(Topic ID: 288950)

WPC 12738 Soundboard with blown tantalum caps.

By wrd1972

7 months ago


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  • 25 posts
  • 13 Pinsiders participating
  • Latest reply 6 months ago by Roamin
  • Topic is favorited by 1 Pinsider

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    Wpc_pre-dcs_tantalum-cap-polarity (resized).jpg
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    #1 7 months ago

    I have a damaged WPC 12738 Soundboard to fix. It is totally dead with the following tantalum caps blown:
    c26
    c46
    c47

    No other visible damage.
    What's the likelihood that if I replace those three caps, the board might work correctly?

    Thanks

    #2 7 months ago

    You can try it. What sound board do you need? Dcs or reg WPC89

    #3 7 months ago
    Quoted from wrd1972:

    What's the likelihood that if I replace those three caps, the board might work correctly?

    If it was working prior to the caps blowing and there's no other visible damage, then it's more likely than not that replacing the caps could bring it back to life.

    However, if you have no history about the board, the caps are easy enough to replace as a starting point.

    #4 7 months ago

    They are WPC89 for BSD and DrWho.

    I have been calling around the various repair shops and everyone is backed up 2 months.

    #5 7 months ago
    Quoted from wrd1972:

    I have a damaged WPC 12738 Soundboard to fix. It is totally dead with the following tantalum caps blown:
    c26
    c46
    c47
    No other visible damage.
    What's the likelihood that if I replace those three caps, the board might work correctly?
    Thanks

    Start there, you may get the Bong sound back. May have blown the Amp

    #6 7 months ago
    Quoted from ForceFlow:

    If it was working prior to the caps blowing and there's no other visible damage, then it's more likely than not that replacing the caps could bring it back to life.
    However, if you have no history about the board, the caps are easy enough to replace as a starting point.

    ^ This ^
    Although tantalums are wonderful caps for stability and long life (yes, this IS true) - be aware that tantalums are notorious for catastrophic failures when the slightest negative voltage or excessive voltage is applied. If this happened, the bad tantalums could be just the tip of the iceburg.
    When replacing tantalums, I prefer to increase the voltage ratings up to the next voltage level.

    #7 7 months ago

    Interesting topic, seeing I just replaced that board with a Pinsound board and mine was original to my Dr Who. I am going to look at that board to see what my Caps look like. My original board was working fine, I just wanted to add custom tunes to my machine. Are we talking about the big black Caps at C13 and C25?
    DSCF1981 (resized).JPG Doesn't it look like C28 on my board looks a little toasty?

    #8 7 months ago

    Yes C28 looks burned.

    #10 7 months ago

    I have pretty much decided to send the boards off to ensure that any other issues are addressed. I don't have the equipment to deep diagnose. Also I am repairing other folks machines and I don't want it coming back because of additional issue that may pop up.

    Thanks for the input guys, Great discussion.

    #11 7 months ago

    ForceFlow - Thanks for this information and link. This explains why my original sound board worked but was not quite right. The Wiki even had a picture that was exactly like mine with a blown C28. WOW. No wonder the new sound board worked so much better. I can now remember when I would power up the original sound board, how I would hear a crackle sound coming from the speaker. But I could still hear the music and callouts. I have ordered 8 new caps 1UF at 50 volts, as prescribed by the wiki. It will be my experiment in board repair. LOL.

    1 week later
    #12 7 months ago

    My electronics order for 8 1uF axial tantalum capacitors using a 50v instead (original rating was 35V) for Caps at C26,C27,C28,C29,C37,C46,C47,C48 have arrived.

    Wpc_pre-dcs_tantalum-cap-polarity (resized).jpg
    #13 7 months ago
    Quoted from Tophervette:

    It will be my experiment in board repair.

    You picked a terrible board set to experiment on.

    I wish you good luck and am hoping for the best.

    #14 7 months ago
    Quoted from Pin_Guy:

    You picked a terrible board set to experiment on.
    I wish you good luck and am hoping for the best.

