So I noticed yesterday that the music and sound fx got really strange sounding on my BG. Eventually it just locked on making a low hum through the subwoofer and that was it. I turned it off and back on and the sound came back on but sounded glitchy. I reseated the roms and pushed on some of the connections. The sound came back and was working fine for a few games and than went out again completely. Any ideas what some things are to check for this. The red LED on the sound board is flashing so I assume it's getting the right voltage.

seems to only do it when the game has been on for a little while. When it is first turned on, it works ok.

Seems to be some kind of heat issue

nobody has anything that they could suggest?

Here is what it does when it gets messed up. Sometimes the red light stays lit constantly sometimes the red light goes out completely.

I did try reading the repair guides to figure it out. I must be doing something wrong because when I check for dc voltage at the connector it doesn't read anything and it makes the game play a strange sound effect.

Actually I think the bridge rectifiers are in the cabinet under the playfield

How do I test the voltage on these? Isn't there more than two legs on the bridge rectifier? Which ones should I test Where are the smoothing caps located and is there a way to test them?

I did the following to try and fix the issues so far. Replaced the ribbon cable that goes to the auxillary sound board. Repined the power supply connector the one that gives off 5 volts on top I think it ends in J-2. I also repinned the connector that goes directly to the sound board. I used trifuricon connectors. I also reflowed solder on the header pins on the sound board and also on the auxillary power supply.

I want to test the BR and caps that you mentioned. Can you tell me exactly how to test these? The meter should be on DC volts and 20 right (20 is as low as my meter goes without going to Milli)

ok I took a stab at this not sure if I did it right or not as i couldnt find much on testing these things.

I put my meter on diode test. There is three Bridge rectifiers with four prongs sticking out of them. When you stand to the left of the playfield looking down in you can see a positive symbol on the right side and a negative symbol on the prong closest to you

+
(prong pos)
IBRI <-Prong not labeled (prong opposite of this one is not labeled as well)

/\
-prong negative

Please reference my poor diagram to maybe understand what I mean.

BR #1
When the positive terminal is on the + and negative on the - : reads 826
When I swap these two and put the + on the - terminal and vice versa: reads 622

BR #2
+ terminal on pos. and - terminal on neg. : reads nothing
Swapped : 538

BR #3
+ on posiive and - on neg. : nothing
Swapped : 1199

When I tested the prongs that are not labeled they all read out 2 no matter if I swapped the terminals or not. I did not run a lead from the positive or negative to any of the non labeled wires. I just tested the positive to negative than swapped neg. to pos. And I also tested the two unlabeled prongs together and swapped leads and tested them again

Hope this can be of some help.

can anyone tell me if any BR is bad? Please before tomorrow. I am gonna be ordering a bunch of stuff from pinball life and it would be cool if I needed to add a BR to the list that way I didn't have to pay shipping twice. I see the one reading looks high. Not sure if that is normal. Also one of them reads out when I test pos. to the pos and neg to the neg. The other two didn't Please let me know if you can before tomorrow morning that way I know whether to order a new BR or not. Thanks guys.

Sorry, I missed your update....
» YouTube video
If you read something by reversing the leads, then it's bad. However, it's kind of iffy if you tested it in circuit. In otherwords, best way to test it is with it disconnected.
Another way to test is with the game on. The BR has four markings. Usually +, -, AC and AC or ~ and ~.
With your meter on DCV, put red lead on + and black lead on -. You should read a DC voltage. The value should be in your schematics. If you don't have schematics, just report your measurements here and we'll go from there.
With your meter on ACV, put red lead on either AC/~ and black lead on the other AC/~. You should read an AC voltage. Post results here.
Let me dig up schematics while you're doing that and see what values you should read.

ok, a couple quick questions. will these bridge rectifiers be a good replacement for mine? http://www.pinballlife.com/index.php?p=product&id=411&parent=20 I want to know what kind I need to get so I can order some if they are bad. When I do these tests the game should be on right? I am having a hard time finding anything helpful in my manual. It doesnt tell you what size BR I need . I have found this in my manual. Tell me if this is what you are looking for? Thanks for helping me.

bridge_rectifier.png

There is a large cap located to the left of the BR. Looks like it was probably replaced once before. Anyway to test it? I don't have an esr meter to test in circuit.

pm me your email I will send you the manual if you want, that way you have the entire thing

so I want to lay both the red probe and ground probe across both legs of the cap so each probe touches both legs (kinda like I am trying to short it out) and measure it like that

I'm gonna go down and test them now. I will make a quick video that way you can see the tests in action and make sure I did everything right.

ok, good thing I asked first lol.

I emailed you the manual I am going down to do the tests now

I am uploading the video now. I accidentally had the meter set on the wrong thing when I tested the positive and negative prongs. So when I first went through it was wrong. You can see me change it to the correct setting when and I go back through and test it again. Videos about half way done uploading. Also I had to wait for the sound to get messed up before I did the tests. I figured that way it would give the best results

ok here it is.

I will check out RGP, never heard of it before. Yea I know. The guy that did my board repair told me its rare to see a system 80 b game working cause they have so many issues mainly due to connectors I hear. I did have the ground mods done so that is taken care of.

give it a minute or two, its fresh off the iphone and youtube has to process it. Should work now. Like I said ignore the beginning when I had the meter set on the wrong thing. I got a/c d/c switched around. Sorry I was reading your instructions and than following them to do the tests. Thats why there is so many pauses. Hopefully it is good enough for you to see the readings

Here is the readings from the video

meter on dc volts testing the positive and negative posts.

front shows 6.6
middle 24.7
rear one shows 12.1

change meter to a/c volts and testing the squiggly lines
front shows 8.4
middle shows 28
rear shows 10.9

capacitor shows 25.1

i do know for sure if I turn the game on and start a game and just let it sit there playing music and doing nothing else it will still mess up and the red led goes out and stays out or stays permanently lit. sometimes when I let the game sit for awhile and turn it back on it still doesn't work. I have to let it sit for like an hour for it to work again.

No problem I really appreciate your help. You have taught me how to test some things that I never knew how to and you showed me that atleast the BR are still good. One step at a time I guess with this old girl. I will post a message on RGP and see what happens. Thanks again greatly for helping me with this.

Just wanted to update everyone that John Robertson fr rgparchives and robertmee helped helped me figure out the issue. Turns out it was a bad ic chip on the sound board. Found that out by spraying freeze spray on all the chips and rebooting the game. When I got to the bad chip and sprayed it, the sound started working again. Thanks again guys for the help.

I messed up big time. I went to replace the chip that I just got today in the mail. I had a brain fart and removed the wrong chip ( and when I said removed I meant cut out and basically destroyed) The chip says T74LS374B1 on it and is located in A3 spot. I tried search great plains and other places for this chip. Did i just ruin my sound board?? I guess I leaned my lesson though