Bradenton, FL
I am having a screeching noise through the speakers, it is a constant screech but the games music and call outs can be heard through the screeching. I'm having trouble finding a solition , any ideas as to what may be causing this?
(Topic ID: 109364)
Linked Games
Class of 1812
Gottlieb, 1991
Topic Gallery
I think I may have experienced the same problem. In my case, I would describe the noise as "garbled." It's like a steady fuzz/ distortion going constantly but the music and call outs still function like normal. Still trying to trouble shoot this issue on an Operation Thunder. Any help from out there is appreciated!
My mario is also a little garbled. It has been my experience that caps usually fix these garbled sound issues. I am going to cap mine as soon as I get my upper flipper rebuilt (this weekend hopefully) lol
the screech is from a blown aux sound power supply.
Had the following issues on my Super Mario Bros:
Problem 1: Loud Screech/hum (not the normal startup screeches) for all audio immediately when game is powered on
Resolution: Replaced the Auxiliary Power Supply.
Replacement from PBL (http://www.pinballlife.com/index.php?p=product&id=2610)
*Verify your model before ordering. System 3 uses different models for this power supply
Problem 2: Garbled Audio and Music
Resolution: Replaced the DAC (U10) and OP-AMP (U13) on the Aux Sound Board.
I socketed both chips for easy replacement in future if need be.
Getting a high-pitched dual screech at power-on is normal for Sys3. Not getting the screech indicates there is a problem in the sound circuit.
The aux power supply on Sys3 does two things: provides the +/-12vdc for the sound boards and amplifies the sound signal output to the speakers.
Depending upon the game (you didn't mention which one) there might be one sound output or two from the aux power supply (there are different aux power supplies depending upon the game). If it's two, you can disconnect one output and see if you still get the screeching. If you don't, you know it's in the amp on the aux power supply. If not, it's further back either on the aux sound board or regular sound board itself.
viperrwk
Quoted from viperrwk:Getting a high-pitched dual screech at power-on is normal for Sys3. Not getting the screech indicates there is a problem in the sound circuit.
The aux power supply on Sys3 does two things: provides the +/-12vdc for the sound boards and amplifies the sound signal output to the speakers.
Depending upon the game (you didn't mention which one) there might be one sound output or two from the aux power supply (there are different aux power supplies depending upon the game). If it's two, you can disconnect one output and see if you still get the screeching. If you don't, you know it's in the amp on the aux power supply. If not, it's further back either on the aux sound board or regular sound board itself.
viperrwk
yea the screech/hum on mine did not end, so I had blown output transistors on the aux power supply. Was cheaper to replace than diagnose it.
Not sure which aux PS board is in a Co1812 - I believe it is a MA1605. which is an earlier version of the MA1722. It uses a 7812 and 7912 to derive the +/- 12v and has two TDA2040 amps.
You can check the voltages going to the aux sound board to make sure they are correct. Do you have a manual? If the voltages check out you can disconnect one of the speakers to see if you still have the screeching. If you do, swap and see if you get it on the other channel. If you get it on both channels chances are the problem is on the sound board/aux sound board.
viperrwk
CO1812 uses the ma 1605 board. I have the manual now. I tested for voltage on the aux power supply. Pin 3 and 8 are showing 12vac from the transformer. Pins 5 and 10 are showing 0v. Something doesn t seem right. They are supposed to read +/- 12v.
It seems I should replace vr1 and vr2, would they both blow or would one blown vr cause the other to not work? The part is a 7812 and a 7912. I'll start tracking the part down. Thanks for the help thus far.
Check the four big diodes with your meter - D1-D4. The AC voltage gets rectified before it goes to the regulators. If one of them is out then you won't get any voltages. Unlikely both regulators blow at the same time.
viperrwk
I made a mistake when originally testing the +/- 12v. When I was testing the diodes I retested pins 5 and 10 on p1 of the aux power supply. I did in fact have 12v on pin 10 but no -12v on pin 5. I replaced vr2 and the sound is now working. With no screeching or feedback. Thanks for the help this problem is solved and this game has some hilarious call outs and music.
4 years later
I have a shaq I just got and I’m having sorta the same issue. All music and callouts work. Some of the game noises just screeching poping and static from the left speaker. No sound really coming from the right at all. After playing for an hour it kinda subsides a bit. Will replacing the auxiliary power board fix this? New to the pinball world it’s my first one. Thanks.
3 weeks later
Quoted from Gumby510:I will also add when I turn the game on I get one single beep. Also one of the ram at h3 has been socketed and the 6116 looks suspect. H2 has not been messed with at all. Ordered two new sockets and ram to fix this.
I am having similar problems on my #ShaqAttaq, @Gumby510. Can you share the results of your work? Thanks!!
Hi David I got your pm. I just so far have followed what info is in this thread and bought some ram for the two ram slots and a couple sockets. I lack the skills to put these in so I’m also waiting on my friend to help and see if it fixes the issue. If not I will buy the auxiliary power supply and go from there. The ram was only 18$ vs 50$ for the supply. In my case the board looks like it had been worked on before. Figure I start there. I’ll post my results when it’s done.
2 weeks later
2 weeks later
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