BK Precision 120p teardown - Page 1
Forum section: electronics / testgear

author: nullbert
author_rank: Newbie
timestamp: May 17, 2015, 06:11:48 pm
content: Just yesterday, I got an old BK Precision model 120p multimeter at a local thrift shop for $5. I think Dave's fascination of vintage/antique test equipment has gotten to me. The multimeter didn't include any test leads, so I haven't been able to see if it works yet, and even if it did come with leads, some (all but one really) of the battery connections are either corroded or disintegrated.The meter did come in what I assume is its original carry case and instruction manual. Both have seen much better days, as you will see.I'll state right now that I really don't know too much about electronics; I can use a multimeter correctly without overloading it, I can setup a scope without using the "auto" button, I can (and still am in the process of) make a stepper motor-driven tachometer with an arduino, but I don't know enough about anything else to make any kind of meaningful comments on the pictures I've taken, so I'll only comment of one or two of the pics.Many of the pictures are duplicates with and w/o flash so you can see different details in different pictures.I'll apologize in advance for the picture quality; I took these with a Canon 20D that has about the same image quality as a modern-day cell phone.Enough talk, let's get started!Yes, that is mold on the instruction manual. I'm quite sure this meter has sat in someones garage or basement for about 30 years. The pages inside are just as bad; I scanned the whole manual.There's the disintegrating 9V battery connector. And to think I, just a month ago, took apart an alarm clock and threw out the 9V battery connector it had. That'll teach me not to throw anything away.These were the batteries that were in the meter. About what you would expect with their age... The D cell measured 100mV, the 9V measured 10mV. The 9V battery was still connected to the meter when I opened the battery compartment. I tried my best to delicately remove it, but the negative wire from the connector broke off, the corresponding clip was stuck on the battery and had some disgusting resin-like substance on it.Last used around '83... I wasn't even born then.Four machine screws into threaded inserts with only one missing lock washer.Now for the close-ups!Now the scans of the instruction manualHere's a link to the photobucket album:http://s1276.photobucket.com/user/Glaveyy/library/bk%20multimeterWell, that's all folks, I hope you enjoyed yourselves.

author: commongrounder
author_rank: Frequent Contributor
timestamp: May 17, 2015, 07:09:39 pm
content: B&K's copy of the Simpson 260 multimeter. From the components inside, I'd guess made in Japan.

author: VintageNut
author_rank: Frequent Contributor
timestamp: May 17, 2015, 07:34:03 pm
content: I bet that it smells like a musty basement. Reminds me of a Heathkit O-3 oscilloscope I had years ago. It had the green film and smelled bad, but it worked.If you clean it up, install new battery clip and wires, it should work. The caps may be dried out/defective.Analog meters are good for some things that digital meters are not. Kind of a preference thing. The price was certainly right.

author: Vgkid
author_rank: Super Contributor
timestamp: May 17, 2015, 07:53:03 pm
content: Definetly get it working. It reminds me of a cross between the older and newer Simpson 260's.

author: nullbert
author_rank: Newbie
timestamp: May 17, 2015, 10:38:16 pm
content: Quote from: VintageNut on May 17, 2015, 07:34:03 pmIt certainly does have a... rich aroma about it. Once I make some suitable test leads and try my best to remove the corrosion, I'll see if it still works. Unfortunately, I don't have anyrealprecision voltage references to compare it to, just 2 cheap radio shack DMMs, one cheap-ish extech DMM, and a tektronix 2212 scope to compare readings with.

author: VintageNut
author_rank: Frequent Contributor
timestamp: May 26, 2015, 06:53:28 pm
content: My suggestion once you have it running is to measure a 1.5V DC battery and a 9V battery. That is plenty good enough for an analog meter to know if it is working.