(Topic ID: 253919)

Help. Strange power supply problem AS2518-49


By Starmag

3 months ago



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  • 41 posts
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  • Latest reply 46 days ago by mbwalker
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#1 3 months ago

Hello,

I just got a non-working Space Invaders. I turned it on and checked for voltages everywhere. All the boards have +4.1, so I moved to the power supply. this is what I found:

TP1 +7.67 (Supposed to be 6.5 on -49 board) controlled lamps
TP2 +205 (+230VDC) displays
TP3 +9.91 (+11.9VDC for +5) for boards
TP4 +6.1ac (+7.3VAC) gen ill
TP5 +44.3 (+43VDC) solenoids

I'm aware that low voltages (4.1) at the boards can be caused by a bad power regulator on the SDB, but given that it's only being fed 9.9 instead of 11.9 (TP3), I think that may be the issue. I've heard that if TP4 is out of spec, and it is, that the transformer may be bad. The odd thing is, When I tested the F6 fuse holder for 115, I found out that with J1 and J3 disconnected and the fuse in, which is the correct 3A slo that doesn't blow, that I can't find a voltage on either side of F6 fuse's holders, but if I take out the fuse I can suddenly measure 116.5 on one of the fuse holders. The other fuse holder traces to a J2 blue wire that goes to the power switch. Interestingly, with the F6 fuse out, the voltages at the transformer return to normal. 7.3 for instance for TP4. I've verified with online pictures that the J2 connector wiring and the wiring to the back of the power supply board (as2518-49), is correct.

Shorted transformer or power switch? Where does the 116.5 go?

Any suggestions would be greatly appreciated.

#2 3 months ago

Welcome.
The transformers in these games are tanks.

Quoted from Starmag:

Interestingly, with the F6 fuse out, the voltages at the transformer return to normal. 7.3 for instance for TP4.

With the mains fuse removed, how are you managing to power on the game and measure correct voltages?

Quoted from Starmag:

TP3 +9.91 (+11.9VDC for +5) for boards

Measure the AC voltage across points E11 and E12 on the rectifier board (one meter lead on E11, the other meter lead on E12). How much AC voltage do you measure? It should be about 12 volts AC. This then goes into the BR2 bridge rectifier to be converted to the 11.9V DC.

When you measured that 9.91V on the rectifier board, was the solenoid driver board connected?

#3 3 months ago

There is only markings left for E10, can't discern the rest.

Yes, the SDB was connected, I just tried again with it disconnected and it's still 9.9.

I'm beginning to think I should just buy a PDB, mine's pretty hacked and they are only $60, and go from there.

#4 3 months ago
Quoted from Starmag:

There is only markings left for E10, can't discern the rest.
Yes, the SDB was connected, I just tried again with it disconnected and it's still 9.9.
I'm beginning to think I should just buy a PDB, mine's pretty hacked and they are only $60, and go from there.

Since the 12v does not increase with the driver board connected the C23 filter cap is bad or there is an open circuit between the rectifier board and the driver board for the 12v. The ground return for the filter cap is isolated with a single orange wire between the rectifier backbox plug and the driver board top right connector. Its common for this wire to burn up at either end.

Check voltage across the leads big c23 filter capacitor on the driver board. If it reads 9vdc there replace the cap. If it reads 0v or really low volts there the connectors are bad.

Consider doing the ground mods to the driver board. Should be shown in pinwiki and a few other places. Basically tie together all the grounds on the driver board instead of isolating some back to the rectifier board through connectors.

#5 3 months ago
Quoted from Starmag:

There is only markings left for E10, can't discern the rest.

E11 goes to the trace connecting to the bottom of the F3 fuse. E12 goes to the trace at the top right pin of bridge BR2.

Quoted from Starmag:

Yes, the SDB was connected, I just tried again with it disconnected and it's still 9.9.

See what barakandl said about capacitor C23.

