(Topic ID: 247868)

Xenon no sound....help appreciated.

By Sonora70

1 year ago

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  • 55 posts
  • 9 Pinsiders participating
  • Latest reply 1 year ago by EdHess
  • Topic is favorited by 2 Pinsiders


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#3 1 year ago
Quoted from Sonora70:

The speakers are completely silent.

No pop from the speaker on powerup?
When you adjust the volume pots on the sound board, you getting any scratchy noise through the speaker?
With the machine off, measure the resistance between ground and the negative lead of capacitor C8 on the sound board. If you're not reading low ohms then it's a problem with the speakers or connection to them.

#9 1 year ago
Quoted from Sonora70:

Got a reading of 109.9 ohms.

Schematic doesn't show it but if your Xenon has a volume control inside the door, 100 ohms resistance is about the right reading (since it's a 100 ohm volume pot). Have you tried sweeping this coin door volume control full swing to see if you get any sounds/crackling through the speakers?

The game has two 8 ohm speakers and from memory they're wired in parallel, or could it be in series? Can't remember. If they're in parallel you should measure approx 4 ohms across the two speaker wires coming from the harness that connect to the speakers, otherwise if they're wired in series you should measure 16 ohms across those two wires.

One of those two wires connecting to the speakers is ground (with the machine off confirm one of those wires measures zero ohms resistance to ground), the other wire comes from the volume control.

#11 1 year ago
Quoted from Sonora70:

The speakers are connected together, I believe in series because the second speaker is pigtailed off the first.

Can you post a picture of the speaker setup? And clear high res pictures of the sound/vocalizer boards?

Once you're sure the speaker setup is right, carefully check that the TDA2002 amplifier (U9 connected to the heatsink) on the sound board has 12V power at pin 5.

Also grab a screw driver and touch the + leg of capacitor C5 (which goes to the input of the amplifier) with the screw driver tip while holding the metal part of the screw driver. Do you get any speaker hum?

#15 1 year ago

Those door volume pots often go flakey.

So it looks like the orange wire to the speaker is ground.
The white wire to the speaker comes from the coin door volume pot.
Measure the resistance from the white wire back to the negative lead of capacitor C8 on the sound board. As you adjust the volume control on the door the resistance reading should change from zero ohms when set to max volume to 100 ohms when set to minimum volume. If you're getting readings way beyond 100 ohms, it's likely the swiper arms inside the volume pot is going open circuit.

You can buy a replacement volume pot from Jameco:

Or you can fix yours. It's held together by 4 tabs. Bend the tabs up so the volume pot assembly comes apart. Bend the four internal swiping arms out a little so they make better contact. Clean the centre ring that the inner swiping arms touch. Then put it all back together.

#18 1 year ago
Quoted from Sonora70:

One thing I noticed is the orange wire is connected to the post with a + on it on both speakers.

That's funny. Normal practice is to wire ground the the "-" lug. So long as it's connected to the same lug on both speakers it's fine. The problem comes when the wires are crossed on one speaker because as one speaker pushes out, the other speaker will pull in and sort of cancels the sound.

BTW, those speakers are wired in parallel.

#28 1 year ago
Quoted from jj44114:

They should be wired in series, they are now wired in parallel which gives 4 ohms to the amp. Might have blown the audio amp.

The parallel wiring in that picture on those speakers looks factory. The TDA2002 amp is designed to drive loads down to 1.6 ohms, so a 4 ohms load isn't going to blow it. Remember the speaker load is hanging off the 100 ohm wirewound volume pot anyway so under normal circumstances the amp won't see a load that low.

OP, are you reading 100 ohms at the output of the sound board no matter where you have the coin door volume set?
When the coin door volume is at max volume position you should read 4 ohms. When the pot is at minimum volume you should read 100 ohms. The resistance reading should change as you adjust the volume.

If you always read 100 ohms no matter where the volume pot is positioned, it says you've got an open circuit between the volume pot and the speakers, or both speakers are open circuited (unlikely for two of them to go but still possible).

#30 1 year ago

Cool, ok the speakers are out of the way now.

What voltage do you measure on the "+" leg of capacitor C8 on the sound board? That's essentially output of the TDA2002 amplifier and it should be about half the voltage you measured at the power pin (pin 5) of the amplifier. Pin 5 was previously measured at 15 volts, so the + leg of C8 should be around 7.5 volts.

#32 1 year ago
Quoted from Sonora70:

Does that mean a bad amp?

Pretty likely.
Check the input signal voltages to the amp. Pins 1 and 2 should also be about half the amps power supply voltage.
For easier access, the "+" leg of capacitor C5 goes to pin 1 of the amp, and the "+" leg of capacitor C7 goes to pin 2 of the amp.

BTW, you should also check if any of C5, C7, C8 or C25 are shorted.

#34 1 year ago
Quoted from Sonora70:

Checked input voltages. + leg of C5 is .14 VDC. + leg of C7 measures .06 VDC. Pin 5 of the amp still measures 14.9VDC.

The input and output voltages at the amp should be centre biased (half the power voltage). You're getting zero volts on each. It's time to replace that TDA2002 amplifier chip at U9 on the Sound Plus board. BTW does the heatsink it's attached to get warm after a few minutes of being on?
Inspect the back of the board when you pull it out around the amplifier for anything that looks obviously wrong (damaged).

#36 1 year ago

Good luck, let us know how it goes.

#39 1 year ago
Quoted from jj44114:

If those speakers were wired in parallel from the factory then it was a mistake. I Have seen many games from that era, always wired in series. And... a 4ohm load will blow a 40 year old TDA2002 at full volume.

Mistake? Mmm, nah. 4 ohm load is fully within spec of the TDA2002.
Another factory parallel speaker wiring pic from "the-dirtiest-xenon-on-planet-earth" thread.


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