Micro-Kim not quite there yet... 1uF capacitor polarity?

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Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby blatboy » Mar Thu 01, 2012 10:48 pm

I had a wonderful time putting together my Micro-Kim but sadly I can't seem to get it to work. It's the same symptom that many others have had. The power LED's on, but no one is at home. (The segments don't light up when reset is pressed)

This was my first "serious" PCB project, though I've had some experience with beginner "learn to solder" projects and I've built a lot of audio cables for my studio. So, I'm sure my job on the Micro-Kim wasn't stellar. I did double check my work and it seems while the job isn't beautiful, everything seems to check out. I've also brought it to someone who works in electronics and he thought it looked ok.

In my research and troubleshooting, it seems I had a printout of rev 1 of the manual, and I'm curious if perhaps I put my 1uF capacitor in backwards. Since I've already installed it, I can't tell how long the leads were. There is a "35+" on one side of the capacitor. Is that "+" is referring to the lead it is closest to? If so, that would make me think the "+" should also be closer to the outside of the board, yes? If this is indeed the case, then mine is in backwards. However, before I remove it and turn it around I wanted to see if I'm reading this correctly.

I've had the power on for at most 20 minutes while testing, and nothing exploded, so that's why I'm unsure if I'm incorrect on this. (Tho perhaps I've been frying everything? oy.)

Furthermore, and this may or may not be related... I'm using a 5V 2A power supply. I measure 5V going into the 7805, but only 4V (or a little less than that) coming out of it. So, it seems my voltage may be running a little low too. Is this possibly because of the capacitor issue (my brain doesn't think so, but I'm pretty inexperienced) or do I need to get a power supply with a little more voltage?

Thanks so much! I'm really looking forward to having this work, and building more kits! I've found the build process to be relaxing and enjoyable. It's like knitting for nerds. Hellzyeah!
Last edited by blatboy on Mar Fri 02, 2012 3:21 pm, edited 1 time in total.
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Re: Micro-Kim not quite there yet... 1u capacitor polarity?

Postby vbriel » Mar Fri 02, 2012 12:51 am

Well, to start, yes the 1uF cap needs to have the + closer to the edge of the board. This happens, not that big of a deal, but you need to reverse that. Try and heat and pull one side at a time, be careful to not burn up the outter hole or you will loose voltage to the part of the board.

5V is not enough incoming voltage for the voltage regulator. You need at a bare minimum 6V but 7 is better. Not only that, the supply needs to be at least 700mA or it might not supply enough current. Those 7 segment displays burn juice.

The main thing holding your board down is the 5V incoming voltage. 4V going out to 5V chips isn't going to work.

Keep 2 things in mind so you don't get discouraged.

1. MOS chips like the 6502, 6532 and SRAM are very sensitive to static damage. It can happen just in shipping. I sent a tested working board out last month that got zapped in the mail.
2. I can look at and most likely get your board up and running for you. I have a supply of chips to test with and other tools that you might not have. Not to mention, I designed it, so I know how it works.

The Micro-KIM is a little different than some of my other kits because if one little thing goes wrong, the whole board doesn't work. So, a blank display is very common. Heck, I've even run across simple things, like no jumper on JP1 or the user not pressing RESET to get the board going. Most people don't realize these boards back then didn't have auto-reset circuits so they had to be manually RESET after you turned it on. Auto reset circuits were nice but cost more to impliment so they were left off on early designs. The apple 1 was the same way, as well as many other boards of this era.

Anyways, try and turn the cap around, get a different supply and see if you get anything out of it. If not, email me at vbriel@yahoo.com and I'm more than happy to look it over. Ask anybody who's sent their boards in, I get it fixed or I swap it out. Who else does that? Still, I prefer you get it up and running because it is just a great feeling when you troubleshoot your board and get it to run.

Vince
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Re: Micro-Kim not quite there yet... 1u capacitor polarity?

Postby blatboy » Mar Fri 02, 2012 2:14 pm

Thanks so much for the quick reply.

I'll have that capacitor do an about face. And I'll try another power supply. I probably have one... I know I have 9V ones coming outta my ears. Would that be too much?
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Re: Micro-Kim not quite there yet... 1u capacitor polarity?

Postby vbriel » Mar Fri 02, 2012 2:16 pm

For short period (10-20 minutes) no problem. For the long road, 7.5-8V is the way to go. Heck, for a minute test, 12V would work but sinking that much voltage would get hot quick.
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Re: Micro-Kim not quite there yet... 1u capacitor polarity?

Postby blatboy » Mar Fri 02, 2012 2:19 pm

Awesome. That means I can do more testing today or this weekend. I'm going through my bin of power supplies now just in case I have the perfect (or an adjustable) one.

Thanks so much!
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Re: Micro-Kim not quite there yet... 1u capacitor polarity?

