Good after noon, best regards for 2025 to everyone in this group.
I found your group while searching the net for information on parts for a Yamaha keyboard for a friend.
I have acquired a Yamaha PSR-GX76 with a few dead keys ; D4 ,D5 , D6 ,
G#5 , G#6.I have started troubleshooting the keyboard by cleaning the circuit board and contact strip but these keys remain unresponsive.
I have done some preliminary checks that has taken me to the second circuit
board ( M/J ) and this houses the CPU. I have down loaded the service manual and trying to walk through it and for worse case scenario, I have already checked in with Yahmaha on availability of this IC or the M/J circuit
board after scowering the internet and neither had parts available.
Does anyone know how to test these ICs with a multimeter ,I want to be sure if this IC has become faulty.
I don’t think its the chip. have a look here;
its something to do with the keyboard matrix. At worst is a broken or intermittent trace. Contamination of a contact is the usual suspect.
AI Overview
To check an IC (integrated circuit) with a multimeter, set the meter to the continuity setting, then systematically touch each pin of the IC with one probe while touching other pins with the second probe, listening for a beep that indicates a connection between pins; if you hear beeps on many unexpected pin combinations, it could signify a short circuit within the IC, indicating a faulty chip; always consult the IC datasheet to understand which pins should have continuity and which should not.
Thanks for this lead,very interesting , but I do not think slapping is gonna help this baby
Taking reading where black test lead is at ground the above is the resulting
reading
CPU - XY512A00 / HD63B05V0F11P ; this is the GX76 CPU , YAHMAHA will not be sharing any data on this IC and neither does it appear on the web with data.
Good evening Trev,
I have spent several days going through the affected board which is MK 76H doing continuity testing and diode checking for broken trace and it has not been fruitful.
An alligator clip was connected to the end of the cable which goes into CN130 and CN120 on M/J Circuit Board (which host the CPU) for each individual wire to contacts test.I will be repeating this test to leave know stone unturned to make sure Circuit Board MK 76H does not have any broken or intermitent traces.
Cropped Circuit below :
Good afternoon everyone I am celebrating success today.
Yesterday ,armed with my multimeter ,hook lead ,alligator lead ,sewing needle, magnifying glass, a markerand my laptop I once more opened PSR-GX76 with a mission to find a broken trace has Midnightvisions / Trev suggested ( the Matrix ).
After a closer examination of the schematic, I had realized that all five dead keys shared traces 3 and 4 in the matrix which sends signal from circuit board MK 76H to circuit board M/J via 12 lead cable ( in this case leads N12 and N 22 ) which connect both boards.
Continuity testing from disconnected cable wire N12 along trace 3 of the matrix at all relating contacts were execellent for all 5 keys. Switching to N22 and testing along trace 4 of the matrix contacts revealed that this is where I would find the broken trace.
Adding my needle as a probe to my alligator clip tightly with magnifying glass I found the broken trace a few milimeter after the second contact after N22 enters Mk 76 H.
I tried soldering with flux after creating contact point with needle, but too tedious, so I connected with a wire to the first dead key D4.Thanks for hosting me and the significant help of Trev ,all dead keys are up and running. 
