TheHighNibble
S132 not working #96
Replies: 5 comments 10 replies
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well, to start, you do not need an oscilloscope but you do need a voltmeter because you apparently have a power problem. To start with, unplug the S132 from the Imsai and then power it alone with the 7.5v power source. You did not specify but I assume you are using a 7.5v DC power source and that the polarity at the barrel plug is correct for the S132? |
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Thank you for responding. I did try figuring out the issue after putting the S132 together with a multimeter, but we weren't getting anywhere. Anyhow, that's an interesting question about whether the polarity is correct. Just checked - the inside is positive according to both the multimeter and the adapter's indication. BTW, it's 1 amp output. |
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Now, if I place neg on the nut that holds in the regulator and touch the positive to the inside leg of the regulator, I get under 5V. I tried testing some other points on the board to see if I was getting 5V anywhere, but the thing that because the regulator gets so hot so quickly, I could already smell the heat and unplugged it. |
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Curtis, first of all, I do not have one of these devices and therefore have not built one either. so I am kind of flying blind trying to assist you. I see that there are no real assembly instructions so it is not up to the level that assembling the Imsai Replica was. My first thought is that you have one or more of the ics installed backwards. I would pay particular attention to the ones that are soldered in as the bill-of-materials indicate that they are very difficult to determine where pin 1 is. After that I notice that there could be several daughter boards that plug in to the main board. Unplug them all and try applying power again to see if one of them is the cause of the power overload.
From: Curtis
Sent: Monday, September 11, 2023 7:59 PM
To: thehighnibble/thehighnibble.github.io
Cc: pfcushing ; Comment
Subject: Re: [thehighnibble/thehighnibble.github.io] S132 not working (Discussion #96)
Now, if I place neg on the nut that holds in the regulator and touch the positive to the inside leg of the regulator, I get under 5V. I tried testing some other points on the board to see if I was getting 5V anywhere, but the thing that because the regulator gets so hot so quickly, I could already smell the heat and unplugged it.
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Everything's oriented correctly. As for unsoldering what I guess you mean by all the little boards that are a pain in the $*%# to solder, I'm afraid that's not really an option as they were so difficult to get soldered in without any shorts (and I'm not 100% sure that there still aren't any. I checked though across all of the neighboring connections to see if there was no resistance, which would be a clue as to possible shorting.) But also, some are so tightly packed in that I don't think I could possibly get them out anyhow (unless I were to remove other components). This is why I was hoping someone could suggest a way of working across the board with a multimeter or oscilloscope to figure out where the problem might be. |
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I just realized one of my push buttons is not aligned the same as in the author's pic. Just wrote about that in a separate (new) post. |
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Sorry, I didn't know the option boards were soldered to the main board. I thought they all plugged-in on header pins. Guess I can't help you.
From: Curtis
Sent: Tuesday, September 12, 2023 7:28 PM
To: thehighnibble/thehighnibble.github.io
Cc: pfcushing ; Comment
Subject: Re: [thehighnibble/thehighnibble.github.io] S132 not working (Discussion #96)
Everything's oriented correctly. As for unsoldering what I guess you mean by all the little boards that are a pain in the $*%# to solder, I'm afraid that's not really an option as they were so difficult to get soldered in without any shorts (and I'm not 100% sure that there still aren't any. I checked though across all of the neighboring connections to see if there was no resistance, which would be a clue as to possible shorting.) But also, some are so tightly packed in that I don't think I could possibly get them out anyhow (unless I were to remove other components). This is why I was hoping someone could suggest a way of working across the board with a multimeter or oscilloscope to figure out where the problem might be.
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Does the system work when you use the USB lead, and thus bypass the power regulator? I have the S132, and I just continue to use USB power. |
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You must be talking about USB power through the IMSAI and not through the USB on the S132 itself, since that is just for the keyboard. Or is there some other "lead" that I'm not aware of. |
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When you power the IMSAI over USB, the USB lead is connected directly to the microcontroller. |
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Let's take a step back. |
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It's possible you have a weedy USB power supply, so check that first. And don't forget the jumper to pick between USB and external power. First thing I would do is check the board to make sure all components are in the correct place, and correct orientation. Then the hard work: looking for shorts, especially around the SMD soldering. After a visual inspection, break out the multimeter and check all the pins on the SMD devices for shorts. The regulator will get hot, that's what they do. I don't think that's necessarily a red flag, although if it's crazy super duper hot that implies it has broken and I would replace it. But if the jumper is set for USB power and the S132 still doesn't work, that probably means it's not the regulator, so keep looking for shorts. |
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What is the function of the jumper next to the barrel power connector? It is not clearly documented anywhere in the documentation. I believe it may bypass the 7805 regulator and feed whatever voltage is supplied on the barrel connector directly to the S132 and IMSAI. That would be used to supply a regulated +5 volts to the system. If this is the case and you installed the jumper while applying anything over 5 volts to the barrel connector, you may have damaged some of the components in the system. If the jumper is used to select external unregulated power to the 7805 through the barrel connector, you should be safe. Lack of documentation in this case could be dangerous! EDIT: Dave confirmed that installing the jumper bypasses the 7805 regulator and is used if feeding regulated +5 to the board from an external source. If you installed the jumper and supplied > 5 volts regulated to the barrel connector, damage may have occurred to the components with a tight 5 volt supply voltage spec (The 74-series logic, for example). Don |
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I've been following this thread and I'm still confused. I guess I'm dense. Is the following correct: If the 5V Select jumper is installed then you need to power the S-132 from the IMSAI ESP32 USB port and should not use the barrel connector. If the 5V Select jumper is removed then you should use the barrel connector to supply power to both the S-132 and the IMSAI and the USB cable should be removed from the IMSAI ESP32 USB socket. Also what voltage range is acceptable on the barrel connector. It looks like it could be 5V to 12V. Center pin is always positive. Randy |
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Jumper installed: Power from ESP32 USB OR from the barrel jack with REGULATEDv+5 ONLY. Jumper not installed: Power from ESP32 OR from the barrel jack with unregulated voltage > 6 volts, using the on-board regulator. |
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So I finally got a handheld oscilloscope with the hope that it might help resolve why my S132 isn't working.
To recap. If I plug into the IMSAI directly with the S132 attached, a light on the PICO very briefly flickers. If I plug in a 7.5 V barrel socket into the S132, the IMSAI doesn't work, but worse the linear regulator next to the plug gets extremely hot. I don't have a 5V power supply with a barrel socket to try in the S132, but I do have a 5.6V? Anyhow, it shouldn't matter as I'm sure there's probably some short on the S132? I've looked over everything with a magnifying glass and an electronic microscope and don't really see any shorts.
I'd really appreciate any ideas about how to go about figuring out where I messed up. Note that I am not an electrician by any means, so please if you willing to provide any help be very specific and basic about what I need to test.
Thanks for any input!!!!
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