Repair of ASUS H81M-A 4th Generation
This ASUS Motherboard H81M-A Rev.:1.03, 4th Generation was brought to the Workshop because it was fully dead.
First of all, the boardview of this Mobo was open and the repair began. An energized SMPS was connected and the +5VSB (Standby) were present. In this diagram these +5VSB was supplied for the SMPS.
Next step was to check the +3VSB, which was generated by LDO REG. AZ2085D, PU601 in the diagram.
This voltage was present, so far so good, but when the Mobo was switched on by jumping pins 6 and 8 of the F_Panel it started in a bucle way, it was a bad sign, of course.
The v-out of the different power supplies had to be tested by order. The first was the RAM, 1.5v were present. Next power supply that should be taken into consideration was the N-MOSFET PH7730DL (P701), and a strange behavior was occurring right here. Let´s analyze next photo.
In the Drain of PQ701 the +1.5VDUAL supplied by PU502 LIN REG. RT9045GSP was present, so far everything was fine. But this MOSFET had no v-out in the source pins (pins 1; 2 and 3). By analyzing the circuit, there was a fatal error, the gate had no polarization.
This voltage should be supplied by PU701, the OP AMP. GS358ASF, in the pin 3 of this IC there was 1.04v (as shown in next picture), but not voltage in the pin 2
This IC acts as a comparator, but it was not performing like this, so it was changed by a new one. Now the mobo started and the PCH was supplied with 1.05v, but the system turned off and no bucle. A new behavior appeared at this time so it was time to check the PWM CONTROLLER ASP1258QGJ-A (PU101)
In the pin 2 (P_VCORE_VCC5_20) of this IC there was +5v, but in pin 1 (P_VCORE_EN_10) there was no voltage. By analizing the circuit there was a transistor in bad conditions, switching on not in the right moment and conducting the +3.3v of enable to GND.
This transistor was PQ802 in the diagram: NPN METR3904-G. It was changed and everything got to normality as usual.
Thermal compound for the UP, preventive maintenance to the mobo and it was tested for 3 days in a row without any malfunction.
Double satisfaction: for the owner and for me. Mission accomplished.
This article was prepared for you by Humberto Rodriguez, one of our ‘Master Authors’ from Cuba.
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You may check on his previous article on UPS-SL650 Repaired
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Parasuraman S
May 4, 2025 at 3:53 pm
Hi Humberto! Nice to see an article from you after a very long time! How are you? The information shared was very useful and many thanks for it, dear!
Humberto
May 4, 2025 at 9:18 pm
Hi, Parasuraman. You are right, a long time out, but I'm in again. Nice to share articles again.
Yogesh Panchal
May 4, 2025 at 4:22 pm
Humberto Rodriguez,
Glad to see you after so long time,very informative repair steps i used this model ASUS H81m motherboard with Celeron CPU (supports 4th gen CPU) for more than 10 years very good quality of Motherboards.
Humberto
May 4, 2025 at 9:21 pm
Hi Yogesh, thanks for replying. In my country the 4th Generation is still very used, and in my own opinión, very good quality with this old PC's Generation.
Albert van Bemmelen
May 4, 2025 at 6:02 pm
Hi Humberto! An excellent article after a long time! And a very complex repair too!
That you only were able to master with the help of a mainboard schematics tool.
And without it is hard to find the cause of any problem.
I notice you used Boardview which made finding the culprits possible which is often also used with other boards like those complex boards from Apple. I have never used any of those tools yet, also because Apple replacement parts are impossible to get. (And if we do only from second hand used boards). And most Apple components are special marked semiconductors always preceded by the word "critical"! Which also means that no other parts qualify for replacing those mainboard components.
My shopowner friend however uses that Boardview tool for the Apple laptop repairs he tries to fix. But to me it seems to be a lost cause because Apple is a service unfriendly firm!
Humberto
May 4, 2025 at 9:28 pm
Hi Albert, I confess this repair was not so easy. Thanks to Boardview I could finish the repair satisfactorly. I've been studying PCs and Graphics Cards repair for a long, but I only have repaired only one Graphics. Sometimes the spare parts are hard to get in my country. Well , glad to be here again.
Mark J
May 5, 2025 at 12:33 am
Humberto great article very informative. Thank you for sharing.
Humberto
May 5, 2025 at 9:46 am
Thanks Mark
Henrique Jorge G. Ulbrich
May 5, 2025 at 12:38 am
Ola, Humberto. Me complace mucho verle de vuelta. Sus reportes de mantenimiento siempre han sido muy apreciados. Saludos de Brasil.
Hi, Humberto. Nice to see you again. Your maintenance reports were always too appreciated. Greeting from Brazil.
Humberto
May 5, 2025 at 9:45 am
Thanks Henrique, I am glad to be back again.
Waleed Rishmawi
May 5, 2025 at 2:58 pm
thanks for all the provided information needed for this repair. good to have you back. be blessed.
Humberto
May 6, 2025 at 9:39 am
Thanks Waleed