(Topic ID: 289438)

Transistor Keeps Shorting

By Mando

3 years ago


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  • 43 posts
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  • Latest reply 3 years ago by Mando
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    #1 3 years ago

    So the transistor that corresponds to the drop ramp on my JackBot keeps shorting. Bought the game and it was shorted, had it replaced worked great for many many games. All the sudden ramp didn't drop again, sure enough fuse blown and Q48 shorted a TIP102.

    Brand new coil what could be causing this? And they would it work well for quite some time then fail again? If there was a short I would expect it to just blow again pretty quickly .

    #2 3 years ago

    You may have an open diode on the driver board that goes for that coil.
    Does the coil itself have one?

    If not wouldnt hurt to have one.

    #3 3 years ago

    Thanks coil has no diode . I can test what’s on the board ... will look it up as I don’t know how

    #4 3 years ago

    don't have the game but I would make sure there wasn't any other load on the circuit but the coil and if there is not I would probably check the (I call them anti-flyback diodes) across the coil is good and the right type. when the coil is de-energized you get a coil voltage spike in the opposite direction and if the diode is not there to give it a path to ground it can blow up the transistor

    #5 3 years ago

    Does the ramp work correctly mechanically? Is it showing anything weird in the switch test? If it's getting hung up or a switch is causing the coil to repeatedly fire to get it raise/lower could be the culprit.

    I'd check closely the lugs of the coil make sure nothing is shorting it out

    What those dudes said about diodes

    #6 3 years ago
    Quoted from CrazyLevi:

    Does the ramp work correctly mechanically? Is it showing anything weird in the switch test? If it's getting hung up or a switch is causing the coil to repeatedly fire to get it raise/lower could be the culprit.
    I'd check closely the lugs of the coil make sure nothing is shorting it out
    What those dudes said about diodes

    Ramps was working perfect we had dissambled and cleaned it . No switch errors so it knew it was closed .

    Trying to figure out how to properly test diodes .

    #7 3 years ago

    D19 reads .46 it’s a 1N4004 others read .56 .

    Not sure if that means much

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    #8 3 years ago
    Quoted from Mando:

    Ramps was working perfect we had dissambled and cleaned it . No switch errors so it knew it was closed .
    Trying to figure out how to properly test diodes .

    It wouldn't show a switch error if it were rapidly firing. It's worth checking it out in switch test to just to make sure. Takes 30 seconds. Always worth just ruling things out as you try to find a problem.

    Switch error reports don't always tell the whole story.

    #9 3 years ago

    Just tested switch works fine when ramp
    Drops and when up it’s off .

    #10 3 years ago

    Pretty sure diodes are fine they are between .4 and .6 in on direction only .

    #11 3 years ago

    .4 to .6 is typical forward biased (positive to anode ....arrow part) and negative to line side.........and should be infinity reverse biased positive to line side and negative to arrow however you have to pull one side up (unsolder it) off the coil to get a good reading

    #12 3 years ago

    The easiest and cheapest thing to do is replace the suspect diode. The diode test only supplies a small voltage and current to the diode.

    #13 3 years ago

    Thanks ... coil is actually partly de-soldered
    .

    I found the 5401 predriver seems to get a different resistance reading .5 in that circuit vs the other 2 above and below of 2.5 could that be the culprit ?

    I can replace all 3 (transistor , pre driver , diode) for good measure . Need to practice my soldering a little first

    #14 3 years ago
    Quoted from Mando:

    Thanks ... coil is actually partly de-soldered

    I found the 5401 predriver seems to get a different resistance reading .5 in that circuit vs the other 2 above and below of 2.5 could that be the culprit ?
    I can replace all 3 (transistor , pre driver , diode) for good measure . Need to practice my soldering a little first

    Because of your ongoing issues with this problem I would certainly replace all of those pre-driver parts as well as the diode across the coil.

    In situations like this I would also add an extra diode right at the coil terminals. It certainly can't hurt and it might just fix your problem. Band end of the diode faces the 50V side wire connection on the coil.

    Actually electronic design like this that puts the snubber diode on the PCB rather than right at the source of the back EMF is a very poor engineering effort. The long wires all the way from the coil to the PCB (where the diode is installed) actually act like antennas with the high voltage of the back EMF force - exactly mimicking Marconi's radio experiments. Poor engineering.

    #15 3 years ago

    Sounds good a 1N4004 ? (Or is 4007 a suitable replacement ?

