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(Topic ID: 263807)

Blowing F501 and F502 on Boot No Sound


By PinballGurus

7 months ago



Topic Stats

  • 54 posts
  • 7 Pinsiders participating
  • Latest reply 6 months ago by eyeamred2u
  • Topic is favorited by 1 Pinsider

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There are 54 posts in this topic. You are on page 1 of 2.
#1 7 months ago

Can someone point me in the right direction on this please?

My Dr. Who is blowing the F501 and F502 fuses whenever I boot the machine. It has a blown trace on the back of the sound board and a few blown capacitors I repaired, but it is still blowing the fuses. Not sure if the problem is the sound board itself or something else.

Thanks in advance.

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#2 7 months ago

Have you tested the four big diodes?

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

#3 7 months ago

Not sure if it matters but the trace looks like it is touching the fuse solder pad in picture 1.

#4 7 months ago

that trace is 20vac i think....the fact both fuses are blowing leads me to believe you have a big fat short in your power ckt. check those diodes! also check the regulator....

#5 7 months ago

Yes. Sorry. The diodes all tested good. First thing I checked.

Quoted from ChrisHibler:

Have you tested the four big diodes?

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

#6 7 months ago

I pulled the trace off. I was really hoping that was blowing the fuses, but nope.

Quoted from bssbllr:

Not sure if it matters but the trace looks like it is touching the fuse solder pad in picture 1.

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#7 7 months ago

Where do I test the voltages on this board for the 25v and -25v?

#8 7 months ago
Quoted from PinballGurus:

Yes. Sorry. The diodes all tested good. First thing I checked.

#9 7 months ago

All 4 diodes tested the same... good. What regulator?

Quoted from Startek2:

that trace is 20vac i think....the fact both fuses are blowing leads me to believe you have a big fat short in your power ckt. check those diodes! also check the regulator....

#10 7 months ago

Testing the amperage to the fuse shows .07 amps, which shouldn’t be blowing the fuses, right? Unless I’m doing the test wrong or missing something. All my test LEDs are correct.

#11 7 months ago

Replaced the blown capacitors.
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#12 7 months ago

Perhaps I’m testing the amperage wrong?

#13 7 months ago

Overall the machine seems to work, except the sound board.

#15 7 months ago

I noticed someone placed a wire in the center battery because the contact broke; terrible repair. Before I noticed it I replaced the batteries; as they were bad and I think I shorted out the middle battery (see photos) as it got hot and expanded (photos). So I repaired the “wire” bs and replaced the batteries. At some point I noticed the sound dying, but it was too late. My assumption is the middle battery short caused the blown sound board trace... After fixing box the battery issue and the sound board issues (capacitors and trace) the sound board is still blowing both F501 and F502 fuses upon startup. Ideas appreciated. I’m reluctant to just buy a new sound board if their are other issues, but all the LEDs and TP are correct. Ideas?

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#16 7 months ago

There is a loud buzzing coming from the DMD.

#18 7 months ago
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#19 7 months ago

get that battery off that board! run a wire to a BATTERY PACK or install an NVram!

#20 7 months ago

I’m going to order a bunch of NVRAMS soon. Any favorite spots to get them?

#21 7 months ago

Until then I want to fix my sound board.

Can’t wait to try this game.

#22 7 months ago

Would I be correct to assume the issue lies on the audio board and not another board?

#23 7 months ago

So I decided to try and unplug the main speaker and the fuses stopped blowing. When I replaced the speaker (was blown) and plugged back in the speaker wires the speaker makes a loud buzzing/humming sound and the speaker pulls in; which ostensibly blew the other speaker to begin with. Not sure what part of the board to tackle next... likely a bad amp?

#25 7 months ago

I read this... but now I’m starting to wonder if the hum from the display and speakers are related?

Hum is typically from failing capacitors on the sound board power supply. ... If not the smoothing capacitors are failing. This puts AC on the amplifier rails, and causes the hum.

#27 7 months ago

Send your sound board out for repair. Send the MPU along with it to have NVRAM installed.

I can take care of both if you would like.

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

#28 7 months ago

Sending it for repair is the easy way. Why ask for help on a repair forum if I was someone who would just send the board off for repair? No thanks.

#29 7 months ago

So anyways... if you’re someone, like me, who doesn’t mind fixing their own boards here’s the list of things that will likely need repaired on the board if it’s doing what mine is.

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#30 7 months ago

Thanks for the link. I think I was looking at the wrong board; seems they tried a few soundboards in that era.

#31 7 months ago

I’m hoping my electronics store has the capacitors I need. Planning on C20 C22 C23 C46 today and reporting back.

#32 7 months ago

No worries...and thanks for posting the text of the sections I wrote for the PInWiki. I’m glad that people are finding those useful.

You surely wouldn’t be surprised by the number of people who ask for help but really don’t have the capability to use the information correctly.

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

#33 7 months ago

Very impressive that you wrote that. Someday I hope to be as good at you. I work repairing cable TV converters, etc. so this stuff is new to me, but not much different otherwise. If I can’t get it myself I’ll 100% send it to the expert.

Quoted from ChrisHibler:

No worries...and thanks for posting the text of the sections I wrote for the PInWiki. I’m glad that people are finding those useful.
You surely wouldn’t be surprised by the number of people who ask for help but really don’t have the capability to use the information correctly.

