Did I destroy my chip? - Page 1
Forum section: electronics / beginners

author: robotic
author_rank: Contributor
timestamp: July 10, 2017, 04:44:31 pm
content: So let's start off by saying that I am a beginner and have basic knowledge of circuits.So I was trying to 'fix' my thermal printer and now the stepper doesn't move.I thought it might be a power issue and added a 16v 1000uf cap... to the 'input power'. the input power was 7v.So I'm pretty sure I destroyed something, as I also inversed the cap... as nothing seemed to be happening (which was very dumb).So I have 2 thermal printers and they seem to use the same chips and design and compared them.The driver motor chip is 'A3906' Allegero (datasheet)The working one vs the not working one.The 2 CP (charge pump) caps on the working one show 7v when clicking feed. The broken one does not. (0v)The input signals voltage goes up on both when clicking 'feed'. and the broken one does print, except I have to pull the paper manually (as the servo doesn't do it).I did remove the servo and test it independently and it works.So my two thoughts are that either the capacitors are dead (which i kind of doubt) or the chip is dead.Is this correct? Also is there an alternative to this chip?Or I'll try to order it from aliexpress and perhaps painstakingly remove it and put a new one on. Also any tips for removing it as it has a soldered on pad (pad is a little dot on the back). I'm thinking of getting a hot air station, as I don't think it will work with a soldering iron.

author: metrologist
author_rank: Super Contributor
timestamp: July 10, 2017, 05:11:40 pm
content: connected to the power supply to the chip? I think polarized caps short when reverse biased, so maybe you burned out the 7V supply? Trace it back to its source...

author: robotic
author_rank: Contributor
timestamp: July 10, 2017, 06:42:16 pm
content: the input on the chip is still 7V. I tried to do some micro-soldering and kind of failed (probably salvageable, but I give up). So nevermind. I think i could have bypassed the chip and used another h bridge chip to drive it. I used a logic analyzer and saw that steps the chip was making and may have probably worked. Everything is too tiny and I've wasted enough time on it and could easily buy another for $20 (which technically my time is worth more then). Spend more then 10hr probably diagnosing it.Learned nothing really, except don't use capacitors to just 'test' if you don't know what your doing lol.

author: bson
author_rank: Unknown
timestamp: July 10, 2017, 09:18:04 pm
content: If you inserted a charged 1mF cap backwards... It's probably toast.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 11, 2017, 09:40:52 am
content: Quote from: robotic on July 10, 2017, 06:42:16 pmThat could have been a plan.Quote from: robotic on July 10, 2017, 06:42:16 pmModern things are very small. Magnification is a must. Things get much easier under a stereo widefield microscope or a magnifier of some kind.Quote from: robotic on July 10, 2017, 06:42:16 pmThat's 10hrs entertainment

author: Codebird
author_rank: Regular Contributor
timestamp: July 11, 2017, 10:23:16 am
content: Look on the upside: Broken down old printers are easily turned into stepper motors for future projects.

author: robotic
author_rank: Contributor
timestamp: July 11, 2017, 09:35:22 pm
content: Quote from: Codebird on July 11, 2017, 10:23:16 amit's one of those mini thermal printers, so not too much use. however I could use the whole device to just 'feed' paper.