BK Precision Dynascan Corporation 2806 Multimeter Repair.

I picked up this latest addition to my collection yesterday, a BK Precision Dynascan Corporation 2806 multimeter. It did not function. Neither the display nor the continuity beep. There is nothing about this particular model on the internet, I found one picture from Ebay and that was it.


The batteries were good (swapped them out anyway) and the fuse was good.


So I opened it up. At some point it had solvent of some sort spilled on it(?) or it was glued shut so prying took a bit of effort and was slightly destructive.


One side. Notice the input jacks are on their own PCB. Spoiler – you can see the problem in this picture, but it isn’t obvious.


The other side. The big input fuse was ok as well.


The switch solder points were corroded so I cleaned them up. I also doused the all the various switches contacts in contact cleaner.


Success? Sort of but no. It comes on but no matter what setting the large switch is set to, it only functions as a voltmeter. Hmmm…


I spied this little ding on the PCB. The trace is broken.



A quick and dirty repair (scrape the solder mask off and solder on a strand of copper wire)…


  
Each setting now works.

Stuff I Did And Am Doing, Places I Was.

I’m in the middle of a few projects right now, here are some interesting bits of things I’ve played with and stuff I’ve done in the past weeks. If I don’t post it now it’ll just sit and get all moldy.

   
Some rocks off of Yaquina Head.


My Cousin Jennifer and Cousin Saro visited from Boston.


Felice and Jennifer being all contemplative.


Yaquina Head lighthouse.


Max was lost in thought.


Sandstorm at Agate Beach.


I scored this Apple IIe computer at a yard sale for $5.00. This is bad as it’s the sort of thing I can get obsessed with. I have a reputation for hating Apple Products, but this retina display is awesome.


Well how the heck am I going to do that? Much learning ensued. I’ll have a separate post or two about it, but let me say that ADTPro is very cool.


This is the latest bit of research…


This was free at a yard sale. Felice said she doesn’t mind me opening the Philomath Vintage computer museum. It’s a word processor but I think it counts as a computer.


Ron wasn’t that bad looking. This was the only file on the floppy disk.


Oh…I discovered that the Internet Archive has a vast software archive. I always wanted to play Ogre on a computer running DOS. If you run it in Dosbox, use D-Fend. I have.


It’s there for the Apple IIe as well.


We missed the Steam-Up last year, but went this year. Gregg made us tee shirts from our logo (nonsequitur).


This is your hair on a giant squirrel cage fan.


Riding the rails.


Some really cool home made treadle woodworking tools.


And an antique one.


I told you I collect VOMs. Picked this up at the Steam-up swap meet for $1.00.


Ok, what is this thing? Found it at the OSU surplus sale. It’s a great argument starter, toss it into a room of engineers and they’ll rip each other apart.


A box for $3.00 at a yard sale.


More components…I’m getting lucky or nobody wants this stuff. The crimp pins are going to be handy and are surprisingly expensive.


Speaking of things I don’t know about, what are these?

Repairing And Understanding A Zalman Fanmate-2 Fan Speed Controller

UPDATE: I made an assumption...that was wrong. The regulator is a 7805, the resistor is a 710 ohm (708 ohms measured) and the potentiometer is 1K ohm. It turns out that reading resistor color bands is difficult without good lighting and measuring components in circuit can introduce errors. See here for an updated analysis. Although some of this post should be useful still.
    
I picked this up at a yard sale a year ago. A Zalman Fanmate-2 computer case fan speed controller. For some reason the 3 wire connector for the motherboard had been cut.

Not the most exciting thing to look at.

I pried the housing apart. Surprisingly it did not break.

A neat little layout. The heat sink covers up a resistor and what I presume is an LM317T variable voltage regulator (could be something else I suppose but it’s behaving like one). Read the datasheet!

You can see the three legs of the LM317. It’s bolted to the heatsink (which also means that its live with the output voltage).

Some LM317Ts from my parts drawer.

My general impression of the circuit which seems to follow the classic LM317 voltage regulator, without any capacitors. It was nearly impossible to take a picture of the resistor, but it has bands (red, none, black, black, red, purple) that indicate it’s a 200 Ohm, 2% resistor. The potentiometer has a variable resistance between 637 Ohms and 1721Ohms. Plugging those values into an LM317T calculator it shows a voltage 5.23V and 12.01V. Because there is a voltage drop from supply voltage on the regulator (that depends on mumble, mumble, mumble, more math than I want to do), the maximum voltage it can produce from 12V should be about  10V. In real life I get a voltage of between 5.13V and 10.5V with a fan hooked up. the power supply voltage, resistor, potentiometer, load from the fan and my consumer grade voltmeter all conspire to make this less than an exact science.

Oh yeah, I soldered on a connector.

Running it out of the case to measure temperature on the heatsink (90 deg. in a 78 deg. room)

Just running a fan at different speeds. Fun.