Postby blatboy » Mar Fri 02, 2012 2:27 pm

Amazing. I found an adjustable 300mA one that I can set to 7.5V. I'll rock that one.

I'll get back to you after I work on it.

Thanks again!
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Re: Micro-Kim not quite there yet... 1u capacitor polarity?

Postby blatboy » Mar Fri 02, 2012 2:51 pm

ooooh. you said 700mA. I'll try it with a 9V too (for a short time) as you suggested. Sorry for my continual posts here.
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby vbriel » Mar Fri 02, 2012 4:25 pm

Keep it coming, it is reading material for a lot of people.
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby blatboy » Mar Sun 04, 2012 3:19 pm

I've considered sending this as a PM, due to my incredible embarrassment on this... but if the people want reading material, I suppose I'll oblige and take the hit to my ego.

I feel like I've been indoctrinated this Sunday afternoon.

I took out the 1uF capacitor, accidentally taking one of the leads out of the disc. I just sorta shoved it back in and reattached the capacitor in correctly in the board. I figured I would pick up a new part on some other day but still see if I could get it working today. This bit of impatience was just the first little transgression before the big one...

Then I took a look at one of the power supplies I brought. It was a Roland 9V 1000mA wall wart I had borrowed from an early 90's-era synth I had lying around. I plugged it in, and hit the power switch... I heard a loud pop and saw a flash and magic smoke coming from the upper left hand corner of the board. I immediately turned off the power and unplugged it.

Stupid me didn't look at the polarity of the wall wart. What is it with me and polarity?

So, how bad is it? Looking at it nothing looks fried. When I put the 5V in that I was using before, the power LED doesn't light up anymore. Is it just a case of replacing a couple parts or do I pontentially have a board of deep fried chips here? I'd love to see if I can still get this working if you think it's just a matter of doing some testing and replacing of some parts. However, I know you are busy, and I don't want to waste your time. If I now have a doorstop, I'm prepared to order another and try again. It was my own inexperience, impatience, and inattention to detail that got me here, after all.
Last edited by blatboy on Mar Sun 04, 2012 3:34 pm, edited 1 time in total.
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby vbriel » Mar Sun 04, 2012 3:32 pm

Don't worry, it can be fixed, email me @ vbriel@yahoo.com to work out shipping it to me. The reason is because there might be a burnt trace but most likely the 5V regulator is bad. I can desolder it and put a new one on. I can also fix that bad hole for the 1uF cap too.

On the Altair micro I put a 1amp diode on board to keep from doing damage on reverse polarity, but at a power expense. Also because the power travels to another board via a ribbon cable, I felt it was a must. The issue will make for a good documentation to show how to fix the board.

Vince
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby blatboy » Mar Sun 04, 2012 4:19 pm

I'm happy to help you with your documentation. Ha! This, of course, was my plan all along. I'm here to help. ;)

email sent. Thanks.
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby vbriel » Mar Sun 04, 2012 4:34 pm

smoke, smoke, smoke! The more we resolve and document here, the more people that run into issues will have a source to read from. Sometimes I get a little busy when I get close to a project release or I'm going to a venue, so the community here is important.

If it makes you feel better, I had a 5V power supply that I was using directly on a circuit and I let the power input can touch the bare power supply board and smoked the power supply. It welded the power plug can to the fuse holder! For 1/2 a second it looked like a welder, blue bright light and everything.
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby blatboy » Mar Mon 12, 2012 1:26 pm

Ok... an update.

After messages with vbriel (who's been an amazing help) I replaced the 5V regulator, and it seems that was the only damage I caused when the magic smoke escaped. I tested the unit w/a 12V 1000mA PS, and I was back where I was. The power LED would come on, but no one was home even after pressing RESET.

Today I was just about to ship it back to vbriel, and I thought I'd do one more quick looksee. Sure enough, I had done a crap job of putting in those chips. Two of them had bent pins. I corrected that, and voila! I have a working Micro-KIM.

I'm still going to replace the 1uF capacitor that I had damaged while trying to remove it. I don't want that coming apart at a bad moment.

I'm ordering a proper PS today. When that comes I'll be able to use the Micro-KIM more than a few minutes at a time. Then I'll know for sure how it's shaping up.

Thanks again Vince for all your help! I really appreciate it!

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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby rwiker » Mar Mon 12, 2012 3:11 pm

You probably don't want to use a 12V supply for extended periods of time... the 5V regulator may burn out if you're feeding it at a too high voltage.
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Re: Micro-Kim not quite there yet... 1uF capacitor polarity?

Postby blatboy » Mar Mon 12, 2012 4:23 pm

I'm only using the 12V for testing at very short periods. I'm about to order a 7.5V one...

thanks!
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