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

#34 7 months ago

So today I changed the C23, but my parts store only has a radial capacitor so I hope that’s ok? Anyways that didn’t do the trick. I have more capacitors to replace still, but I decided to check my speaker leads for voltage and they had about 8.8 volts going thru each. When I unplugged the ribbon cables I noticed the voltage went up higher too; around 15 volts or so, which I thought was strange, but whatever. I also checked for AC current on the two large capacitors and notice about .154 volts on the outer cap, while the other showed none.

Just hoping I’m not replacing all these caps for nothing. There’s got to be a better way to test capacitors other than pulling them out... no?

#35 7 months ago

Here’s the radial cap I used to replace C23.

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#36 7 months ago

Radial and Axial caps are functionally identical. They differ only in physical lead placement.
I looked back at the pics. C28, normally a tantalum cap, has been replaced with an electrolytic. That's fine.
What might not be fine is the carbon residue/burn that remains. Carbon is conductive. Use your ohm meter to see if the legs of that cap are shorted to adjacent parts via the carbon.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#37 7 months ago
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#38 7 months ago

Well I replaced C20 C22 C23 C46 C47 and have the exact same issue, so I guess I will replace the next series C26-C29, C37, C46, C47, and C48. Not sure where to go after that. Looks like the voltage regulators and then the amp chip???

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#39 7 months ago

Take a look at the schematic. It's on page 15 (sheet 2 of 2 for the Sound Board). If your fuse is blowing immediately without any trigger (i.e. pretty much when turning on the machine) then there's probably a direct short from the supply power to ground. You should probably measure to check there's a direct short and then test (or remove) components until you find the short. Shotgunning does work but it's not efficient.

You've check the diodes. If after you've had fun with the capacitors and you still have the short go for the ICs. That would be the LM7812 and LM7912 voltage regulators as well as the LM1875 amplifier.

#40 7 months ago

Personally I’m thinking the same but no idea where to start?

Quoted from DumbAss:

Take a look at the schematic. It's on page 15 (sheet 2 of 2 for the Sound Board). If your fuse is blowing immediately without any trigger (i.e. pretty much when turning on the machine) then there's probably a direct short from the supply power to ground. You should probably measure to check there's a direct short and then test (or remove) components until you find the short. Shotgunning does work but it's not efficient.
You've check the diodes. If after you've had fun with the capacitors and you still have the short go for the ICs. That would be the LM7812 and LM7912 voltage regulators as well as the LM1875 amplifier.

#41 7 months ago

The machine was only originally blowing the F501 and F502 fuses when the blown speaker was installed. After removing it the fuses are good unless I let the new speaker blow. There’s something adding voltage to both the display and the sound board IMO; hence the hum from the sound board... ideas?

#42 7 months ago

Which diodes specifically. I only checked the four main larger diodes.... bridge rectifier. Are there others I should be checking?

Quoted from DumbAss:

Take a look at the schematic. It's on page 15 (sheet 2 of 2 for the Sound Board). If your fuse is blowing immediately without any trigger (i.e. pretty much when turning on the machine) then there's probably a direct short from the supply power to ground. You should probably measure to check there's a direct short and then test (or remove) components until you find the short. Shotgunning does work but it's not efficient.
You've check the diodes. If after you've had fun with the capacitors and you still have the short go for the ICs. That would be the LM7812 and LM7912 voltage regulators as well as the LM1875 amplifier.

#43 7 months ago
Quoted from PinballGurus:

Which diodes specifically. I only checked the four main larger diodes.... bridge rectifier. Are there others I should be checking?

Quoted from DumbAss:

Take a look at the schematic. It's on page 15 (sheet 2 of 2 for the Sound Board).

If you don't know how to read a schematic you should say so. I don't know your knowledge level but I assume if you are de-soldering and replacing components on a printed circuit board you know how to read a schematic.

#44 7 months ago

Ok. So I have a dead short on pins 6 and 7 which carry 20 volts AC. I’m starting to figure this out. Thanks for your patience. I just was able to print the schematic.

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#45 7 months ago

It's ok to not know something. That's when you ask for help. If you're willing to read and learn I'm willing to point you in the next direction to the limit of my knowledge and experience.

Those pins should be tied together. Picture attached. Pins 1 and 2 connect to one end of the VCT from the transformer. Pins 4 and 5 carry the other end. Pins 6 and 7 connect to the center tap - which is why it is connected to the power ground.

Check the diodes (I believe you stated that you have already done this). Check the capacitors (unlikely but possible). Check the ICs. For the ICs you will need to know which pins connect to where. The schematic labels the pins for the amplifier but it does not label the pins for the voltage regulators. You can find data sheets to acquire this information.

j501.jpg
#46 7 months ago

So pin 6 and 7 should be ground on the board. Good to know. And everything seems in order otherwise. I’ll recheck my voltages and read more not that I have a good schematic and get back to you.

1 month later
#47 6 months ago

So I replaced the Amplifier chip and the board started working, but the sound eventually became more and more scratchy as the heat sink heated up. Ideas?

#49 6 months ago

I pulled my c26 and removed the carbon under it and replaced it. I also checked all the blue 47mf capacitors (all tested good), so I replaced the board and turned it on. Made a funny noise initially then beeped like normal the my c26 capacitor exploded. Not sure why?

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#50 6 months ago

That's a normal failure mode for tantalum capacitors. When they get old, they tend to explode. You SHOULD be good to just replace the cap and go on with life.
EDIT: Oh wait, now I see that it wasn't one of the tantalums that exploded... i guess you can disregard my advice, heh...

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There are 54 posts in this topic. You are on page 1 of 2.

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