Quoted from Starmag:

I'm beginning to think I should just buy a PDB

Sorry, what's a PDB?

#6 3 months ago

Sorry, Power Driver Board, I should have said rectifier board or power supply board.

I have to go to work, but I will try your suggestions later, and update the thread.

Thank you.

2 weeks later
#7 78 days ago

If anyone is still there, I finally got a new rectifier board and installed it. Before I had 9.9 volts where I should have had 11.9 TP3, whether or not I had J3 (backbox) plugged in. Now I have 11.7 with J1 and J3 unplugged, 9.9 plugged in. I still have 4.1 at the boards. 9.9 at the SDB connector, 9.9 at C23.

I'm going to try changing the original C23 cap on the SDB next and check for cold solders, plus make some ground mods. Any suggestions would be appreciated.

with just J2 plugged in at the rectifier I get:
TP1 7.6 (should be 6.5)
TP2 150 (should be 230, I have 188 at displays)
TP3 11.7
TP4 7.3ac
TP5 44.5

#8 78 days ago

First, with the machine off:
Disconnect the J4 connector from the MPU board
Disconnect the J1 connector from the sound board.
Both these connectors carry the 11.9V to these boards.

Power on. Does TP3 on the rectifier board now measure 11.9V again?

If not, with power off, disconnect capacitor C23 on the solenoid driver board, then power on and remeasure.
If the voltage now returns to 11.9V, then C23 is suspect.
If not, you might be looking at a faulty 5V regulator on the solenoid driver board or something downstream from it that's overloading the regulator.

#9 78 days ago

Thank you Quench, your suggestions are super helpful and appreciated. This something I haven't come across before.

1 week later
#10 69 days ago

Here's an update.

A friend sold me a good SDB for $40, so I'm not repairing the original for now. I now have a solid 5.1vdc at all the boards. Yay. I removed the crusty battery and cleaned up the crusty MPU and rebuilt the crusty J4 connector and.... game up! My next problem is that I only have sound when the game is cold. Yesterday it was 75 out in the garage and I only got sound for a couple minutes. Today it's 60 this morning and I got sound for maybe 15 min before it went to silence. As far as I can tell, the board is all original and has never been worked on. One of the caps right above the connector is bulging. I plan on replacing all the caps. Any other suggestions?

Also, I have a display out, I've swapped it and it's that display. It has a character that looks like a "F" with no top segment for every digit. I've reflowed the pins. Action offers a kit with a bunch of resistors, transistors and a decoder chip and socket for $10. I'm thinking I'll try that first. If it doesn't work, any suggestions for a Pinsider that repairs displays reasonably with a decent turn around time?

#11 69 days ago
Quoted from Starmag:

One of the caps right above the connector is bulging.

You mean capacitor C13? It's probably not going to be causing your sound cutting out problem but if it's bad, it's very likely its brother of same value at C5 is bad and that one interfaces sound from the pre-amp to the output amplifier. Replace all the electrolytics and see how you go.
Another thing, since the problem is thermal, you can use freeze spray (or air duster in a can which expels refrigerant) to cool components to isolate the problem.

Quoted from Starmag:

Also, I have a display out, I've swapped it and it's that display. It has a character that looks like a "F" with no top segment for every digit.

It's probably the 4543 BCD decoder chip on the display board. It's responsible for generating the numeric characters. To display a "F" like character with no top segment for every digit would otherwise require failure of many other components. Suspect the decoder chip first.

#12 69 days ago

Thanks Quench. Yes, C13. Freeze spray is a great suggestion if the caps swap doesn't do the trick. I've ordered all the parts already for both. I'll replace the decoder chip first on the display before I go further.

Many thanks again,

Starmag

2 weeks later
#13 52 days ago

Another update. My friend's SDB failed so I put a 5V repair kit in my original and it's working great.

The display problem was fixed with a decoder chip and socket.

