History of Tachikawa (TMK)

[fanOfeeDIY]

Thank you for taking the time to check.  I would have bet on it protecting the current input.  It's strange how they would change how it was wired but maintain the same functionality.   I wonder if this change was a labor savings. 

Was or is your meter behaving differently when it does not have the fuse?

I am not completely understanding how the rotary switch work on the schematic (model AMK-200, you have posted on this thread), however the fuse seems to work for voltage and current but not for resistance.
https://www.eevblog.com/forum/testgear/history-of-tachikawa-(tmk)/msg1318383/#msg1318383

I just would like to know about this meter and your knowledge of surge protection knowledge on your youtube videos.

[mzacharias]

I constantly peruse eBay for mutimeters. I have seen many variations on the theme of this IBM model. Lafayette had quite a few, Radio Shack even had one or two, maybe even Eico / TruVom (spelling?) I believe the OEM companies like TMK and Kamoden had agreements with Lafayette, Radio Shack, et al prohibiting them from directly competing in the U.S. market. This I believe is why you rarely see Kamoden or TMK branded VOM's in the U.S. but see many of their products from Radio Shack, Mura, and others.

[coppice]

I constantly peruse eBay for mutimeters. I have seen many variations on the theme of this IBM model. Lafayette had quite a few, Radio Shack even had one or two, maybe even Eico / TruVom (spelling?) I believe the OEM companies like TMK and Kamoden had agreements with Lafayette, Radio Shack, et al prohibiting them from directly competing in the U.S. market. This I believe is why you rarely see Kamoden or TMK branded VOM's in the U.S. but see many of their products from Radio Shack, Mura, and others.

Was Lafayette a brand name of Radio Shack/Tandy? I remember seeing some TMK meters in the UK branded as Lafayette after Tandy starting opening shops there.

[joeqsmith]

Was or is your meter behaving differently when it does not have the fuse?

Mine originally worked like your dad's.   The fuse only protected the resistance measurement.  I changed the design to protect both the resistance and current measurements.   The voltage still works without the fuse.  The only reason I made this change was if I decide to use the meter in some future video for current, I wanted the added protection. 

I am not completely understanding how the rotary switch work on the schematic (model AMK-200, you have posted on this thread), however the fuse seems to work for voltage and current but not for resistance.

In that schematic, the fuse is in-line with everything.   I am not sure how much protection it would really provide (for the meter) but it's better than nothing.   I don't like meters that will not display the voltage with a blown fuse.   

In the attached, I have marked the path for the 250mA setting.

I just would like to know about this meter and your knowledge of surge protection knowledge on your youtube videos.

Those few videos where I modified the Kasuntest ZT102 and the UNI-T UT61E were my attempts at explaining it.  From what I have seen most of the meters, well the ones that actually survive to some decent levels anyway, basically take the same approach to hardening the front end.     

[fanOfeeDIY]

Was or is your meter behaving differently when it does not have the fuse?

Mine originally worked like your dad's.   The fuse only protected the resistance measurement.  I changed the design to protect both the resistance and current measurements.   The voltage still works without the fuse.  The only reason I made this change was if I decide to use the meter in some future video for current, I wanted the added protection. 

I see, even I did not change the internal wiring, and it was different from yours, the fuse on my meter (or dad's ) was only for resistant and the fuse was not protecting the voltage and current.

I have an other analog meter made by Sanwa, and when I removed the fuse, all voltage, current and resistance stopped working.
Different analog meters seem to have different approach.

Looking forward for your future video.

[fanOfeeDIY]

I am not completely understanding how the rotary switch work on the schematic (model AMK-200, you have posted on this thread), however the fuse seems to work for voltage and current but not for resistance.

In that schematic, the fuse is in-line with everything.   I am not sure how much protection it would really provide (for the meter) but it's better than nothing.   I don't like meters that will not display the voltage with a blown fuse.   

In the attached, I have marked the path for the 250mA setting.

Thank you for detail diagram with marking. I completely understand how the rotary switch would be written in the schematics now.

I was playing with this meter and I realized that it is nice to be able to use the own meter for battery checking and the fuse, and this analog tester is able to do it.

[Tepe]

The insides of my TMK model 200:


The outside and original box:


(Edited to add picture of the outside of the meter)

[joeqsmith]

The closest schematic I found to my 200C was for the TP-5SN.  I used it as a starting point.  Keep in mind, there may be mistakes.   

