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Sega Afterburner 2 Repair Log - Lack of Sound / No Sound Issue [Sega X Board]


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I had an Afterburner 2 that was initially presented with some minor graphics issues and no sound. The graphics issues were resolved through cleaning the socketed chips with some sand-paper and Deoxit. The sound issue was a bit more problematic.

 

Probing the various EPROMs, and CPUs in the sound circuit found no running logic - address and data lines were active, but stuck low or high so I went to the Z80 to test for pulse on the clock input and pin 6 was stuck high - no pulse.

 

I then probed pin 3of the 16MHz crystal - no pulse. The crystal had power but was obviously dead. I then replaced the crystal with one from another Sega X Board and got pulse to the Sega custom chip.

 

296907454_SegaAfterburnerSoundRepair.thumb.jpg.b81f4f56312ed48f17615ac3a859a465.jpg

 

The Z80 also regained pulse on pin 6. Although there was now sound, but it was a bit messed up as you can hear in the following video;

 

 

Given some of the corrosion issues elsewhere on the board, I did a quick visual inspection. IC11, and IC13 which are 1Mb, 28 pin Mask ROMS looked like likely culprits, especially given that some of the sound was working and IC12 looked fine. I removed and cleaned these chips again, but it didn't change the sound. I decided to do checksum test on the Mask ROMS and quickly found IC11 and IC13 to either not read consistently or return different checksums on each read. As my programmer doesn't read non-JEDEC files, I had to make an adapter and read these 28 pin Mask ROMs as 27C1001s. I had made an adapter for 27C1000s previously, but also had to jump the VCC line to pin 28 on the mask ROM.

 

 

 

Using the MAME set, I re-programmed IC11 and IC13 using some 27C1000s (non-JEDEC). Just as an FYI, you don't need to make adjustments to the X Board's jumpers to do this. If you were to used JEDEC size 1Mb EPROMs, then you would need to modify the board.

 

Anyway - sound issue now fixed!

 

 

 

 

 

 

20200617_161228.thumb.jpg.46e00ff1970920080f99b347be55f14a.jpg

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