The sound works fine at start up but goes quiet after one game or so. It lasts a bit longer when it's colder in the garage, so I guess the problem is thermal. I have replaced all the caps. the 3 right side of the 5 chips that are socketed on the sound board feel pretty warm. I tried cooling them off with compressed air, but the sound doesn't come back until the game is shut off quite a while. I don't have test eq. so I was thinking I might shotgun a couple of chips in there before I just give in and buy a new one from barakandl. Based on the symptoms, which chips should I throw in there first? U2? Which I believe is a PIA 6821. Which one has the game code?

#14 52 days ago

Does the sound go quiet instantly or does it fade to quiet over seconds/minutes? If it's slowly you're looking at an issue in the amplifier section.

Have you freeze sprayed U8 (mixer/pre-amp) and U9 (output amplifier) - in terms of chips, they're the first suspects.

When it's gone quiet, what voltages do you measure on the outputs of the amplifiers? The schematic says output pin 4 of U8 should be around 2.2 volts and the output pin 4 of U9 should be around 6 volts.

Also check the voltage at TP1 on the sound board which should be around 13 - 14 volts.

#15 52 days ago

The sound just cuts off completely. Occasionally it will then come back on, but then only for a few more seconds, then cuts off and stays off until the game cools off again.

I'll be trying your suggestions tomorrow.

Thank you for your time, you are the best Quench.

Starmag

#16 52 days ago

U8 and U9 test out good. When the sound goes out it does so instantly, it doesn't fade away, and when the game sounds stop there is still hum which goes up and down with the volume pot. That hum changes with the display change from "last game" to "high score". So it appears that the amp section is good. Zero sound when playing a game, not even hum. The sound is fine for the first game or so.

#17 52 days ago

Also, I have re-seated U1-4 and U10. Temp wise U3 is hottest, U4 a little less and U10 a little less than U4, but still much warmer than U1 or U2. I tried cooling these down with compressed air which made them quite cool to the touch, but cooling them didn't bring the sound back.

#18 51 days ago

When the sound has died, what happens when you press the red test button on the sound board? Does it play any sound effects?

#19 51 days ago
Quoted from Starmag:

Also, I have re-seated U1-4 and U10. Temp wise U3 is hottest, U4 a little less and U10 a little less than U4, but still much warmer than U1 or U2. I tried cooling these down with compressed air which made them quite cool to the touch, but cooling them didn't bring the sound back.

if the CPU jumped out of program and crashed from overheating it would need rebooted before sounds come back.

If you get major hum/noise from the display coming out the speakers its usually a connector problem at the sound board. I think that happens when the 12v isolated ground return opens up. Its an end pin on the connector and likes to crack. Check the connectors.

#20 51 days ago

Quench: Amazingly, I haven't tried that. I'll let you know. I don't even know what it's supposed to do. I suppose I can try it at start-up and compare that with what it does after the sound goes out. Or look up it's function in the manual online.

Barakandl: "if the CPU jumped out of program and crashed from overheating it would need rebooted before sounds come back."

Of course, completely sensible, that's probably why I haven't tried that. lol. I will cool one chip at a time, then re boot and maybe I can pinpoint it the problem component that way. Great observation.

The hum I get isn't major, just lightly audible. After reading many other posts, it seems normal for this series of games. I just mentioned it to reference that it appears the amp section is working even after the game sounds cut out. I have re flowed the pins, but I will check the connector again.

I understand that there is four lines of info that are sent to the sound board from the MPU. Could this problem originate on the MPU and what chip would that be? I would try cooling that as well.

I don't yet have the advantage of using the diagnostics in the game because the red test button on the coin door is also non functional! The switch works, and I've tried crossing the wires, still no dice. I haven't yet checked the continuity of the wires. Then MPU I would imagine. That's next on my to do list. I may have to fix that first. We'll see. I have had to fix every board in this game. The varistor is a nice shade of charcoal black, so the game has suffered lightning or a major power surge. I am getting closer though, thanks to you guys and your excellent suggestions. Just the sound and test button left to do on a game that was very,very broken, but very very clean, so it's worth the effort.