The insides of my TMK model 200:
..
The outside and original box:

Very nice.  I had wondered if these had a fuse in them or not. 

[Tepe]

Very nice.  I had wondered if these had a fuse in them or not.

Here's a photo of the schematics part of the model 200 instructions.
As it says, it came with a spare fuse. The tape residue seen in the picture of the insides, is where the spare was placed

[joeqsmith]

Thanks for taking the time to provide that picture.  There is very little written information I can find on the net about these meters and every little bit helps.   

It's interesting that your meter has the fuse in series with the common to provide some protecting in every function.  It must have been around the time that they started thinking that they may not want disable the voltage measurements.   Then again, I have seen a few modern meters that do this same thing. 

[Tepe]

Thanks for taking the time to provide that picture.  There is very little written information I can find on the net about these meters and every little bit helps.   

It's interesting that your meter has the fuse in series with the common to provide some protecting in every function.  It must have been around the time that they started thinking that they may not want disable the voltage measurements.   Then again, I have seen a few modern meters that do this same thing.

My warranty card states that the importer tested the instrument November 12, 1979. I guess it is reasonable to assume that it isn't a lot older than that.

[timb]

I'm sure you could make up all sorts of stories. I doubt an IBM service person would make a house call to repair a personal typewriter.  It would make more sense they would send the typewrite to a repair shop. 

Actually, individuals could get a service contracts through IBM. If your Selectric broke, a repair tech would come out and fix it. They were very complex machines, mechanically and required specialized adjustments if certain parts were replaced.

IBM already had a nationwide network of repair techs in place, after all, what company wants to send each typewriter to a repair shop. So it makes sense they’d offer the contract to individuals and small businesses as well. A service contract was about $100, which wasn’t bad considering a Selectric could cost over $1000!

[coppice]

IBM already had a nationwide network of repair techs in place, after all, what company wants to send each typewriter to a repair shop. So it makes sense they’d offer the contract to individuals and small businesses as well. A service contract was about $100, which wasn’t bad considering a Selectric could cost over $1000!

The service contract for most IBM equipment worked out remarkably close to 10% of the purchase price in those days.

[fanOfeeDIY]

The outside and original box:

Just nice! With original box.

[DF1DA]

Hello Tepe,
thanks for the pictures. The photo of the instruction leaflet with schematics are very helpful. Reason:
It happened to me to find such an instrument at a second hand store during holiday in Denmark for just 20DKR. Comparing it with yours it might be an early version w/o the fuse on the common input, without protection diodes across the meter and with different labels on the inputs. Luckily the AA cells did not (yet) leak, of course now replaced by new ones.
Gerhard

[langlv]

Hello joeqsmith,
I got a TMK 100K, with design very similar to Simpson 269. I found a schematic on another forum, but in my VOM there is an additional relay (for overload protection?).
Hope you have some info abit it.
Best, and Happy New Lunar Year

Lang

[joeqsmith]

I don't see a relay in the schematic you linked.  Maybe you could trace that section out and post it.  We may be able to sort out its purpose from that.   I found a link showing a few pictures of the meter and talking about the 269. 

https://www.vintage-radio.net/forum/showthread.php?p=746757

[langlv]

Finally, it's not an overload protection, but a buzzer for continuity test.
The buzzer is not in part list, and is drawn as very discret circle in the schematic.
To achieve 10uA FS, the coil is quite large, almost 1 inch. I guess they did not make enough strong magnet. It's incredible that Triplett managed to build a 1uA FS with a smaller coil. 

[joeqsmith]

Funny to see the chain drive.  Looks like a gear split.  I wonder if you could have a set made from brass. 

[coppice]

I used to own a TMK 100k. I don't know where it went. It was an excellent instrument. The only weakness was the handle mounting. The bolts holding it could work undone, until you applied something to stop them. That chain drive approach allowed for a really nice layout inside, although like most multimeters of the time it must have taken someone quite a while to build it. I liked the way they tuned the 10A shunt.

It does have a buzzer for continuity, and it does not have overload protection. It has a nice wide resistance measurement range, but this requires a 15V battery which is probably hard to find these days. The use of a large 1.5V D cell for the lower resistance ranges kept the battery life high when using that buzzer a lot.

Being so sensitive, but with a really long pointer, you really need to use the meter damping "off" position when moving the meter, or it might prove a bit fragile.