    Thanks. I don't need the board currently, as the Pinsound board is new and working way better than this 1992 mono technology. I could try and sell it for $250 as is or fixed for $300 as others have on this marketplace. So no loss really, if I royally screw it up. I did take several electronics courses in College and did electronics repair in the offshore oil industry in a previous life. I will attempt it and post a picture either way. Now, back to my restoration of the rest of the pinball machine. Ramps and posts on playfield are needing some love and installation.

    2 weeks later
    #15 6 months ago

    These Caps become more problematic as C 24 & C25 age and loss Capacity.
    You are on the right track with the Tant's. Just make sure you do the Electro Mains as well.

    The Audio Coupling Caps (47Uf) are also worth changing. This Sound Board is the Most difficult and labor intensive of them all.

    The 47 UF caps are 25 Volts sitting in 12 volt circuits so they haven't caused any problems yet but they will eventually.

    C26 C28 C47 C46 sit on the 25VDC unregulated supply lines...The other Tants are hanging off the 12 VDC regulated Supplies.
    So just change those 4 Caps..The other Tants will last forever

    #16 6 months ago

    I'm surprised nobody mentionned that both U4 and U3 might have been damaged by overvoltage , making the tantalum caps explode at the same time. I've seen this happen in the past and luckily simply changing the caps and regulators brought everything back to life. They are easy to test , even without any capacitors in place. You can test both +12 and -12 at J503. Pin 2 is ground Pin 3 is -12 , Pin 4 is +12 (Pin 1 is 5v).

    If you removed C26, you can use its positive leg to test for DC coming out of the bridge , the value might be weird a bit if C26 is missing , but you should get something around 30-40V. You can also measure the negative side of the bridge by measuring the voltage at capacitor C47 that was removed. With the red lead on the positive side of the capacitor , you would read negative voltage , again around 30-40 probably (might be a bit lower) .

    The +12v and -12v regulators might still be good , since the damage is on capacitors just before them.. I've seen it often where tantalum capacitors blow up , but damage doesn't spread much further..

    The regulators cost and the caps cost next to nothing. If these are the only issues (very likely) then this board can be repaired for under 10$.

    EDIT : I would change all 6 circled caps as they probably all have suffered damage, even if they some don't show.

    15.png
    #17 6 months ago

    Hi this is interesting would you guys always change these caps if you got hold of a machine from this era , what i am asking is if it works ok and they look ok would the techs amongst you change them anyways because of the age , do they (i think the term is dry out like electrolytic capacitors?)

    #18 6 months ago
    Quoted from willowpuss:

    Hi this is interesting would you guys always change these caps if you got hold of a machine from this era , what i am asking is if it works ok and they look ok would the techs amongst you change them anyways because of the age , do they (i think the term is dry out like electrolytic capacitors?)

    Yes, tantalums are effected by age just like electrolytics are. They are not as bad but could fail just like any other component. Older tantalums were more frail that today's and from what I read they often failed short, causing bigger issues. Changing those caps in the power circuit can never hurt. I don't think they are as critical as electrolytic, but if you have them on hand , change them it only takes a minute or two each and your board will have more chances of lasting another 25 years or more..

    1 week later
    #19 6 months ago
    Quoted from Roamin:

    They are not as bad but could fail just like any other component.

    When Tant caps go, though, they go up in a ball of fire. UNLIKE electrolytic caps do. They have started fires in the past. So yes, if I ever got a game with this board in it with caps that have NOT been replaced, I would, first thing.

    #20 6 months ago

    There's one thing that needs to be clarified "between" tantalum and electrolytic caps..

    Electrolytic and tantalum are not mutually exclusive terms.

    As is mentioned here:
    https://forum.allaboutcircuits.com/threads/what-is-the-difference-between-electrolytic-tantalum-capacitors.151736/#:~:text=Electrolytic%20capacitors%20made%20with%20aluminum,polarized%20form%20is%20more%20common.

