(Topic ID: 165140)

CA3081 Replacements With Discreet Transistors

By barakandl

7 years ago


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  • 41 posts
  • 17 Pinsiders participating
  • Latest reply 1 year ago by pins4u
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    #1 7 years ago

    **** EDIT 08.22.16 ****

    It works. Considering selling these as a kit. You would get a sheet of blank PCBs, headers, and 2n4401 transistors.

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    **** Original post ****

    I pulled off a hack today. Dead transistor inside of the CA3081. I opened my part drawer and found I was out of the CA3081. To get the board going i decided to swap in a single 2n4401 transistor.

    All I did was snip off the bad associated CA3081 legs. Desolder the pads clean. Stuff collector and base into the appropriate pins of the CA3081. Emitter is all common together inside the CA3081 and attached to ground. Pin 5 and 15 of the CA3081 are grounded so you can use those, or like i did, just find a nearby ground pad that was most convenient.

    Then you don't have to replace the entire obsolete and expensive CA3081. Here is a pic of my hack fixing the q3 (its always q3 knocker circuit it seems) predriver for the CA3081

    20160727_125336_(resized).jpg20160727_125336_(resized).jpg

    Works on my test setup to light an LED. I will throw it in a real game tonight.

    That led me to also do this PCB layout with discreet NPN transistors.

    Untitled_(resized).pngUntitled_(resized).png

    I couldn't find a different transistor array to sub in, so i figure 2n4401 is probably acceptable commonly used discreet sub. I could make them available as a DIY kit. Any input is appreciated.

    #2 7 years ago

    This is what we're going to have to do for those Williams display chips...

    #3 7 years ago
    Quoted from cody_chunn:

    This is what we're going to have to do for those Williams display chips...

    Good idea... I think the 7180A is the most rare one we use. I will look into doing those too.

    #4 7 years ago

    Smart! It's guys like you that will keep these machines working.

    #5 7 years ago

    Got the size down as small as possible with zero extra vias. Might be too cozy for the transistors though.

    Untitled_(resized).pngUntitled_(resized).png

    #6 7 years ago

    Great Andrew!!!!

    See how we have it done about 10 years ago.

    CA3081-Adapter_(resized).JPGCA3081-Adapter_(resized).JPG

    #7 7 years ago

    What's the difference between CA3080 and CA3081? I've got lots of CA3080's from Synth repairs/builds. OTAs get used like crazy in a lot of them for VCOs, VCFs, & VCAs. But mostly LM13600/13700s get used these days in modern replicas because of the scarcity.

    Andrew, What about using LM13700s? There are still bazillions of them, especially in SOC form. The 13600 is unbuffered like the CA3080, so you'd just use 1/2 of it to replace a CA3080. But I think the 13600 is scarce. You can probably leave the diode bias unconnected on a 13700, ground the input and leave the output unconnected and you'll be in OTA business, unbuffered. I think.. Maybe. Never tried it as a direct replacement on a later Moog that used one or anything. I wanna breadboard one now and see if that works.

    But that would make for a neat little package, just hot air the SMD IC right onto a single layer board with headers.

    #8 7 years ago

    Love the idea of converting these over to discrete components. Great work!

    #9 7 years ago

    Great hack idea Andrew! I thought I needed one of the CA3081s earlier this week, thankfully it ended up being the 74LS138

    I bought a bulk lot of dead Williams Master Display driver boards from eBay and harvested the 7180s from them. I think I ended up with a lifetime supply!

    #10 7 years ago

    I think the other type of CA308X is for common collector instead of emitter.

    Ingo, tilting the transistors is perfect. My brain was stuck in right angles.

    DeFog, i have no idea what the LM13700 is. I will pull the data sheet and inspect. I was honestly surprised i couldn't find more transistor arrays in a small SMT package to use.

    I will play with the layout some more and decide what is realistic about transistor spacing and then order some. Should be really cheap once panelize the pcb layout.

    #11 7 years ago
    Quoted from barakandl:

    DeFog, i have no idea what the LM13700 is. I will pull the data sheet and inspect. I was honestly surprised i couldn't find more transistor arrays in a small SMT package to use.

    Yeah, me too. I build a lot of VCO circuits for synths with 2n3904 matched pairs for oscillators. I used to use SSM2210's, but you can't find those anymore either. Options are really limited for transistor arrays.

    #12 7 years ago

    Doing the UDN7180A would be a bit more complex. Here is what each circuit looks like inside the UDN7180A

    Untitled_(resized).pngUntitled_(resized).png

    He is how WMS implemented discreet devices.

    Untitled_(resized).pngUntitled_(resized).png

    #13 7 years ago

    Pretty sure I have a sleeve of CA3081s in my parts box if someone needs them for a repair. I will check tonight.

    #14 7 years ago

    Considering the Bally driver board is not that tight spaced and the board house was going to charge me the same price for both layouts. I went with the bigger one. Figure no need to try and bend and cram transistors on there if not needed. Went with through hole transistors for ease of assemble.

