(Topic ID: 286125)

Baby Pacman --- No Sound--- Need Help

By THE_LOCATION

9 months ago


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  • 41 posts
  • 5 Pinsiders participating
  • Latest reply 9 months ago by jj44114
  • Topic is favorited by 1 Pinsider

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C106 (resized).jpg
Vidiot sound section (resized).jpg
1K trim pot (resized).jpg

#1 9 months ago

I've hit a wall. symptom is no sound. game fully boots and plays. I have done some work on the Vidiot (new RAM chips, recapped, new 1K sound pot, resocketed and burned new EPROM at U29, replaced 6803 in the sound section. replaced Q5 in the reset section and REPINNED EVERY CONNECTOR and HEADER PINS) I get no sounds of any kind at boot. All I get is a hum in the speakers that I can increase/ decrease with the front coindoor volume knob. I get no sound at front door sound test or vidiot sound test ( I do get the 2 flashes at the LED ). Also I get the same result with an original MPU and an Altek. any help would be much appreciated.

#2 9 months ago

How many flashes on the vidiot? The vidiot has two power supply circuits on it, are they both working?

#3 9 months ago

gutz
I get 10 flashes at the Vidiot I believe (game fully boots and plays) I've checked all voltage test points on the Vidiot board. They check out.( I'm not at the game at the moment) but I believe it's 5v, non-reg 12 , regulated 12 and 8.2v.

#4 9 months ago

You need to confirm the ten flashes. Contrary to documentation, Ive seen a vidiot that skipped 1 and 2, and actually started the sequence at flash 3. I should rephrase that there are two seperate 5v regulators on the board (one for video one for sound) make sure both are working.

#5 9 months ago

When you press the sound test button on the board, do you get two led flashes? if you do, and the caps are new, I would finger probe around the op amp and the audio amp(U33 and U34). You should get some noise/hum if the amps are working.

#6 9 months ago

gutz
Thanks for the clarification. I neglected to look at it closer to know there is a separate +5v for video and sound. I've done enough work on this game so far to know there is 10 flashes ( it came to me dead and I've been painstakingly counting flashes for a while). I will look at the separate +5v!! Thanks for that

#7 9 months ago

@jj441144
When pressing the sound test button on the board I do get two led flashes. New electrolytic caps. I will definitely try your finger probe approach. Also I noticed that even though I replaced the 1K sound pot/ it doesn't make any difference to the output "hum" (this hum is constant) Note that the front door potentiometer does turn up and down "the hum". Thanks guys! hope I can get this figured out.

#8 9 months ago

Can you post a really nice picture of the Vidiot? Did you do a really good visual inspection of the board. I chased my tail on one for weeks only to find a nic in a small trace between two vias. That nic caused me to loose part of the sounds and even tho the game booted and played and the Vidiot did not see a problem.

#9 9 months ago

JT-Pinball
I read through your post about that. did that trace end up working for you?? I will post pictures tomorrow as I'm traveling for work today. Thanks again!!

#10 9 months ago

Fixed the trace and the sound worked fine.

#11 9 months ago

Double check the new pot with your meter. 1k ohms?

#12 9 months ago
Quoted from THE_LOCATION:

gutz
Thanks for the clarification. I neglected to look at it closer to know there is a separate +5v for video and sound. I've done enough work on this game so far to know there is 10 flashes ( it came to me dead and I've been painstakingly counting flashes for a while). I will look at the separate +5v!! Thanks for that

Quoted from THE_LOCATION:

@jj441144
When pressing the sound test button on the board I do get two led flashes. New electrolytic caps. I will definitely try your finger probe approach. Also I noticed that even though I replaced the 1K sound pot/ it doesn't make any difference to the output "hum" (this hum is constant) Note that the front door potentiometer does turn up and down "the hum". Thanks guys! hope I can get this figured out.

If you have counted the ten flashes (and not just assuming it has ten because the video boots) then the power supply should be fine. Pressing the audio test and getting two flashes also confirms that the problem is elsewhere.

#13 9 months ago
Quoted from jj44114:Double check the new pot with your meter. 1k ohms?

I had no change from original sound pot and replacement but will definitely check that it does spec out when I get home tomorrow

#14 9 months ago
Quoted from gutz:

If you have counted the ten flashes (and not just assuming it has ten because the video boots) then the power supply should be fine. Pressing the audio test and getting two flashes also confirms that the problem is elsewhere.

Thanks for the theory of operation as I have pressed the sound test button many times and it always flashes led 2 times. maybe I'm missing something simple I just don't know to look for. Just to note that even though I burned a new EPROM at U29 and replaced the socket for good measure, both the original and the replacement EPROM make no difference.

#15 9 months ago

It is very likely that the issue is in the analog part of the sound section. Caps, pot or amps.

#16 9 months ago
Quoted from jj44114:

Double check the new pot with your meter. 1k ohms?

jj44114

double checked the 1K pot is good.

1K trim pot (resized).jpg
#17 9 months ago
Quoted from JT-Pinball:

Can you post a really nice picture of the Vidiot? Did you do a really good visual inspection of the board. I chased my tail on one for weeks only to find a nic in a small trace between two vias. That nic caused me to loose part of the sounds and even tho the game booted and played and the Vidiot did not see a problem.

JT-Pinball
to start, here is a photo of my sound section of the Vidiot

Vidiot sound section (resized).jpg
#18 9 months ago

jj44114

I "fingured" around the U33 and U34 and got no feedback of any kind while doing so. I found that R121 looks burned as it is coming right off the non-reg 12V. it sits right above U34 but I tested it out of circuit and it checks out.