#21 51 days ago

For Future Spa and Nitro I don't think they programmed the test button to do anything except maybe crash the software and cause you to need to reboot.

The sound board shares the momentary solenoid signals (SOL-A B C & D) and maybe one signal from MPU J1 P7 (SOL-E or digit drive 7 in million scoring games). The SOL BANK SELECT low enables the solenoid driver board to use these signals and when high enables the sound board. If there was a problem with this signal solenoids would fire when sound would play.

If there was a problem with the solenoid signals the solenoid board would most likely be firing solenoids out of order unless there is a connector issue at the sound board, sound board 4049 is bad, sound board AY-3-8910 is bad. Since the board works intermittently, the 4049 and sound chip is probably OK as those chips almost never fail intermittently, if they are bad, they are bad always.

#22 51 days ago
Quoted from Starmag:

...I tried cooling these down with compressed air which made them quite cool to the touch, but cooling them didn't bring the sound back.

I'd get a can a freeze spray for electronics before shotgunning it. If it really is thermal (i.e. stops working when warm), you should be able to spot it fairly quickly. You can also use a piece of paper, etc. to help shield individual components when you spray. Helps to narrow down the specific part.
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#23 51 days ago

Update. The test switch on the sound board does nothing after the sound quits. I forgot to try it at start up. the game is cooling off now so I'll try again when I have sound.

Cooling the chips to a very cool to the touch state with compressed air does nothing, even after a re boot.

I did however think of testing continuity between pin 1 and the rest of the pins on that chip and this is what I found:

with the game off

on the sound board:
U1 pin 1 has continuity with 3 other legs
U3 2
U10 2

on the MPU:
U9 4

all of which are socketed for easy replacement. I'm thinking I should I just replace those and go from there. Thoughts?

All other chips in the whole game pin 1 has no continuity with any of the other legs on that chip.

#24 51 days ago
Quoted from Starmag:

...Thoughts?...

Get some freeze spray, really!

It could also be a bad solder joint. After it is acting up, give the board a little bit of a press in several areas. If the sound comes back, then start looking for a cracked solder joint, broken trace, etc. Might be hard to spot, to the point of being easier to just touch up a bunch of solder connections.

#25 51 days ago

I'm cheap but not too cheap to get a can of freeze spray, if I think I have to. lol. I just don't think I should have continuity on those chips though. I will wait for a learned response on that.

I have already done the rest of your suggestions with no result. I don't think at this point it's a solder or socket issue. I've looked at it with a magnifying glass and other than the caps I put in and pins I re soldered, it's never been touched and very very clean.

#26 49 days ago

Well it appears I was wrong and you were right mbwalker. Even though I haven't bought some freeze spray yet, I can bring the sound back by isolating U8 LM3900n with a tube of cardboard and blowing compressed air on it for 30 secs. I had just tried it previously with the larger chips above it. Thanks.

#27 48 days ago
Quoted from Starmag:

Well it appears I was wrong and you were right mbwalker. Even though I haven't bought some freeze spray yet, I can bring the sound back by isolating U8 LM3900n with a tube of cardboard and blowing compressed air on it for 30 secs. I had just tried it previously with the larger chips above it. Thanks.

Nah, you didn't say/do anything wrong. I'm just an old fart that has used freeze spray sporadically over the years. And chasing down a thermal problem is a little harder with air than freeze spray. Freeze spray REALLY gets cold instantly. Like frosty cold! Good deal w/the cardboard tube for isolation.

Just make sure you didn't cool any possible culprit right next to the audio chip. Try cooling down parts next to the audio IC, excluding the audio chip to be sure.

Sounds like you are on the right track tho!

Also, does the audio chip have a heatsink with thermal grease? It the thermal path used to cool the IC is so-so (loose heatsink, dried out thermal grease), that can cause the problem too. The IC might just be going into thermal shutdown.

