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Thread: 4-slot keeps killing the battery

  1. #1
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    4-slot keeps killing the battery

    I have a 4-slot that (mostly) miraculously survived being underwater a couple days during a flood. I had to replace the backup ram to get it to boot and play again but it now does that quite nicely.

    Unfortunately, it now kills the battery within a day or so of powering off the cabinet. When I turn it back on, all the soft dips are lost and when I go to reset them and the calendar, I find that the calendar is counting up the time at an incredibly fast rate. Once I reset the calendar, it works correctly until the cabinet is powered off.

    This is new behavior. Before the flood damage, it could go weeks or even months on a single CR2032 and not lose anything.

    So I have a couple of questions:

    1. Is there anyone in the US that does repairs? I know of a few that used to but it seems everyone has retired.
    2. If not, where is the best place to start troubleshooting this? What tools should I have? Right now I have a decent soldering iron and basic hot air station, an Xprotolab Plain scope of questionable utility (3.3v inputs on the logic analyzer but I could probably add level shifters), and a DSO138 scope (very questionable utility).

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    Check the diodes in the charging circuit. I had one that was shorted and it was effectively making the battery power the entire board when the machine was off.

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    Quote Originally Posted by shadowkn55 View Post
    Check the diodes in the charging circuit. I had one that was shorted and it was effectively making the battery power the entire board when the machine was off.
    Ooo, nice! I'll definitely check on that.

  4. #4
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    It took longer than I expected to get back to this but the whole plague lockdown situation finally got me some spare time. I took some readings around the battery (brand new battery installed and this is what I found. These were measured with the positive probe on the positive battery terminal and negative probe at the labeled points.

    mvs voltage.jpg

    An interesting thing to note is that this is draining the battery so fast that even though the new battery measured ~3.33V before I put it in, it was down to ~3.29 after being in the board about 10 minutes.

    This second pic shows voltages measured with the negative probe at ground and positive probe at the labeled points:

    mvs voltage2.jpg

    Do these readings look right? If so, what are some other places I can check?
    Last edited by Murray; 04-04-2020 at 07:43 PM.

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    It seems correct. Is the backup ram still using original parts?

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    No. Those were replaced by parts I bought from arcadecomponents.com (Channelmaniac's store) back in 2018 (the system wouldn't boot at all before I did that).

    mvs backup ram.jpg

    The pic is a little blurry and there's some glare coming from a window but I assure you none of those pins are bridged. Also: "no-clean" solder paste, my ass.

    Edit: So I dug up datasheets for the original Toshiba chips and the new MOSEL chips. It looks like I was so concerned with getting chips that worked at all that I never considered power consumption. The datasheets don't have 1:1 comparisons in them (the Toshibas list "typical" mW/MHz where the MOSELs list "max" operating currents) but the Toshiba's "standby" spec and the MOSEL's "power down" spec paint a pretty clear picture.

    The Toshiba's standby current draw is 2A @ 5V where the MOSEL's "power down" is 550W. If my unit conversions are right (college was a long time ago), that puts just the standby power usage on the MOSELs at 8A greater than Toshibas.

    That absolutely could explain the rapid power drain, if that's the case.
    Last edited by Murray; 04-05-2020 at 12:34 PM.

  7. #7
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    Those should be low power variants. "No clean" doesn't mean it won't leave a mess. It means you don't have to clean it up after you're done.

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    I dug up a datasheet for the Mosel part and it two standby modes. 3mA for a "system on" but with /CE high and 100uA for the battery mode. Still magnitudes higher than 2uA from the Toshiba part. Try this any of these if you feel like replacing them again. They have significantly lower standby current consumption.

    https://www.digikey.com/product-deta...0-1-ND/4733140 (20uA)

    https://www.digikey.com/product-deta...4-5-ND/4498978 (5uA)

  9. #9
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    Quote Originally Posted by shadowkn55 View Post
    "No clean" doesn't mean it won't leave a mess. It means you don't have to clean it up after you're done.
    I know. Was just making a joke about my sloppy repair work.

    Quote Originally Posted by shadowkn55 View Post
    I dug up a datasheet for the Mosel part and it two standby modes. 3mA for a "system on" but with /CE high and 100uA for the battery mode. Still magnitudes higher than 2uA from the Toshiba part. Try this any of these if you feel like replacing them again. They have significantly lower standby current consumption.

    https://www.digikey.com/product-deta...0-1-ND/4733140 (20uA)

    https://www.digikey.com/product-deta...4-5-ND/4498978 (5uA)
    Nice! Especially the 5uA variant. I was able to find some NOS Toshiba chips on eBay but will probably order a few of the ones you linked just for grins. You never know when you're going to get something wonky from an eBay seller.

    I really appreciate your help with all this!

  10. #10
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    I'd say if you can still get the parts new from digikey or mouser, get it there. I'm gotten burned a few times trying to save a bucks buying parts off ebay. Wasn't worth the headache.

  11. #11
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    You could also just swap those Mosel chips with the Toshiba ones already on your board.

  12. #12
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    Quote Originally Posted by ack View Post
    You could also just swap those Mosel chips with the Toshiba ones already on your board.
    He could but that would be logical.

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    Quote Originally Posted by ack View Post
    You could also just swap those Mosel chips with the Toshiba ones already on your board.
    Quote Originally Posted by shadowkn55 View Post
    He could but that would be logical.
    No one really suggested that was an option. I already said my troubleshooting skills are weak for this kind of repair so I'm not sure what would indicate that I know those Toshibas don't also need to be low power. Wouldn't it be a reasonable assumption that if the Mosels were a problem in one place that they would be a problem in another as well? Also IMO there's far more risk to the board and components if I'm desoldering and moving around 4 chips than just the two problem ones. My SMT skills have improved a lot since I did the original swap but I'm definitely no expert.

    Anyway, the replacements came in and I installed them Thursday. So far so good. After several days, the battery has hardly discharged at all. One thing that was particularly interesting was that the when I booted it the first time, the calendar wasn't advancing ridiculously fast like it did after I had to replace a battery with the Mosels installed. Maybe those things were bum chips all along and it was a complete accident they were working as well as they were.

    So thank you again for all your help. It's really hard to express on a forum how good it feels to have something with such a huge amount of sentimental value finally brought back to working order after all these years.

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