Star Trek 25th Sound problem

[Bill]

I have a ST 25th with a weird sound problem. Briefly, whenever it is in multiball, as targets are being hit, the sound will suddenly go off. Then the usual sounds will be replaced by a series of tones, hums, or static pops until the balls are lost. Then the sound will go back to normal. This never happens in single ball play.
I have switched out the sound board (used original sound roms), ribbon cable, power supply, and checked the entire game for loose or broken diodes with no improvement. Any suggestions on what to look for? Could it be the sound roms? Game Roms? It has a Rottendog MPU and Rottendog power supply. Any help appreciated. I am LOST!

Also, I switched in a DE star Wars MPU and that did not work at all. I thought that should be interchangeable. Then, when I put the MPU back in Star Wars, it played fine for a game or two, but about 20 minutes later, the game went down. The board will not power up. The 5v and PIA lights stay lit constantly. Coincidence or did I screw something up? Any thoughts on what to look for on that as well?

[John Robertson]

On 2021/04/05 5:56 p.m., Bill wrote:
> I have a ST 25th with a weird sound problem. Briefly, whenever it is in multiball, as targets are being hit, the sound will suddenly go off. Then the usual sounds will be replaced by a series of tones, hums, or static pops until the balls are lost. Then the sound will go back to normal. This never happens in single ball play.
> I have switched out the sound board (used original sound roms), ribbon cable, power supply, and checked the entire game for loose or broken diodes with no improvement. Any suggestions on what to look for? Could it be the sound roms? Game Roms? It has a Rottendog MPU and Rottendog power supply. Any help appreciated. I am LOST!
>

I don't recall this sort of thing with a Whitestar MPU so I suspect that
RD may have done a shortcut in their chip choice that is leading to the
problem. I've seen that before.

Look for 74HCxx chips instead of 74HCTxx chips inthe audio circuits.
That was the cause of the last RD problem I ran across - the wrong TTL
family.

> Also, I switched in a DE star Wars MPU and that did not work at all. I thought that should be interchangeable. Then, when I put the MPU back in Star Wars, it played fine for a game or two, but about 20 minutes later, the game went down. The board will not power up. The 5v and PIA lights stay lit constantly. Coincidence or did I screw something up? Any thoughts on what to look for on that as well?
>

That I'm not sure about, and it is late and too tired (and too much
wine) to do a proper schematic check. If the MPUs are the same part
number then they should work. Beyond that would require more thought
than I am capable of at this time...perhaps the RAM is not correct? 6116
vs 6164 for example???

Sorry!

John ;-#)#


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[Bill]

I am about ready to throw it all in on this Star Trek 25th! I still am experiencing the SAME sound problem! It usually occurs on multiball but not always. The sound suddenly goes out and is replaced by static pops, cracks, and heavily distorted sounds. After the ball drains, the sounds come back as normal.

I have had in the game 2 different MPU boards, 2 different sound boards, 2 different power supplies, I have repinned the power board for the 12v wire, and have even replaced all sound roms and main game rom with new chips. It still doesn't freakin' work! I even subbed in a different ribbon cable from a Star Wars to see if that made a difference. It didn't.

There are no obviously broken coil diodes or burned coils. Everything on the game appears to work perfectly except for this intermittent sound problem.

Anybody have any thoughts on where to go from here? This game is INCHES from being stripped and sold for parts.

[John Robertson]

On 2021/04/28 10:35 a.m., Bill wrote:
> On Tuesday, April 6, 2021 at 12:52:11 AM UTC-4, John Robertson wrote:
>> On 2021/04/05 5:56 p.m., Bill wrote:
>>> I have a ST 25th with a weird sound problem. Briefly, whenever it is in multiball, as targets are being hit, the sound will suddenly go off. Then the usual sounds will be replaced by a series of tones, hums, or static pops until the balls are lost. Then the sound will go back to normal. This never happens in single ball play.
>>> I have switched out the sound board (used original sound roms), ribbon cable, power supply, and checked the entire game for loose or broken diodes with no improvement. Any suggestions on what to look for? Could it be the sound roms? Game Roms? It has a Rottendog MPU and Rottendog power supply. Any help appreciated. I am LOST!
>>>
>> I don't recall this sort of thing with a Whitestar MPU so I suspect that
>> RD may have done a shortcut in their chip choice that is leading to the
>> problem. I've seen that before.
>>
>> Look for 74HCxx chips instead of 74HCTxx chips inthe audio circuits.
>> That was the cause of the last RD problem I ran across - the wrong TTL
>> family.
>>> Also, I switched in a DE star Wars MPU and that did not work at all. I thought that should be interchangeable. Then, when I put the MPU back in Star Wars, it played fine for a game or two, but about 20 minutes later, the game went down. The board will not power up. The 5v and PIA lights stay lit constantly. Coincidence or did I screw something up? Any thoughts on what to look for on that as well?
>>>
>> That I'm not sure about, and it is late and too tired (and too much
>> wine) to do a proper schematic check. If the MPUs are the same part
>> number then they should work. Beyond that would require more thought
>> than I am capable of at this time...perhaps the RAM is not correct? 6116
>> vs 6164 for example???
>>
>> Sorry!
>>
>> John ;-#)#
>>

