bench multimeter pushbutton switches

[redwire]

Got a Wavetek/Amprobe/Meterman BDM-40 bench DMM with a broken pushbutton switch.
Looks like the buttons got hit and one broke the end and the contacts popped out. Ouch.

Service manual gives Alps part numbers that I have no data for:
3202-3500960 SPUN50A802-GW 12P*3 ,IL 12P*1 ,PP 6P*1 PP
3202-3701080 SW PUSH SPUN70A802 12P*4 18P*2 IL 6P*1PP

Closest I can find is Alps SPUN194700 4PDT. But ALPS catalog has momentary and latching parts and instead these switches stay in until the next button is pressed (i.e. V, A, ohms select buttons).
There must be a lever running between the switches for the one-of feature.
It looks like switch bank is in a metal rail. I'm not sure how that rail works.

Anyone worked with these switches, know if this whole bank has to be pulled or how the lever works between switches. Would I order momentary or latching?

[stj]

Re: bench multimeter pushbutton switches

the switches fit into a metal chanel with a sliding bar that releses one switch as you press the next.

as for the actual switch, the only difference between latching and momentary is a metal "S" shape pin that you can remove that is in the latching ones.

so you can use either.

[eccerr0r]

Re: bench multimeter pushbutton switches

It looks like you have a Intersil 7135-based DMM there (4½ digit integrating). I wonder if anyone tried "overclocking" these ADCs?

Mine (B&K) is really slow... if I could get it 33% to 50% faster that'd be nice...

Probably not though. When I was trying to compare the 7106/7107 based DMMs versus my LD110/LD111 DMMs, the 7106 are pitiful...

[redwire]

Re: bench multimeter pushbutton switches

I had to pull the entire switch bank, then pry up the locking tabs to get that switch out. The cam lever is just in the way otherwise. Note it includes a tiny spring, the kind that shoot into outer space when you aren't looking

Looks like Alps SPUN pushbutton assemblies are factory-made by sliding in the switches and then crimping the tabs. I see only push in/push out (latching) switches have a pin on the top.
I'd order the new switch but but no momentary 4PDT in Alps catalog.
I'd have to get SPUN194700 and pull the latching pin I guess?

I got the DMM free, save it from the garbage, and I think better quality than the $25 banggood things.


Yes I'd like to overclock it, it does need turbo. I got a 100kHz clock (2 readings/sec; and rejects 50/60/400Hz). Max. is 120kHz (1979 datasheet typo still there: 1200 kHz max. lol).

"The maximum conversion rate ... is limited by the frequency response of the comparator. The comparator in this [ICL7135] circuit follows the integrator ramp with a 3μs delay, and at a clock frequency of 160kHz (6μs period) half of the first reference integrate clock period is lost in delay. This means that the meter reading will change from 0 to 1 with a 50μV input, 1 to 2 with a 150μV input, 2 to 3 with a 250μV input, etc. This transition at mid-point is considered desirable by most users; however, if the clock frequency is increased appreciably above 160kHz, the instrument will flash “1” on noise peaks even when the input is shorted."

Teledyne (Microchip) obsolete TC835 can go to 200kHz and is pin-compatible; integrator cap change too but more info on overclocking is there. I'll look into it because I like fast update rate too.

[eccerr0r]

Re: bench multimeter pushbutton switches

I think mine's also 100KHz or so, just eyeballing it (should be 2.5 readings/sec?) I have an LD110 DMM that's closer to 4 or 5 readings/sec...

Would be interesting. I'm thinking I could just bodge a resistor in parallel if it's an RC clock oscillator, though I haven't taken a good look at what's generating the clock in my meter.

The power consumption of my meter is already pretty terrible, so I guess I don't care too much. I wish it could run 200 hours off a PP3 but probably the decoder and other logic is precluding that... (though it is LCD it uses UM2's because it eats so much power...)

[redwire]

Re: bench multimeter pushbutton switches

I can't get the spring in.

Held it in tweezers and as I released the tweezers, it shot across the room Hours later I found it, using a magnet.

The spring goes between two switches and presses the lock lever for the 1-of-3 latch (V, A, ohms).
Spring gets trashed because you have to come in parallel to the switch when installing the adjacent switch into the metal rail.

Next I tried a piece of scotch tape to compress the spring while putting in the adjacent switch. Spring got smeared again. Shot out 10 times. I am not a Zen Master.

Any suggestions? The gap is only a couple mm and no room to work as it's all switch on either side, and the rail forces things to be tight.


It looks like I have to somehow put the whole 4 bank together including spring-from-hell, then put in the rail and crimp. The end switch is push on/off power so it can go in alone.

I think Alps uses a jig to assemble these all at once, then installs the rail and does the final crimp.

No mention of the spring or lock lever on Alps website or Internet I'm sure you can't purchase them. Weird because these switches are also used on signal generators and audio gear.

[stj]

Re: bench multimeter pushbutton switches

compress the spring with a loop of cotton/nylon?

[redwire]

Re: bench multimeter pushbutton switches

Follow up for anyone repairing these Alps SPUN pushbutton switch banks.

I made a spring compressor out of a back-back strip of tape, and taped down the ends. Installed the adjacent switch and gently cut/slid out the piece of tape.

The spring gets smeared easily and pops out and shoots like crazy. I made a tent around the work area (draped a shirt) and the spring usually hits that. HDD magnet on the bench helps catch it too.
Confirm the spring alignment/operation before soldering in the switch bank.


When converting a push-on/push-off switch to momentary or one-of, you have to disassemble the switch and remove two springs in the top cap.
Momentary/one-of have a super tiny clear plastic plug, to stop dirt getting in with the removed spring (last pic).

Putting the switch back together is also very hard, because one hand is compressing the main spring to install the plunger. I crushed some contacts doing it.
Best to slide the plunger in, instead of putting it on top of the base.

Hope this helps people doing this surgery.