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Old 10-26-2021, 10:06 AM   #1
dicky96
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Default Help required identifying G78A IC - Radeon HD 5870

Hi guys I have a Raedon HD 5870 here

It does not power up, in fact it only draws about 100mA from 12V and 3.3V combined..

I can only find 12V and 3.3V on the card, I don't think 5V or anything else is present.

There are three components near the rear of the card marked G78A - can anyone identify these?

They all have 12V on the right hand pin, the centre pin connects to ground, and 0V on the left hand pin. This sounds like they should be fixed output LDOs but it doesn't make sense that all of them are faulty (no output) and it doesn't make sense that the centre pin is short to ground (rather than should be ground) as the graphics card draws almost no power.

Also I have another chip in this area which is a buck controller - the buck coil has no voltage and I can't find a connection from 12V to the controller chip so don't know where it gets it's input power. I also could not find a datasheet - can anyone identify this? V2AF 837

There are also two more ICs in this area, I identified as uP7701U8 which are LDO regulators. Neither have any output or input voltage. One of them takes power from the buck regulator controlled by V2AH 837 - which obviously isn't giving any output as mentioned earlier. (see blue line on attached pic - the uP7701U8 is near to the V2AF buck regulator).

The other uP7710U8 is near the PCIe (below the AMD logo) and also has no input voltage but I can't figure where it should come from - it does not connect to V2AF buck regulator, PCie 12V or EATX_12V, PCIe 3.3V or any of the G78A. However the resistance to ground from the input of this uP7710U8 - and the nearby 0R resistor which is also connected to the input pin, is quite low at 16 ohms.

I couldn't find any open circuit large SMD resistors in this area of the PCB

Maybe someone here knows what voltages should be where? It's like I have something very open circuit somewhere, stopping anything powering up at all, even 5V which should happen automatically if 12V is present.

TIA
Rich
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File Type: jpg 20211026_133446.jpg (742.0 KB, 15 views)
File Type: jpg 20211026_133702.jpg (1,011.2 KB, 19 views)
File Type: jpg 20211026_134911.jpg (594.9 KB, 20 views)
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Last edited by dicky96; 10-26-2021 at 11:16 AM.. Reason: corrected V2AH to V2AF
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Old 10-26-2021, 10:21 AM   #2
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Theres a lot of corrosion on the caps,test points and vias.Loooks pretty bad around the crossfire connector near that rusty screw
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Old 10-26-2021, 10:26 AM   #3
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Hi SMDFlea - yes I noticed that especially under the microscope - this is almost certainly air-borne corrosion. We get it here due to salty humid air near the coast. Which means just about everywhere as it is impossible to get more than about 12 miles from the ocean on this island. Plus almost nobody lives in the interior

I also noticed that there are what look like oil stains in water, around the RAM which looks like it has been overheating - unless this is normal for these GPUs. Lastly there are some odd resistance readings (but not shorts) on the Vram or Vemcontrol VRMs - I'm not sure which is which yet, but it isn't even getting as far as powering up yet, so I'm not too worried about that at the moment
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Old 10-26-2021, 10:36 AM   #4
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Can you take a close-up of the V2AH 837 part, having trouble finding it. How many pins does it have
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Old 10-26-2021, 11:14 AM   #5
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Sorry!! That's a typo

Its V2AF. I now corrected my first post.


There's a close up of V2AF in the 4th attached pic - it looks like it has 10 pins, 5 either side. And probably some pads underneath it.

Last edited by dicky96; 10-26-2021 at 11:16 AM..
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Old 10-26-2021, 11:52 AM   #6
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Quote:
Originally Posted by dicky96 View Post
Sorry!! That's a typo

Its V2AF. I now corrected my first post.