    Just copying the text here for any future reference:
    ---------------------------------------------------
    Capacitors may be:

    polar or non-polar
    electrolytic or non-electrolytic
    aluminum or tantalum

    Ceramic, mica, mylar, polyethylene , polypropylene, aluminum, tantalum, etc. are materials used in the construction of the capacitor. Specifically, it refers to the dielectric material that separates the parallel plates of the capacitor. The material could be a solid, liquid or gas. A liquid electrolyte is often used and hence the term electrolytic capacitor.

    Electrolytic capacitors made with aluminum (or aluminium) are generally lower priced than those made with tantalum.
    Tantalum capacitors have higher capacitance per volume.
    Capacitors made with tantalum can be either polar and non-polar though the polarized form is more common.
    ---------------------------------------------------

    I replaced 4 tantalum caps on my preDMD WPC89 audio board with electrolytic 1uF/50V (same value) and they still work.

    #21 6 months ago

    Okay guys I replaced 3 blown t-caps on a WPC sound board that currently contains CFTBL ROMs. I installed this board with CFTBL ROMs in a Dr. Who and I am getting this at start-up:
    Bong - Bong - Pause- Bong.

    Also I am not getting any sounds at all but that could be due to the incorrect ROMs.

    Question. Does the Bong sequence above mean anything? And can I use mis-matched ROMs (for testing purposes only) on another WPC pin? Or must the ROMs be correct for the pin to get any sound at all?

    Thanks

    #22 6 months ago

    This is my experience. I tried a sound board from a Dr. Who with Dr. Who roms in an Addams Family and got no sound. Installed Addams rom in the Who board in Addams machine and sounds were correct. Ymmv.

    #23 6 months ago

    That Bong sound is the Boot.wav start up sound for a Doctor Who. Yes it comes from the ROM. Which to me (a novice), means that you are getting power to the board. Sounds from the ROM through the amp circuit all the way to a speaker. The music and callouts on the ROM are looking for specific triggers from boards, leaf switches and and chips that you are not using. Now an Addams Family and a Dr. Who share alot of similar boards and coding. So Pinball Postals post makes alot of sense.

    I have been trying my hand at replacing those caps. I got my blown one, C28, in and replaced with no trouble. I next went after, C26, C27 and C29, as they were all close together. I got C27 and C29 out no problem. Then I burned my finger on the soldering iron and gave up.

    #24 6 months ago

    Tantalum Caps will only fail if they are operating close to their Voltage rating. Every time I replace caps I up the Voltage rating if the Board Space is available.
    Install 50 volts Tantalum Caps. If you use a higher voltage rating Electrolytic they will last longer. I use 15,000 UF 50 volt caps on the Driver board. They are big but they fit with ease

    #25 6 months ago
    Quoted from wrd1972:

    Okay guys I replaced 3 blown t-caps on a WPC sound board that currently contains CFTBL ROMs. I installed this board with CFTBL ROMs in a Dr. Who and I am getting this at start-up:
    Bong - Bong - Pause- Bong.
    Also I am not getting any sounds at all but that could be due to the incorrect ROMs.
    Question. Does the Bong sequence above mean anything? And can I use mis-matched ROMs (for testing purposes only) on another WPC pin? Or must the ROMs be correct for the pin to get any sound at all?
    Thanks

    Not sure about the pause between your bongs , but 2 bongs would mean U9 , RAM 2064 fails and 3 bongs would mean U18 (Audio ROM) fails. You've changed the caps , but have you measured the voltages on board to see if all is OK ? If you pull out U18, U15 and U14 (if it's used) and power on , do you get the same bong sequence ? If you use audio roms from another machine, do you have the same symptoms ? Same bongs and still no sound ? If so , I would start to blame U9 that very well can have been damaged when your caps blew up (usually they blow up because of overvoltage) after all , C46 did blow up and it's on the 5V line, which powers all RAM / ROMS.

    1 - No issues...enjoy a game.
    2 - U9 RAM failure.
    3 - U18 ROM failure.
    4 - U15 ROM failure.
    5 - U14 ROM failure.

    EDIT : I imagine the pause could mean that you have error 2 AND 3 one after the other.. So both RAM and ROM might have died.

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