#19 9 months ago

Also just found that C106 that is in circuit before the volume pot is leaking even though it is listed as a ceramic 300pf.

C106 (resized).jpg
#20 9 months ago

I thought that you re-pinned the game? Did you re-pin the connector to the Vidiot? I had one not work just because of that...

#21 9 months ago

If C106 is shorted, Bingo...no sound. Check it with your ohm meter. Replace it in any case. a bad R121 won't kill all the sound. If its not C106 then look at U33. Do you have a logic probe?

#22 9 months ago
Quoted from THE_LOCATION:

jj44114
double checked the 1K pot is good.[quoted image]

Ok, you've measured ok across the pot, now turn the pot to about the halfway point and check the ohms between the wiper or pin1 of the pot and either of the other two pins. Should be around 500 ohms.

#23 9 months ago
Quoted from JT-Pinball:

I thought that you re-pinned the game? Did you re-pin the connector to the Vidiot? I had one not work just because of that...

JT-Pinball

I replaced all of the small .100 connectors pins and housings in the game

#24 9 months ago
Quoted from jj44114:

If C106 is shorted, Bingo...no sound. Check it with your ohm meter. Replace it in any case. a bad R121 won't kill all the sound. If its not C106 then look at U33. Do you have a logic probe?

jj44114

Thanks for helping out. Do you think a 330pf capacitor would work in place of the 300pf? I have one available at a local electronics store. I shotgun ordered a replacement last night for U33 and U34. I do have a logic probe.

#25 9 months ago

330pf is fine. We can trace the audio signal if it’s there from the DAC to to U33 and check if U33 is outputting the signal. Let me check the schematic and get back to you.

#26 9 months ago

Measure the ohms at r121. Think it should be around 200 ohms.

#28 9 months ago

Did you check if c106 was shorted with your meter?

#29 9 months ago

With your logic probe on pin 4 of U32(DAC output) you should see activity/pulsing when pressing the sound test switch on the board and when you power on the board(start up tune). Same of for pin 9 Of U33(output from the op amp).

#30 9 months ago
Quoted from jj44114:

Did you check if c106 was shorted with your meter?

jj44114

quick check in... C106 shows 390k ohms. so not a direct short

#31 9 months ago
Quoted from jj44114:

With your logic probe on pin 4 of U32(DAC output) you should see activity/pulsing when pressing the sound test switch on the board and when you power on the board(start up tune). Same of for pin 9 Of U33(output from the op amp).

jj44114

Ok, getting somewhere. Pin 4 on U32 shows activity just as you said// when pressing test button and while booting. Fun Fact// I could hear the start up tune through the logic probe lol. that was fun. Pin 9 on U33 is locked hi entirely. instant when booting and no difference when pressing the test button

#32 9 months ago
Quoted from jj44114:

Measure the ohms at r121. Think it should be around 200 ohms.

jj44114

Yes it is 190 ohms or so

#33 9 months ago

No output so Looks like U33 is the issue.

#34 9 months ago

Since you have your logic probe out. probe both sides of C111 and C112. You should get major noise out of the amp(U34), even if U33 is bad. I'm surprised you didn't get any hum/feedback when you probed around the amp with your finger.

#35 9 months ago
Quoted from jj44114:

Since you have your logic probe out. probe both sides of C111 and C112. You should get major noise out of the amp(U34), even if U33 is bad. I'm surprised you didn't get any hum/feedback when you probed around the amp with your finger.

jj44114

I was able to get a replacement locally for U33 (NTE part, which im always skeptical about NTE) also replaced C106 with a 330pf @50v cap. replaced R121 with a .5 watt for good measure. I put my logic probe on C112 and get a "Hi" on the side that connects to the volume pot and nothing on the side that connects to U34. C111 gets a "hi" on one side and I believe a "low" on the other. I get no noise out of the amp while probing caps. I still have another replacement for U33 and U34 in the mail.

#36 9 months ago
Quoted from jj44114:

With your logic probe on pin 4 of U32(DAC output) you should see activity/pulsing when pressing the sound test switch on the board and when you power on the board(start up tune). Same of for pin 9 Of U33(output from the op amp).

jj44114

Note that replacing U33, still have no change with logic probe at pin 9.

#37 9 months ago
Quoted from jj44114:

Ok, you've measured ok across the pot, now turn the pot to about the halfway point and check the ohms between the wiper or pin1 of the pot and either of the other two pins. Should be around 500 ohms.

check this.

#38 9 months ago

jj44114

Thanks for the reminder on this, I've now tested the volume pot. shows proper resistance from 0 to 1K ohm and in the middle 500 ohm.

#39 9 months ago

Here is something from pinrepair.com that might help. http://www.pinrepair.com/bally/babypac.htm

"3rd Flash.
After a pause, the 6809 CPU chip at U8 attempts to test the program EPROM at U12. This is done using a chksum routine. If the chksum is correct, the third LED flash is shown. If there is no third LED flash, the EPROM at U12 is bad (or its socket or a trace is broken going to U12)."

#40 9 months ago

jj44114 JT-Pinball

SUCCESS! replaced U34 and put in a new LM3900 @ U33(because I really don't trust NTE parts) and BOOM its up! sound test works and startup tune works. I haven't tested all the sounds yet but I feel good about it. Thank you guys for steering me in the right direction to get this nailed down!

#41 9 months ago

congrats!

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