EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: GelatinousSlime on January 10, 2017, 04:44:40 am

Title: Mastech MS8268 repair
Post by: GelatinousSlime on January 10, 2017, 04:44:40 am
I purchased a MS8266 2 years ago and most of that time it has been sitting in a drawer unused. I've only ever used the basic functions like DC volts <=12v and ohm measurements, and continuity. So very light weight use and no chance of doing anything stupid and blowing it up. A few days ago I was measuring some 3.3v dc stuff on a breadboarded prototype project and noticed the display flickering and very slow autoranging, almost like each flicker was a reset and it had to start over. Eventually it stopped working altogether, I get no display at all and no sound (ex put it in continuity mode and touched the leads together with no tone output), no warning lights on the inputs if plugged into the wrong place, etc. From what I can tell it is 100% dead (almost like no batteries are even installed) EXCEPT for the back-light which still works exactly as before if I press the back light button. The back-light is the only sign of life I've gotten from the meter. I've opened it up, replaced batteries and checked the fuse, etc. I'm for sure a newbie so I was mostly looking for obvious signs like loose components. I haven't looked in detail at all the SMD components to see if any of those are loose but I'll probably do that next. Are there any general pointers to help me troubleshoot this meter or should I just give up because it's not worth it for a cheap meter like this?  I do plan to buy a nicer meter soon because I've really started to take renewed interest in tinkering with electronics projects (haven't done much of anything in 10 years now). I almost pulled the trigger earlier today on the EEVblog BM235 on Amazon, but decided not to be impulsive and research first. Once I decided to buy it and went back a few hours later its now saying unavailable :( I've only been watching EEVblog for a few weeks now and hadn't ventured back to many previous episodes yet to know much about the meter or that it was a fairly hot commodity until it was too late... oh well. Regardless of when I do I get a nicer meter, I'd still like to fix this one if reasonably possible to have as a backup and to use in the garage, etc.

Thanks
Title: Re: Mastech MS8268 repair
Post by: GelatinousSlime on January 10, 2017, 04:49:56 pm
I took one more look around the board and it all looks neat and clean. No components show any sign of damage. I cleaned the contacts for the range switch even though they looked fine to me. Put it all back together and still nothing but the backlight.  So for now I think I'll just give up and throw it back into a drawer to take another stab at repair later just for fun after I know a bit more about what I'm doing.

I checked Amazon again this morning and it was back to showing the EEVblog BM235 meter back in stock so I grabbed it quick as I could. It was listed as Prime eligible but is reporting a delivery estimate a week out rather than two days. It also switched right back to unavailable right after I completed my order, so I hope I actually get it! Since it has a delay and I'm a little worried it might have actually been an error and could get canceled, as well as me kinda needing a meter asap so I can continue on my little project I decided to also pick up a Uni-T UT61E as a cheaper second meter but still being a good step up from the crappy Mastech that died after extremely light low voltage use...
Title: Re: Mastech MS8268 repair
Post by: fable on January 10, 2017, 05:22:31 pm
Hi. Did you tried replacing the battery? I have the same dmm and when battery is low or it's cold in my workshop I must turn it on and off multiple times before it shows something on display.
Sorry for my bad English
Title: Re: Mastech MS8268 repair
Post by: GelatinousSlime on January 10, 2017, 08:15:45 pm
Yep, first thing I did :) It WAS cold in my make shift lab, but I also brought the meter upstairs into a warm room and left it there for a full 24 hours with no change. I've flipped the range switch around dozens of times at this point and never got anything out of it at all. I'm assuming the chipset is just dead and I'll never bring it back to life, but like I said I'll just shove it in a drawer for now and revisit it later when I have more experience to draw from.