What's new
By:

Irem m92 no sound

B

brad808

Professional
Joined
May 1, 2016
Messages
367
Reaction score
398
Location
Ontario Canada
Bought an m92 board that was sold as "working" but appears to have no sound. Board is clean with no obvious corrosion. I've replaced all the old Elna caps. Vr1 is working. Amp appears to be working as I can hear hum coming through and getting louder when I touch. Any suggestions on what to check next?
 
For first try to figure out if lack of sound has digital or analog cause.This is up to your troubleshooting skills and equipment.I recommend you to get an audio probe, with this it you will pinpoint the nature of the fault in few time.Obviously I suggest you to check with a logic probe the digital circuit to see if system is properly running.
 
a cheap test is to turn the volume all the way up and if you heard some speaker buzzing it's usually a good sign that the amplifier is working and the problem is further up-stream.
 
twistedsymphony said:
a cheap test is to turn the volume all the way up and if you heard some speaker buzzing it's usually a good sign that the amplifier is working and the problem is further up-stream.
Click to expand...
He already said the amp is doing its job so probem is elsewhere.
 
caius said:
For first try to figure out if lack of sound has digital or analog cause.This is up to your troubleshooting skills and equipment.I recommend you to get an audio probe, with this it you will pinpoint the nature of the fault in few time.Obviously I suggest you to check with a logic probe the digital circuit to see if system is properly running.
Click to expand...
thank you. I have logic probe to start with digital audio check. Can you outline where I'm probing?
 
check the volume pot is actually good, i'v seen those bad a couple of times.
 
Darksoft said:
you will see that pin 21 is the output that goes to the D/A (which is the YM3014). I would check if there is proper output there.
Click to expand...
I checked pin 21 tonight of ym2151 and am getting pulse there. Is there schematic for this board anywhere?
 
No schematics unfortunately. But well known, is this a conversion or original ROMs? If it's a conversion and you have the wrong sound CPU you'd be missing sound.
 
Are they still the original caps around the sound section?
If so then it is a good bet that 1 or more of these are bad and certainly some of them can pretty much make the board seem audio dead. I did repair one a few weeks back for a friend though it was quiet and crackly, took 5 caps.
 
Usually the one that can mute a board is the bigger capacitors which filters the +12V.But if you have already replaced it, that's not the problem.As I sad, you must determine if fault has analog or digital cause (very simple using an audio probe) then you have to troubleshoot it.
 
Last edited:
Maybe you can help me since I'm not familiar with an "audio probe"? I'm not used to fixing this style board and with no schematic it's more difficult. Can you give me few spots to check? Thanks

9zyVVeu.jpg


1mZFmM4.jpg




5DcdNdU.jpg
 
Last edited:
An audio probe is simply an external amplifier, you can "listen" with it diferent points of the audio circuit like OP-AMP input/output and DAC output, etc..
Anyway, for first check with you scope if serial data are coming out the YM2151 (pin 21) and if analog converted signal is outputted by the YM3014 (pin2).Obviously dump the two sound code ROMs on ROM board and check if the NECV35 sound CPU is well inserted in the PLLC socket.Please, report also the part number stamped on the sound CPU.
 
Last edited:
I probe ym2151 pin 21 and see it's output. I probe y3014b and see input but no analog output on pin 2. I pull a working y3014b from P.O.W board where I can see input and output fine, swap into m92 and see input and no output still (same result)? Here is sound cpu
gf2PqKA.jpg
 
I had the fujitsu amp crap out on one of my M2 boards and just picked up a new one off ebay and slapped it in and it was good to go. Hate those old fujitsu ttl, ram, and amps :/
If not that, just curious if you did a visual inspection of the board top and bottom for trace cuts?
 
Did you dump the two sound code ROMs?If not, you should do it in order to see if code is valid.
 
You must log in or register to reply here.
Back
Top