There's a close up of V2AF in the 4th attached pic - it looks like it has 10 pins, 5 either side. And probably some pads underneath it.
Its got a line above V2AF ,i think its a monolithic power part
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Old 10-26-2021, 12:08 PM   #7
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Hmm OK
Monolithic make some Buck controllers in QFN-11 and QFN-10 packages

Such as MPQ28164, MP2155, MP28163, MP28164 all of which could match this IC (as I don't know if it has a pad underneath) and all of these have maximum Vin of 5.5V which suggests it would connect to my missing 5V rail (thus telling me where it should be)

Assuming it is one of those devices... MPS normally have two lines of 3 digit codes don't they?
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Old 10-26-2021, 12:15 PM   #8
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Quote:
Originally Posted by dicky96 View Post
Hmm OK
Monolithic make some Buck controllers in QFN-11 and QFN-10 packages

Such as MPQ28164, MP2155, MP28163, MP28164 all of which could match this IC (as I don't know if it has a pad underneath) and all of these have maximum Vin of 5.5V which suggests it would connect to my missing 5V rail (thus telling me where it should be)

Assuming it is one of those devices... MPS normally have two lines of 3 digit codes don't they?
It depends on the type of package, https://www.monolithicpower.com/en/s...formation.html ,it could be V2 or V2A
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Old 10-26-2021, 03:33 PM   #9
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Quote:
Originally Posted by dicky96 View Post
Hmm OK
Monolithic make some Buck controllers in QFN-11 and QFN-10 packages

Such as MPQ28164, MP2155, MP28163, MP28164 all of which could match this IC (as I don't know if it has a pad underneath) and all of these have maximum Vin of 5.5V which suggests it would connect to my missing 5V rail (thus telling me where it should be)

Assuming it is one of those devices... MPS normally have two lines of 3 digit codes don't they?
I found a reference to it in a Radeon HD 7900 boardview (Radeon HD 7900 (C381) rev_1.00A (59YV01P0-VG0A13S) boardview.fz)

MP28115 V2** https://www.monolithicpower.com/en/d...cument_id/525/ .The marking code isn`t in the datasheet


MP2121DQ V5**
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Old 10-26-2021, 04:00 PM   #10
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Yes, most likely her marking is V2xx.
https://www.aliexpress.com/item/32818821922.html
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Old 10-26-2021, 04:11 PM   #11
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Not sure about the G78A ,the logo ive seen before, could be DiodesZetex .
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Old 10-26-2021, 04:32 PM   #12
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Default Re: Help required identifying G78A IC - Radeon HD 5870

G78a - az78l05rtr-g1
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File Type: png AZ78LXX.PNG (136.7 KB, 8 views)
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File Type: pdf AZ78L05H.pdf (256.4 KB, 5 views)
File Type: pdf AZ78LXX.pdf (768.9 KB, 4 views)

Last edited by lotas; 10-26-2021 at 04:42 PM..
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Old 10-27-2021, 03:43 AM   #13
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Default Re: Help required identifying G78A IC - Radeon HD 5870

Well done guys
So now I know the Vin pins on the V2AF. I can confirm pins 4 and 7 do connect together and connects to what must be the input capacitors to the left of the IC. Also from the datasheet the max Vin is 6V so I assume this connects to the (missing 5V rail). But I still can't figure out where the 5V supply should come from

The uP7710U8 LDO near the PCIe connector and AMD logo - the one with 16R from the Vin to ground - is supplied from one of the R23 buck coils to the right of the GPU (above Vcore VRM) that I thought may be Vmemcontrol as 16R seems about right. The other large buck coil here has 530R to ground but does not connect to Vin on the V2AF

The large buck coil to the left of the GPU (above the V2AF) has 34R to ground and this GPU has samsung memory so that also seems OK and this is most likely Vram

What is very much puzzling me - IF the G78A are fixed LDO, possibly 5V - why do NONE of them have any output voltage? They all have 12V coming in, the outputs are not connected together and all read about 4.8K to ground. This suggests they are ALL faulty and that doesn't make sense to me.

You can see some resistance and voltage measurements of this GPU on this video I just uploaded, though the video is about a GPU test rig I built and not a repair of this GPU
https://www.youtube.com/watch?v=8Kv6A-nWjNM from 11mins

Rich

Last edited by dicky96; 10-27-2021 at 03:50 AM.. Reason: corrections
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