    Depending on what my time is worth to assemble them, they are cheaper than used pulls of CA3081.

    Takes about a month to get the PCBs from the board house.

    #15 7 years ago
    Quoted from barakandl:

    Considering the Bally driver board is not that tight spaced and the board house was going to charge me the same price for both layouts. I went with the bigger one. Figure no need to try and bend and cram transistors on there if not needed. Went with through hole transistors for ease of assemble.
    Depending on what my time is worth to assemble them, they are cheaper than used pulls of CA3081.
    Takes about a month to get the PCBs from the board house.

    @Andrew:

    What do you think of the arrangement in the following layout, should be smaller and pretty easy to solder for DIY

    CA3081_(resized).JPGCA3081_(resized).JPG

    #16 7 years ago
    Quoted from cody_chunn:

    This is what we're going to have to do for those Williams display chips...

    Quoted from barakandl:

    Doing the UDN7180A would be a bit more complex. Here is what each circuit looks like inside the UDN7180A

    He is how WMS implemented discreet devices.

    Indeed, the 7180-Adapter is much more complex and cannot be made as small as the IC itself

    UDN7180-Adapter_(resized).JPGUDN7180-Adapter_(resized).JPG

    #17 7 years ago
    Quoted from german-pinball:

    @Andrew:
    What do you think of the arrangement in the following layout, should be smaller and pretty easy to solder for DIY

    I think it is fantastic.

    I get a bit OCD about right angles of tracks and parts being placed all in the same direction. But for something like this, reduction of size is important so it fits on all pcbs.

    #18 7 years ago
    Quoted from barakandl:

    I think it is fantastic.
    I get a bit OCD about right angles of tracks and parts being placed all in the same direction. But for something like this, reduction of size is important so it fits on all pcbs.

    Me too, and having too many vias as well and jumpers. I'll re-design board layouts like 8 times to get it as tight as possible, even just for single boards for my own use. That comes naturally after building your first few crappy designs. Some of the earlier boards I etched myself when I was learning look pretty horrible, and most of those were mostly single sided too. At least most of them worked, but they're ugly.

    #19 7 years ago
    Quoted from thedefog:

    Me too, and having too many vias as well and jumpers. I'll re-design board layouts like 8 times to get it as tight as possible, even just for single boards for my own use. That comes naturally after building your first few crappy designs. Some of the earlier boards I etched myself when I was learning look pretty horrible, and most of those were mostly single sided too. At least most of them worked, but they're ugly.

    yep. my first few nvram pcbs. while 100% functional, i look at them now and go, oh geeze. like anything, you get better with practice. im still pretty fresh at it.

    #20 7 years ago
    Quoted from barakandl:

    I think it is fantastic.
    I get a bit OCD about right angles of tracks and parts being placed all in the same direction. But for something like this, reduction of size is important so it fits on all pcbs.

    @Andrew: Some more inspiration

    CA3081-Adapter_(resized).JPGCA3081-Adapter_(resized).JPG

    #21 7 years ago
    Quoted from barakandl:

    yep. my first few nvram pcbs. while 100% functional, i look at them now and go, oh geeze. like anything, you get better with practice. im still pretty fresh at it.

    PCB layout is something you have to always be like 12 steps ahead on, and no way to know how to do that until you've made a bunch of them. My cousin does multi-layer boards. I have no clue how he does it. There is all kinds of weird shit you have to do with heat venting vias and grounding and whatnot.

    #22 7 years ago
    Quoted from german-pinball:

    @Andrew: Some more inspiration

    Looks cool! Check the common emitter trace on your compact layout. The common buss isn't tied to the external pin. Also, by moving a coupe traces, you could easily make it single sided!

    #23 7 years ago
    Quoted from Schwaggs:

    Looks cool! Check the common emitter trace on your compact layout. The common buss isn't tied to the external pin. Also, by moving a coupe traces, you could easily make it single sided!

    Yeah, i think you have Pin 4 and 5 mixed up. P 5 is marked "substrate" on the ca3081 data sheet and grounded on the bally board (which i did on mine 5-15 together), but the idea is good. I like that layout with them all in a row.

    #24 7 years ago

    I didn't know there were this many pinsiders that did PCB layouts. Pretty cool.

    3 weeks later
    #25 7 years ago

    It works. Considering selling these as a kit. You would get a sheet of blank PCBs, headers, and 2n4401 transistors. Assembling them yourself, they would be cheaper than buying CA3081.

    Let me know what you think.

    20160822_122820 (resized).jpg20160822_122820 (resized).jpg
    20160822_123328 (resized).jpg20160822_123328 (resized).jpg

    #26 7 years ago

    I was going to try and do this in a IC socket, but this is way much better!!!

    #27 7 years ago

    I lIke it!

    #28 7 years ago

    Love it. Will certainly order some.

    #29 7 years ago

    This is beauty Andrew and Co. I love this kind of old school electronics.
    Maybe you could breadboard up the next hack on something like this:
    https://pinside.com/pinball/forum/topic/for-you-breadboarding-buffs-out-there

    #30 7 years ago

    I would be down for a couple. I need to order some more of your other chips anyway.

