be @ 1V5 for a similar logic board - 820-00239 but we have the 820-00923.

Also, ran diagnostics and facing an error code PPM002 = RAM problem ? Soldered BGA devices = lots of fun to look forward to. Will review it on Monday. Suspecting the voltage rail for the CPU to be more of a factor raising this PPM002 error code.

Announcement

A1706 820-00923 Boot looping

A1706 820-00923 Boot looping

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment