Incorrect reference voltages and hot U5

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TMH01
Posts: 6
Joined: Sat Feb 10, 2018 4:19 pm

Incorrect reference voltages and hot U5

Post by TMH01 »

Hello... I am getting incorrect voltages at the reference points, including small positive values at V- and AV-. Additionally, U5 gets very hot very quickly. SW1 is set to GND. I have resoldered all of the joints on the analog board to be certain they are good. C8, C10, C11 all appear good. Is it correct to assume that this is a faulty voltage regulator at U5?

Input: 9.1V
V+: 8.28V
AV+: 4.94V
V-: 0.46V
AV-: 0.81V
V1: 2.28V
V2: 4.49V
V3: 2.25V
V4: 3.36V
TMH01
Posts: 6
Joined: Sat Feb 10, 2018 4:19 pm

Re: Incorrect reference voltages and hot U5

Post by TMH01 »

The vendor I purchased from (Banggood) replaced my unit. I have assembled the new one and am still having issues. U5 no longer gets extremely hot, so I think that issue is resolved. However, I still see incorrect voltages. At the very least, I now get a negative value on V-, but it's not a correct one:

Input: 9.14V
V+: 8.34V
AV+: 5.03V
V-: -2.20V
AV-: 0.43V
V1: 1.84V
V2: 4.49V
V3: 2.65V
V4: 3.43V

I have checked, re-checked, and re-re-checked every solder point for every component I assembled. I do not have the tools to work with any of the SMD components, so I have no good way to test any of the other pre-soldered parts. I have analog board PN 109-15001-00F.

I'm very frustrated at this point. Please provide any suggestions you might have! Is there anything else I can check? Or are these units such junk that I received two bad ones in a row?
alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Incorrect reference voltages and hot U5

Post by alphaseek »

I assume you have the new "E" analog board. If so, it seems it could be a bad U5 or a bad U6, or something downstream from U6 that's drawing excessive current - a near short. I don't know how you would test those possibilities with everything being SMD. Maybe someone else will have an idea.

One thing I would suggest is to make sure you have C10 and C11 installed with the correct polarity. C11 in particular should have its positive side connected to ground, and its negative side connected to AV-.
TMH01
Posts: 6
Joined: Sat Feb 10, 2018 4:19 pm

Re: Incorrect reference voltages and hot U5

Post by TMH01 »

SOLVED!

It appears my second unit shipped with some bad electrolytic capacitors. I have replaced them with some others I had on hand, and everything is working as expected.

I'm curious if my first unit had the same problem, so I will try the same fix there at some point - though with the heat issue on U5, I suspect that may be a different problem.



Alphaseek: Thanks for the suggestions, though I was able to get this working last night! I actually have the "F" revision. You were on the right track with the C10 and C11. Everything was soldered in correctly, so that's why I was so frustrated! Thankfully, replacing them completely did the trick.
TMH01
Posts: 6
Joined: Sat Feb 10, 2018 4:19 pm

Re: Incorrect reference voltages and hot U5

Post by TMH01 »

I tried new caps in the original unit with the overheating U5. No change. So, I think that one is definitely a faulty voltage regulator.
alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Incorrect reference voltages and hot U5

Post by alphaseek »

TMH01 wrote:I tried new caps in the original unit with the overheating U5. No change. So, I think that one is definitely a faulty voltage regulator.
Possibly, but a short somewhere downstream could also cause the overheating.
alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Incorrect reference voltages and hot U5

Post by alphaseek »

TMH01 wrote:SOLVED!
Alphaseek: Thanks for the suggestions, though I was able to get this working last night! I actually have the "F" revision. You were on the right track with the C10 and C11. Everything was soldered in correctly, so that's why I was so frustrated! Thankfully, replacing them completely did the trick.
Well now I'm confused. We have documentation for the E versions of both boards, which are supposed to be the latest. But you have an F version of the analog board? What about your main board?

Does anyone have any information about this F board.
TMH01
Posts: 6
Joined: Sat Feb 10, 2018 4:19 pm

Re: Incorrect reference voltages and hot U5

Post by TMH01 »

alphaseek wrote:
TMH01 wrote:I tried new caps in the original unit with the overheating U5. No change. So, I think that one is definitely a faulty voltage regulator.
Possibly, but a short somewhere downstream could also cause the overheating.
Is there a definitive way to determine if there's a short? I wouldn't mind getting the first unit working, too. I already verified that U5 receives the correct voltage on pin 8.
alphaseek wrote:
TMH01 wrote:SOLVED!
Alphaseek: Thanks for the suggestions, though I was able to get this working last night! I actually have the "F" revision. You were on the right track with the C10 and C11. Everything was soldered in correctly, so that's why I was so frustrated! Thankfully, replacing them completely did the trick.
Well now I'm confused. We have documentation for the E versions of both boards, which are supposed to be the latest. But you have an F version of the analog board? What about your main board?

Does anyone have any information about this F board.
The main board is "E1" and the analog board is "F." I purchased from Banggood. Both the original unit and replacement came with the F revision. The first unit shipped 1/27/18 and the replacement shipped 2/19/18.

I didn't check the main board or firmware version of the first unit before packing it away, but the replacement is definitely main board version E1, analog board version F, and firmware version 111.

Everything I see on this forum about the E version seems to also apply to the F version, at least in terms of part numbering (U5, C10-11, etc.), so I suspect they're extremely similar.

Here are a couple pictures of my working unit (with replacement cap at C10).
Analog Board
Analog Board
Main Board
Main Board
alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Incorrect reference voltages and hot U5

Post by alphaseek »

Is there a definitive way to determine if there's a short? I wouldn't mind getting the first unit working, too. I already verified that U5 receives the correct voltage on pin 8.
Well, you now have one working Shell and one non-working Shell, both probably with the same F analog board. So if it were me, with the power off, I would measure the resistance between the various test points in the AV- circuit and ground, looking for differences. The V- and AV- test points, for example, might be interesting places to test for differences between the two boards. But the problem with SMD stuff is that its very hard to desolder stuff to separate the circuit into segments, looking for shorts.
Everything I see on this forum about the E version seems to also apply to the F version, at least in terms of part numbering (U5, C10-11, etc.), so I suspect they're extremely similar.
I wonder if that's really an "F", or just a silkscreen screwup of "E1".
TMH01
Posts: 6
Joined: Sat Feb 10, 2018 4:19 pm

Re: Incorrect reference voltages and hot U5

Post by TMH01 »

alphaseek wrote:
Is there a definitive way to determine if there's a short? I wouldn't mind getting the first unit working, too. I already verified that U5 receives the correct voltage on pin 8.
Well, you now have one working Shell and one non-working Shell, both probably with the same F analog board. So if it were me, with the power off, I would measure the resistance between the various test points in the AV- circuit and ground, looking for differences. The V- and AV- test points, for example, might be interesting places to test for differences between the two boards. But the problem with SMD stuff is that its very hard to desolder stuff to separate the circuit into segments, looking for shorts.
Everything I see on this forum about the E version seems to also apply to the F version, at least in terms of part numbering (U5, C10-11, etc.), so I suspect they're extremely similar.
I wonder if that's really an "F", or just a silkscreen screwup of "E1".
I wondered that, also. But both of my units have the same printing. There are some references to an F revision on the Q&A board at Banggood, too. Unless there is a run of boards with the same silkscreen error, I think it's a real revision (albeit, minor).
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