Aug 172017
 

Received some Irem 92 boardsets mostly for replacing preventively the infamous ELNA brown electrolytic capacitors but two of them were faulty too.

The first was a Cross Blades (japanese version of Blade Master!), board had green ELNA capacitors so no strict need to replace them.

But it suffered from sprites isssue, they were missing some parts:

Pressing the board in the area of ‘NANAO GA22’ custom ASIC restored the sprites :

A closer inspection of this custom revealed three liften pins :

 

Reflowed them fixed the issue :

The second board was Hook (World version)  :

Game booted up but sound was missing, I could hear only a rustling noise.Besides, video had some interferences:

Usually the two issues are strictly related, the cause is some bad electrolytic capacitor in audio circuit which affects video output too.The board mounted ELNA brown capacitors which are well known to age poorly.Sure enough :

The 470uF 25V @C202 was clearly leaking, this capacitor is used as filter for the +12V for the amplifier, this explained the issue.Measuring it out of circuit confirmed it was bad with an increased ESR of 150 Ohm :

I replaced this and all other electrolytic capacitors, this fixed board completely:

Here’s for reference the capacitors list with value and location :

C201 1uF 50V
C202 470 uF 25V
C203 220uF 10V
C204 22uF 25V
C209 100uF 25V
C210 1uF 50V
C213 47uF 16V
C215 1uF 50V
C216 1uF 50V
C217 1uF 50V
C218 1uF 50V
C219 1uF 50V
C236 100uF 25V

You can find it in our document section too : 

http://www.jammarcade.net/files/Documents/Irem_’M92-A-B’_CPU_board_electrolytic_capacitors_list.pdf

 Posted by at 11:05 pm

  6 Responses to “Irem M92 double repair log #2”

  1. Hi Caius! Amazing work! I’m Sergio and I’m from Spain.

    Recently I’ve got an “In The Hunt” M-92 board that have no sound at all. Video works perfectly but any sound outs from board (neither music nor fx).
    I’ve kept the game running for quite a few minutes and the general sound amplifier has not even warmed up a bit.
    This seems a little strange to me and I suspect that the amplifier itself is broken. I tested it and power arrives perfectly to the amplifier (5V and ground are connected properly).

    Is it possible that it is an amplifier problem? or could it be produced by another component around it, like a condenser?

    I have to say that this board also has brown ELNA capacitors, but inspecting them carefully I haven’t seen them leaking at all (yet…)
    I also plan to change them near in the future to avoid future leaking.

    Can you help me? Thanks in advance!

  2. Hi,
    first of all you should determine if the lack of sound has digital or analog nature.This is up to your hardware knowledge and skills.You may “listen” the audio circuit with an audio probe to see if sound is correctly generated but then lost somewhere.Try also to swap a good known motherboard to se if fault lies on this or on ROM board (if on ROM board, then the cause lies in digital circuit).Have a good job!

  3. Hi! Thanks for your quick response!

    I don’t have any other Irem M-92 board to swap, so I will try to test if audio is correctly generated.
    I have no Audio probe gadget, so I will try to connect a pair of auto-amplified PC speakers to the output of Yamaha DA Converter mounted in this motherboard (I think is a Y30148) to see if at least the music from Yamaha FM YM2151 (not the sound fx) are generated correctly.

    Is there any risk in doing this?

    I think the problem is located in analog audio circuit, because it would be very strange if both sound generators (Yamaha and Nanao) failed simultaneously.

    Thanks!

    • No risk using the audio probe unless you will short something.For digital cause I’m not meaning only a faulty IC, don’t forget that all the sound system is ruled by the NEC V35 CPU and if a problem occurs in its busses you will end up to have no sound (both music and sound FXs) 🙂

      • I just checked audio signal just before audio amp with an audio probe and… voila! audio signal reaches the amp.

        Then I checked voltage through audio pins at jamma edge and it surprise me… It outs about 4 volts… to much for an audio signal (even amplified).
        I tested that signal with audio probe and is a “super” – amplified signal (I need to drop down the audio pot almost to min to not hear it distorted)

        The thing is that the problem is between audio pot and jamma edge. This means that it can only be the amplifier or the large capacitor at its side. there are no more components until the output.

        That capacitor 470uF is suspicious to me…

        With these symptoms, can it be possible to be the reason of the problem?

        I plan to recap all the board, so soon we have a response… 😉

  4. Before replacing all capacitors, measure the ESR with a proper meter.(if you have it).If you look, you will find!