Intellivision sound issues

[smulz]

Hi all,

 

I'm pretty sure this isn't the place for this question, but I'm not sure where else to turn.

 

I have 2 intellivision systems, an Intellivision I and an inTV. The inTV seems to work perfectly, however the Intellivision I has some sound issues. Certain games, like Tron Deadly Discs and Astrosmash, play the wrong sound effects at times. In Tron, if the player gets hit by a disc, the sound of the Recognizer will begin playing.

 

I found this fascinating. Can anyone possibly give an explanation why this could possibly happen?

[BillyHW]

Demonic possession?

[intvnut]

Interesting. I haven't looked specifically at the code for Tron Deadly Discs. I do know that many Mattel games tend to group their sound code into one portion of the ROM. (Baseball, as I recall, has all its sound effects at the end of the ROM.) So, it could be that you've got some sort of glitch that's causing it to jump to the wrong sound effect, or it fails to terminate one sound effect and bleeds into the next, for example.

 

... glances at code disassembly ...

 

Ok, I suspect that code like this may be the culprit:

 

L_5E52:
       PSHR    R5                              ; 5E52   0275
       MVI     G_0176, R0                      ; 5E53   0280 0176
       SLL     R0,     1                       ; 5E55   0048
       ADDR    R0,     R7                      ; 5E56   00C7
       B       L_5E69                          ; 5E57   0200 0010
       B       L_5E60                          ; 5E59   0200 0005

       JSR     R5,     L_5FDB                  ; 5E5B   0004 015C 03DB

       B       L_5E69                          ; 5E5E   0200 0009

L_5E60:
       MVI     G_0323, R0                      ; 5E60   0280 0323
       CMPI    #$0028, R0                      ; 5E62   0378 0028
       BGT     L_5E69                          ; 5E64   020E 0003

       JSR     R5,     L_5FCC                  ; 5E66   0004 015C 03CC

 

Based on the value in location $176, the code wil jump to one of three distinct locations: L_5E69, L_5E60, or $5E5B. Two of them may result in sound effects being played. (The subroutines at L_5E69 and L_5FCC both play sound effects. The code branch heading to L_5E69 doesn't end up at code that plays a sound effect.) This particular piece of code picks between the two sound effects for the recognizer leaving the arena -- either the normal recognizer sound or the "bzzt bzzt bzzzzzt bzt bzzzzt" of the broken recognizer.

 

Glancing around the code, I see this idiom repeated a few times.

 

So, it smells like you might have a flaky 8-bit RAM or something. Have you run MTE-201 on this system?