Sega System 32 Motherboard: No sound

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
So I'm trying to figure out why there is no sound coming from the motherboard. When I do a RAM test, it comes back with IC16 is bad and all the rest are fine. The IC16 is located right by the audio area/Z80, so I thought that could possible be the trouble. However, I replaced it and the problem remains...it still comes up bad as well. I used a known good replacement.

 

aha2940

AH, A, COLUMBIAN!,
Joined
Dec 15, 2013
Posts
2,528
Hi

If the IC reported as bad was replaced and the problem remains, then I would check the traces going to/from that IC and the rest of the sound system. I am not familiar with this board in particular, but that's what I would do.

Regards.
 

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
I forgot to mention that the traces looked good too..not even a single suspect one.
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
What kind of chip is IC16 exactly? It's likely the Z80 is failing.
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
Also check if there is at least a hum, if no hum the the output caps could be bad, bad amp, bad potentiometer etc.
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
http://www.datasheetarchive.com/dlmain/Datasheets-16/DSA-317071.pdf

That's the chip. When I turn the audio on, I hear a crackling sound and that's about it.

If it's saying the SRAM is bad and you replaced it and nothing changed then you need to check the control lines on the SRAM.

20 - CS1 (Chip Select)
22 - OE (Output Enable)
27 - WE (Write Enable)

They are all active low so if any are high then they aren't active but if any are just dead then you have a problem somewhere else. You can then trace to see what they connect to, most likely a TTL chip.
 

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
Yeah, all 3 of them are active high.
 

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
Check what they are connected to.

20 goes no where, 22 goes to Sega Custom 315-5385, 27 goes to Sega Custom 315-5385 as well
 
Last edited:

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
Alrighty, I'll give that a shot. Thanks
 

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
Question, even if the reset on the z80 registers as high, could the z80 still be the problem?
 

Fox1

Bub & Bob's Bubble Buddy,
20 Year Member
Joined
Feb 24, 2001
Posts
3,169
Okay, I'll give it a shot tomorrow. Need to go buy a mount for it.
 

miisalo

Astra Superstar
Joined
Jan 3, 2014
Posts
669
I have the same problem, socketed the IC16, replaced with a chip that _should_ work (I have same as original chip coming soon). I was suspecting the Z80 too. This is the clock signal for Z80

17115317528_835f74f599_c.jpg

The other 8Mhz signals coming from the buffer/driver chip look fine, so either something weird is happening in the Z80 or one of the outputs of that clock driver is done.

Reset stays high.

I remember seeing something weird in the address lines, going to scope them now.
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
Does the Z80 at least register low during power up for a split second? If it doesn't the you need to check the reset circuit.
 

miisalo

Astra Superstar
Joined
Jan 3, 2014
Posts
669
It's low and jumps to high with tiny delay, so reset circuit should be fine. Scoped address lines and all but A0 jumps between low and high.
 
Last edited:

miisalo

Astra Superstar
Joined
Jan 3, 2014
Posts
669
Installed socket and another Z80. Now I can sometimes hear few cracks when powering the board. Same damn problem that fox has...
 
Last edited:

mainman

CPS2 Person.,
20 Year Member
Joined
Mar 26, 2001
Posts
3,721
Damn it, Damn it. I fixed this problem before but can't remember what the cause or solution was.
 

miisalo

Astra Superstar
Joined
Jan 3, 2014
Posts
669
Hopefully you remember in some point. I'm going to scope a bit to see if I find something weird. I do have 32 channel logic analyzer too.

Edit: that clock signal is shit but works, using another source pin, signal is better but same problem. Also noticed that without Z80, system does not boot at all.
 
Last edited:

miisalo

Astra Superstar
Joined
Jan 3, 2014
Posts
669
I installed exactly same as original sram and while pressing some of the chips I got corrupted sound and IC16 actually passed the test few times. I have now reflowed three custom chips but still no sound and IC16 is bad again.

The board is quite badly bent so it's probably at least partly issue with solder joints...
 
Top