> I am about ready to throw it all in on this Star Trek 25th! I still am experiencing the SAME sound problem! It usually occurs on multiball but not always. The sound suddenly goes out and is replaced by static pops, cracks, and heavily distorted sounds. After the ball drains, the sounds come back as normal.
>
> I have had in the game 2 different MPU boards, 2 different sound boards, 2 different power supplies, I have repinned the power board for the 12v wire, and have even replaced all sound roms and main game rom with new chips. It still doesn't freakin' work! I even subbed in a different ribbon cable from a Star Wars to see if that made a difference. It didn't.
>
> There are no obviously broken coil diodes or burned coils. Everything on the game appears to work perfectly except for this intermittent sound problem.
>
> Anybody have any thoughts on where to go from here? This game is INCHES from being stripped and sold for parts.
>

Is your board a RD or factory? You might be best to send it off to a
qualified service shop to get to the bottom of the problem.

Without sophisticated service tools one is shooting in the dark
here...we fix these boards as do others.

[Bill]

I've had two DIFFERENT MPU boards in it. One RD, one factory. Two different sound boards in it. Two different power supplies in it. Same problem with both.

[John Robertson]

> I've had two DIFFERENT MPU boards in it. One RD, one factory. Two different sound boards in it. Two different power supplies in it. Same problem with both.
>

Hi Bill,

Rereading the above I see you never checked the MPU and sound ROMs. If
you have an EPROM burner that is what I would do now...

I'll assume you checked/exchanged any audio cables.

[Bill]

I actually had a guy burn all new sound roms and game roms. Made no difference.

I did notice however that when the sound goes off in multiball, it will continue clicking and humming if I pick up the balls and hold them in my hand. (Playing with the glass off.) If one of the balls drains, the sound will still stay off/distorted. The minute the SECOND ball drains, leaving only 1 ball still in play, the sound is restored to normal. So basically, sound goes out during 3 ball multiball, stays out when 1 ball drains, but is restored to normal when the 2nd ball drains. The only thing I noticed on my game is that 2 of the trough switches are large white microswitches, but the third microswitch is a small black one. The diode is wired differently on this one with the non-banded side going to common, unlike the large white micros where the non-banded side does not go to common. But, several other switches (shooter lane) use the same switch wired the same way. So either that is normal or somebody replaced a bunch of switches incorrectly. (Possible but maybe unlikely?)

[John Robertson]

> I actually had a guy burn all new sound roms and game roms. Made no difference.
>
> I did notice however that when the sound goes off in multiball, it will continue clicking and humming if I pick up the balls and hold them in my hand. (Playing with the glass off.) If one of the balls drains, the sound will still stay off/distorted. The minute the SECOND ball drains, leaving only 1 ball still in play, the sound is restored to normal. So basically, sound goes out during 3 ball multiball, stays out when 1 ball drains, but is restored to normal when the 2nd ball drains. The only thing I noticed on my game is that 2 of the trough switches are large white microswitches, but the third microswitch is a small black one. The diode is wired differently on this one with the non-banded side going to common, unlike the large white micros where the non-banded side does not go to common. But, several other switches (shooter lane) use the same switch wired the same way. So either that is normal or somebody replaced a bunch of switches incorrectly. (Possible but maybe unlikely?)
>

I can't see the trough switches affecting the audio. Either the machine
knows the switches are closed or that they are open. The CPU then knows
how many balls are wandering around the playfield.

Is the sound board part of the MPU or separate? If separate did you
check the interconnect cable for continuity?

I'll have to pull out my schematics next!

[Bill]

Sound board is separate from the MPU. Both the sound board and MPU were replaced with other boards but the problem remained. Also the ribbon cable from the MPU to the sound board was replaced but the problem still occurs. It almost seems like the problem is somewhere somehow on the playfield, as unlikely as that seems. I even unhooked the lower speaker and front speakers one at a time to see if that had an impact but it didn't.

[John Robertson]

> Sound board is separate from the MPU. Both the sound board and MPU were replaced with other boards but the problem remained. Also the ribbon cable from the MPU to the sound board was replaced but the problem still occurs. It almost seems like the problem is somewhere somehow on the playfield, as unlikely as that seems. I even unhooked the lower speaker and front speakers one at a time to see if that had an impact but it didn't.
>

We expect to be overhauling a DE-ST in the next few months if you want
to send the boards to us to see if we can duplicate the problem...email
me directly about shipping requirements unless you are in Canada and
thus have no customs clearance to deal with...your problem is certainly
weird.