(Topic ID: 24704)

Data East speaker noise - ideas for a cure


By roc-noc

7 years ago



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#23 6 years ago

I've solved this many times before.

Your -12v rectifier is bad on the power driver board.

It supplies only the sound board. The sound board will work without it, but it will sound like shit and hum. Easy to test.

#26 6 years ago

I don't have the schematics on hand, but there is a -12v test point on the sound board and or the driver board. It is supplied by a single rectifier and fuse(likely). Other than the caps as suggested above, this is one nobody expects. It's a cheap part and common. It supplies the negative rail for the amp.

1 week later
#41 6 years ago
Quoted from Crash:

Can someone get castlesteve back in here? Can't figure out what he's talking about but he may be on to something.

Sorry, I totally missed these updates.

The -12v is created by a bridge rectifier on the power supply, not the sound board. However I believe much of the sound problems you all are hearing is probably with a working machine.

So there are other options. In the car audio world, we heard line level noise all the time due to floating grounds and various motors making electrical noise (remember when your mom used to run the vacuum and the tv would go crazy).

This can be solved by using an automotive line level filter. It would have to be modified - or rather - the pinball wiring would have to be modified to plug into it. It's a possibility. Another option would be to further isolate the wires running to the audio board and put ferrite cores on them.

I now have a de that I brought into my personal game room that all of a sudden makes audio noise that didn't in another location. You could also try using a UPS as a cheap AC line conditioner.

I'll try some things and report back

#43 6 years ago

Well moving components around in the backbox and adding ferrite cores did not work. So the source of noise is not likely created from their own components or non- shielded data. I'll try next an AC line conditioner and see if the noise is making it in that way. I doubt it though as transformers act as a line conditioner by themselves.

Next ill search for AC ripple on the amp rails. It better be clean

#45 6 years ago

update...

Ok, so I have a high end AC line conditioner and I tested before and after and made measurements as well.

Without: measured from the TPs on the power supply, I was getting 300mV of AC ripple on the +12V output. About 50mV of ripple or less on the +5v and -12v outputs. So that's pretty low.

With the AC line conditioner, it measures the same. So we can rule out noise introduced from outside.

So, now we need to look at quieting down the output of DB1 (CM3501) on the power supply. It has a bank of capacitors C11 - C14 used to smooth out the output of the bridge rectifier. BTW, this is also the same rectifier that creates -12V... and I've seen where half of this rectifier fails before - which was my original post response.

The output of this rectifier is labeled un-regulated +12V. I measured it around 11.05V which is fine. It's called un-regulated because it still has noise on the line and the other circuits that use it are responsible for regulating and smoothing the input. So we can look at either the sound board to smooth out this voltage or smooth it out right at the power supply.

Again, this may not solve the problem, but my next guess. I have a bench power supply that hopefully can supply enough voltage and i'll drop that into the circuit to see if that cleans up the hum. If so, then we can just add the right capacitors to the power supply and if necessary make an inline connector for people to drop in to fix the hum. That's the aim anyway

#51 6 years ago

Agreed. I don't like seeing 300mV ripple in the +12v line, but I haven't measured it at the amp yet

#53 6 years ago

I believe we are on the right track then. I also think I can create a simple inline connector for those who dont want to bother with soldering etc.

#57 6 years ago

I have a solution. I'll be testing it tonite... just scrounging my parts bin for the right items. Maybe RadioShack will have what I need. I've cross referenced it with 3 other schematics (and a VCR), and sure enough, the values on the DE board appear to be wrong. muhaaahahaa.

#59 6 years ago

Well..... here's what I have.

First I read the schematic and was thrown off. I read it that the 4 parallel capacitors were 4700uF 25V - which were way off. This should be 15000uF. So I put in another 10000uF and did some measurements.

1) without. I had 11.3V with 300mV AC ripple on the 12V. The voltage is low and the ripple is too high.

2) with added caps: My regulated voltage **dropped** to 11.2V but the ripple also dropped (as expected) to 150mV. The hum also was noticeably lower - but still present. I expected the DC voltage to increase though.

I was a little surprised at the lack of correction, then I looked at the values and each cap is 4700uF - so the total was almost 20kuF - which is more than enough for this rudimentary output. Looks like we have a design issue.

So, Matt - you are correct. This +12V output is the problem. I suspect that the original capacitors could be going bad (although I have a HUO Frankenstein with virgin boards). This can be solved by adding an external 12V regulator and bypass it entirely like you said. It would probably be easiest and still look mostly factory if you use a generic power supply. I will still probably replace the caps on this board anyway to see what happens... but my guess is that the sound board does not properly regulate and clean the unregulated +12v supply and expects a cleaner input.

this looks interesting

ebay.com link » Dc Buck Converter 10 15v To 0 9 12v 25w Step Down Voltage Power Supply Module

#63 6 years ago

it easily could as it doesnt really offer any details on how clean the power is. Although a cheap experiment.

#98 6 years ago

Not to sound redundant - but the issue is the power supply and nothing else.

Some supplies appear to exhibit less noise than others regardless of the newness of the caps and possibly bridge rectifier.

If you do not care about looks, you can easily drop in a 200W arcade power supply that will supply +12v and -12v (or PC power supply if you jumper the right connector to allow it to turn on without a button). They cost about $35 and should be good to go. Just connect the grounds together.

I'm personally out of interest now to try to solve or fix why the original power supply is deficient. It could be from overly noisy transformer or to various resonances in the circuit. Either way, we have a solution but not a fix at this time.

#110 6 years ago
Quoted from vid1900:

A few years ago I was playing a Russian mobster in a movie and there was a giant ground loop getting into both the audio feed (boom mic) and into the video (rolling bars).
We were loosing light, and although it's normal for lead actors to come back to overdub their lines, it is normally never done for a one line speaking part, as I had.
Everyone was in a panic so I stepped out of line and suggested to start unplugging things until we lost the ground loop.
It turns out it was the DAT (Digital Audio Tape) recorder for the boom; a very necessary part of the production.
We used a "cheater plug" on the DAT power cord that took a 3 prong grounded and turned it into a 2 prong ungrounded plug. This broke the ground loop and we finished the shot.
Now the same generator, lights, DAT, mixer and camera set up had been used together 100 times before, but on this occasion the DAT deck was somehow finding another path to ground and mucking up everything.
=
Another time a friend had installed a zillion dollar home theater set up and had a 5 channel dedicated amp to run 5 speakers. About a month into using it, just the front left speaker started humming loudly with 60hz hum.
He was blaming the amp manufacturer and swearing up a storm.
After swapping inputs I found that it would only hum when all 5 inputs were in use. Unplugging any of them killed the hum in the left speaker.
Lifting the Comcast feed cable from the rack instantly removed the hum, so we used an isolation transformer between Comcast and the rest of the equipment and all was well.
Somehow in the last month, Comcast had given itself a different ground potential and the symptoms showed themselves in just one channel of the amp.
Strange stuff these ground loops...

thats wacky. Good info though

1 week later
#126 6 years ago

Also newer DMDs don't buzz like what you're hearing. I had some perfect working ones that buzzed and new ones are silent

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