    I can replace the TIP102
    1N4004 on the board
    5401 pre driver
    And put a diode on coil .. it’s this one although this is the “old” coil

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    #16 3 years ago

    The 1n400X family are all suitable as long as the number is higher than "4" - EG: 1N4004/5/7 are all perfect.

    You need to identify which side of the coil has the 50V supply wire connected to it so you know which way around to mount the diode.

    #17 3 years ago
    Quoted from pins4u:

    The 1n400X family are all suitable as long as the number is higher than "4" - EG: 1N4004/5/7 are all perfect.
    You need to identify which side of the coil has the 50V supply wire connected to it so you know which way around to mount the diode.

    Yeah I assume which ever wire is getting juice ?

    #18 3 years ago
    Quoted from Mando:

    Yeah I assume which ever wire is getting juice ?

    The difficulty is that, due to the very low resistance of the coil, BOTH sides of the coil will likely read very close to the same. Look in the manual to identify the wire colour that is the 50V supply, and confirm this by checking that this wire colour also connects to one side of most coils.

    #19 3 years ago

    I found a new coil that’s the same with the diode . Since I was ordering stuff added it can’t hurt . Other new one can be a spare

    #20 3 years ago
    Quoted from Mando:

    I found a new coil that’s the same with the diode . Since I was ordering stuff added it can’t hurt . Other new one can be a spare

    Great, you still to identify exactly which wire connects to which terminal. Don't guess this and don't accept that it will be wired to the same terminals as the original.

    1 week later
    #21 3 years ago

    Ok ... so I replaced Q48, q47 and D19 . Q48 shorted again ! So I tired the new coil ... made sure I knew which side with the diode was power ... and then proceeded to solder the wires wrong and not properly check my work I am an idiot .

    Anyhow it fried Q48, Q47, D19, r81 and R80 .

    I replaced all of those and the Diode on the coil ... soldered it correctly but now it does not fire . Every other coil is fine .

    When it circuit R80 does not seem to have the correct resistance find out of circuit .

    Only thing I have not replaced is R78 and R79 would have to order those . Anything else it could be ?

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    #22 3 years ago

    Thinking I have the wrong resistor a 68K not 68ohm lol. Would that do it ?

    #23 3 years ago

    If you installed a 68k instead of a 68 ohm , then definitely this won't work. 68 000 Vs 68 is a huge difference. Because the resistance is so high , it cannot properly close Q48. You need to use a value that is closer so it can generate the needed current at the base of the TIP102.

    You can mix resistors is series / parallel to obtain different resistor values.

    #24 3 years ago
    Quoted from Roamin:

    If you installed a 68k instead of a 68 ohm , then definitely this won't work. 68 000 Vs 68 is a huge difference. Because the resistance is so high , it cannot properly close Q48. You need to use a value that is closer so it can generate the needed current at the base of the TIP102.
    You can mix resistors is series / parallel to obtain different resistor values.

    Yes correct one will be here Tuesday . Hopefully after replacing basically every unit in this circuit will be back and running .

    I was so careful to make sure Find the hot wire then somehow I did it backwards and didn’t check lol .grrrrrrr had been too long a day I guess .

    #25 3 years ago
    Quoted from Mando:

    Yes correct one will be here Tuesday . Hopefully after replacing basically every unit in this circuit will be back and running .
    I was so careful to make sure Find the hot wire then somehow I did it backwards and didn’t check lol .grrrrrrr had been too long a day I guess .

    Sometimes it's best to sleep on it.

    #26 3 years ago
    Quoted from CrazyLevi:

    Sometimes it's best to sleep on it.

    CrazyLevi you are right you guys told me 100 times and I totally knew the Right way to do it ! Yet somehow I didn’t .

    Hopefully the board is ok looks fine and until my mishap was old but not played much .

    At this point on Tuesday I will have replaced every diode , transistor and resistor in the circuit . Wire seems ok , only thing I didn’t replace is the IC chip but all toner coils are fine .

    We shall see !

    #27 3 years ago

    Ok...so progress I got it all soldered back to "normal" I tested the drop ramp which is the problem transistor/coil with my multimeter.

    The good news is it doesn't seem to be locking on, and fires some voltage when tested.
    I do notice it always has a very very small amount of voltage on the line(less than one volt). Not sure if this is normal?

    I also notice that some flash lamps go off every time I fire a solenoid in test. They are all on J107 not sure if that indicated a short somewhere? I will post a pic below of which ones keep going off.

    Anyhow not hooking the coil back up just yet until I get some answers !