    #31 7 years ago

    I have them on my website now. Made a marketplace listing too.

    $2 each in a 10 pack.. wowowowow =D

    https://pinside.com/pinball/market/classifieds/ad/38403

    #32 7 years ago

    Are the CA3081's listed on eBay from China not working substitutes? Just curious.

    #33 7 years ago
    Quoted from acebathound:

    Are the CA3081's listed on eBay from China not working substitutes? Just curious.

    I was using CA3081 from China. They usually worked, but i had a few issues from a single bad transistor to completely dead. CA3081 was discontinued a while ago. Assume all of them from China are a used pull which is probably not tested.

    #34 7 years ago

    Hi
    Normally its only one transistor that's defective in the pack. I normally cut the corresponding chip legs for the base & collector flush to the chip body. Remove the legs and clear the pcb holes then just straddle and solder a BC548 across the chip body. Here's a Flash Gordon that i did recently. Thinking about it you could do this on the underside of the board hide the re-work.
    Cheers Bob

    ca3081 (resized).jpgca3081 (resized).jpg

    #35 7 years ago
    Quoted from pinballtoys:

    Hi
    Normally its only one transistor that's defective in the pack. I normally cut the corresponding chip legs for the base & collector flush to the chip body. Remove the legs and clear the pcb holes then just straddle and solder a BC548 across the chip body. Here's a Flash Gordon that i did recently. Thinking about it you could do this on the underside of the board hide the re-work.
    Cheers Bob

    Hi Bob,

    This kind of fix is what inspired me to make the adapters. Usually it is is one transistor going out, but sometimes the common leg has a problem which makes all 7 transistors not work

    2 years later
    #36 5 years ago

    My Strikes & Spares had a locked left pop bumper. I diagnosed it to the U3 on the solenoid driver. Luckily, I found this thread, and I purchased the replacements from Pinball Electronics last week. The part was built and installed within an hour today. The machine is back up and running. Thank you!!!

    3 years later
    #37 2 years ago
    Quoted from barakandl:

    I pulled off a hack today. Dead transistor inside of the CA3081. I opened my part drawer and found I was out of the CA3081. To get the board going i decided to swap in a single 2n4401 transistor.
    All I did was snip off the bad associated CA3081 legs. Desolder the pads clean. Stuff collector and base into the appropriate pins of the CA3081. Emitter is all common together inside the CA3081 and attached to ground. Pin 5 and 15 of the CA3081 are grounded so you can use those, or like i did, just find a nearby ground pad that was most convenient.

    It is so handy having this forum. I bought a machine with a melted coil sleeve for the drop target reset coil, a vaporised trace on the SDB, a shorted Q11.
    So I got on to putting correct fuses into the machine, checking all voltages on the rectifier board and SDB and then replacing the melted coil, fixing the trace on the board, replacing the Q11.

    Unfortunately the coil locked on when the machine powered up. Working back through the schematics I switched the TIP 102 at Q11 just in case it was dodgy, tested it's associated diode and resistor - all seemed OK. Board back in - power on - locked on coil again.

    Back to the schematics and worked my way back to pin 4 and 6 on the U3 - found the problem. So needed a CA3081 to fix the problem - can't find one, none in the local stores, can't wait a week for one in the post. Then I found this post.

    I had a 2N3904 in my MPU corrosion repair kit - so I checked out it's datasheet, looks like it will do the job. The PCB layouts really helped me understand the IC and I just clipped the legs 4 and 6 and did as barakandl did in the picture above.

    Back in the machine, power on, working beautifully.

    I don't know what we would do without you guys, who share your knowledge on this forum.

    Photo of my go at the “hack” below.
    1DDBF49B-9379-40AD-9514-1D33AE85EBE0 (resized).jpeg1DDBF49B-9379-40AD-9514-1D33AE85EBE0 (resized).jpeg

    #38 2 years ago
    Quoted from Grefla:

    Back in the machine, power on, working beautifully.

    In your case you could have swapped U3 with U4 because pins 4 and 6 of U4 aren't used.

    #39 2 years ago
    Quoted from Quench:

    In your case you could have swapped U3 with U4 because pins 4 and 6 of U4 aren't used.

    Oh. That is worth knowing. Thanks Quench

    8 months later
    #40 1 year ago
    Quoted from german-pinball:

    @Andrew: Some more inspiration
    [quoted image]

    Hi

    I'm trying to solve an issue with my CA3081 and am using this diagram as a guide. I'm just wondering - are pin 4 and 5 correct?

    pasted_image (resized).pngpasted_image (resized).png
    #41 1 year ago

    Looks like you are correct - 4 & 5 should be swapped. Pin 5 is not needed as an external connection.

    The fourth transistor down (on that PCB layout you posted) should have its collector to P4 and base is P6.

    pasted_image (resized).pngpasted_image (resized).png

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