#28 48 days ago

I was not able to isolate the resistor right above it, (it's too close), however I figured that some extra fresh solder on U8 couldn't hurt anything even though the factory solders looked fine , even with a high power magnifying glass. I figured the fresh solder would actually make it easier to remove if I had to. The sound has not cut out again but we've had a bit of a cold front come in and it's fairly cool in the garage, so I'm not sure yet that it is permanently fixed yet, but I know I'm closer. I tried cooling the IC to no avail. If it isn't the LM3900n, it must be that resistor above it. Before I resoldered U8, no matter how cool the garage was, the sound would cut out after a few games and now I haven't lost the sound yet. Fingers double crossed. Thank you for the suggestions.

#29 48 days ago

I just looked up the LM3900..that's just a quad op-amp. I was thinking it was the output audio amplifier. So obviously my heatsink question is a 'whoops, nevermind'. LOL.

What pin is this in?

#30 47 days ago

Space Invaders. Unbelievably clean but unbelievably broken. I've had to fix literally every electronic device in it. The varistor was crispy black, so it suffered a bad power surge at some point.

Even though I'm not sure the audio is permanently fixed yet, I hooked up a Klipsch 12" downfiring subwoofer to it I keep for workshop games. It makes those low end sounds it makes amazing. I had to put the sub on a piece of carpet to keep it from dancing across the floor. lol.

If the audio is fixed, I'm down to one problem. The test button on the door doesn't work and the switch is good. I've tried crossing the leads to no avail. I'll check the wires end to end. One seems to go to the SDB and one to the MPU. I'm thinking the MPU at this point because it had some acid damage. The lower left MPU connector needed to be rebuilt so maybe the lower right does as well. That's where the red from the door test switch goes.

I am close to victory, which I always celebrate with a shot of JD. I can almost taste that spicy oak barrel now.

#31 47 days ago

Sorry, I should have asked the last time...Is there a Ux by the chip? Like U1 or something similar? I'll look up the schematic and take a peek at the circuit.

#32 47 days ago

Yes, U8! I'm really sure I had it isolated when I cooled it though.Also isn't the heat sinked transistor the output amp? It was still working when the game sounds would die. You could turn up and down the usual display hum with the volume on the sound board.

#33 47 days ago
Quoted from Starmag:

Yes, U8! I'm really sure I had it isolated when I cooled it though.Also isn't the heat sinked transistor the output amp? It was still working when the game sounds would die. You could turn up and down the usual display hum with the volume on the sound board.

Yeah - the heatsunk transistor is probably the actual output device that drives the speakers (haven't looked at the schematic yet, was just looking it up). I was thinking the LM3900 was the output amplifier, until I looked it up and saw it was just a lower level audio amp - my mistake.

#34 47 days ago
Quoted from Starmag:

Also isn't the heat sinked transistor the output amp?

Yes, U9 on the heatsink is a TDA2002 which is an audio output amplifier.

#35 47 days ago

OK, looked up the circuit.

Not much going on there. I doubt R5 is bad. R4 - the same. Not impossible, but unlikely. C3, the 68pF cap - I'd blame that before the resistors - but I'd blame U8 first.

The schematic shows a couple of voltage levels you can check when it acts up.
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#36 47 days ago

Wow, thanks for digging that up. I just saved it .

#37 47 days ago

Link: https://www.ipdb.org/search.pl?any=space+invaders&search=Search+Database&searchtype=quick

Scroll down a ways to the Space Invaders by Bally section, the look a little bit lower to Documentation. Full schematics there.

#38 47 days ago

C3 is new. I replaced all the caps.

#39 47 days ago

U8 is up next then. I should have the resistors if you want to replace just for the heck of it... Just PM me your address.

#40 47 days ago

I will if I need it. Thank you for the kind offer.

#41 46 days ago
Quoted from Starmag:

I will if I need it. Thank you for the kind offer.

NP, it's just the cost of a stamp...

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