    #28 3 years ago
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    #29 3 years ago

    Lastly when I do hook it back up this is correct ? I am certain the red wire is the “hot”.

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    #30 3 years ago
    Quoted from Mando:

    Lastly when I do hook it back up this is correct ?

    Why do you have a diode on this coil?

    #31 3 years ago
    Quoted from GRUMPY:

    Why do you have a diode on this coil?

    Was suggested earlier in the thread as “extra protection “ can easily be gone

    #32 3 years ago
    Quoted from pins4u:

    Because of your ongoing issues with this problem I would certainly replace all of those pre-driver parts as well as the diode across the coil.
    In situations like this I would also add an extra diode right at the coil terminals. It certainly can't hurt and it might just fix your problem. Band end of the diode faces the 50V side wire connection on the coil.
    Actually electronic design like this that puts the snubber diode on the PCB rather than right at the source of the back EMF is a very poor engineering effort. The long wires all the way from the coil to the PCB (where the diode is installed) actually act like antennas with the high voltage of the back EMF force - exactly mimicking Marconi's radio experiments. Poor engineering.

    See this

    #33 3 years ago
    Quoted from Mando:

    “extra protection

    If you had 100 diodes, would this better? If one of the 100 diodes shorts, they all read as a short. So now you have 100 chances of a failure. Not better protection in my opinion.

    Use a better part for extra protection, replace the original diode (1n4004) with a 1n4007.

    #34 3 years ago
    Quoted from GRUMPY:

    If you had 100 diodes, would this better? If one of the 100 diodes shorts, they all read as a short. So now you have 100 chances of a failure. Not better protection in my opinion.
    Use a better part for extra protection, replace the original diode (1n4004) with a 1n4007.

    I did

    #35 3 years ago

    If you were to have replaced the diode, driver and predriver all together the first time you would be playing your game today. This has been discussed on PS for years, even recommended by myself since I joined.

    #36 3 years ago
    Quoted from GRUMPY:

    If you were to have replaced the diode, driver and predriver all together the first time you would be playing your game today. This has been discussed on PS for years, even recommended by myself since I joined.

    I did and it blew again ... but alas it’s working now and the flashers going off is only with LEDs? How long will it last ? I don’t know

    Every resistor , diode and transistor is new .

    #37 3 years ago

    Proof of life .. wish I was confident it will hold

    #38 3 years ago
    Quoted from Mando:

    I did and it blew again ..

    Maybe I miss read your post, but it seemed like you didn't replace the diode until you went thru a number of TIPs first.

    Glad it's working now.

    #39 3 years ago
    Quoted from GRUMPY:

    Maybe I miss read your post, but it seemed like you didn't replace the diode until you went thru a number of TIPs first.
    Glad it's working now.

    Well the “repair guy” just replaced the tip . It went again .. I replaced the TIP , Diode and pre-driver and it went immediately. Maybe I messed something up who knows . So I put a new TIP and then tried the dioded coil . In my haste I’d being bummed it failed
    The first try I had a brain fart and torched the entire circuit !!

    So I replaced every component in the circuit and this is where we stand .

    I will say I did find one flasher that was a weirdly close to touching some metal maybe somehow this was the cause but seems that would blow the flasher transistor . Never the less I moved that

    #40 3 years ago
    Quoted from Mando:

    Well the “repair guy” just replaced the tip . It went again .. I replaced the TIP , Diode and pre-driver and it went immediately. Maybe I messed something up who knows . So I put a new TIP and then tried the dioded coil . In my haste I’d being bummed it failed
    The first try I had a brain fart and torched the entire circuit !!
    So I replaced every component in the circuit and this is where we stand .
    I will say I did find one flasher that was a weirdly close to touching some metal maybe somehow this was the cause but seems that would blow the flasher transistor . Never the less I moved that

    It well could be a short like that.

    #41 3 years ago
    Quoted from CrazyLevi:

    It well could be a short like that.

    Time will tell ! I will say I got a lot of practice and lots of tools now

    #42 3 years ago

    I just saw this post and read through it, it was a fun read ... a few /facepalm moments but in the end its working and you probably learned a lot along the way.

    #43 3 years ago
    Quoted from Pin_Guy:

    I just saw this post and read through it, it was a fun read ... a few /facepalm moments but in the end its working and you probably learned a lot along the way.

    Only one way to learn ! Would have liked to not have done the backwards coil hook up but hey I will quadruple. Check from now on

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