Sound Technology 1700B switch cleaning

T

TerryS

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I have a Sound Technology 1700B that I purchased about a year ago. After a complete alignment, it is working pretty well, except that if I don't use it for a couple of months, the switches (mainly the group with Distortion, Set Level, dBm) gets very intermittent. It takes a lot of messing with them to get them to work.
I have read here that I can safely ignore the "Don't ever spray cleaner on these switches" warning labels in the unit, so I plan to go in and give them a good cleaning with Deoxit and follow up with Faderlube. Just getting the unit apart far enough to do a thorough switch cleaning is going to be quite a bit of work. I managed to get the IM Analyzer board out last night and get a good look at the switches. In the past (on cassette decks and such) I have gotten the best results by actually disassembling the switch to clean it really well. If I didn't, it was a crap shoot as to whether it would work or not when I reassembled the unit. Usually, it would be better, but not quite great if I cleaned the switches without disassembling them. But I don't see how the switches used in the 1700B come apart (if indeed they can be disassembled without destroying them). Is it worth de-soldering the switches off the PCBs? What are the odds of doing that without destroying the PCB? They look like fairly cheap PCBs, the kind that are easily damaged, and the switches are all ganged together, so many of them have to come out at the same time. It looks pretty hopeless.

Can anyone offer any suggestions on how best to get these switches cleaned well? Given the amount of work required to disassemble the unit far enough to clean the switches, I'd really like to spend the extra time to get them right the first try.

Terry
 
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Yeah, it'll be pretty time consuming whatever path you take.

There's a couple of tough hurdles.

1. The switches are set up as floors and are stacked.
2. there's switches pushing into other switches.

... but you already knew all of this.

For this, I'd definitely invest in a GOOD desoldering tool. I can personally recommend the Hakko 808. The boards are double sided and the switch contacts will rob the heat if you're trying to use a desoldering braid.

I would take some close-up pictures, note wire numbers and cable dress.

That's if you go "all in". You can try to rest it on it's back panel, remove the white button caps and try to shoot DeOxit down the shafts, but that won't make it to the rear pushed switches and you'll still have the access issue to the middle layers pushed switches.

If you go "all in", then you might want to use some FaderLube too, to have that smoother pushbutton feel.

Cool, you have one with the IM option.
 
Jon,
Thanks for the advice. I'm probably "all in" or at least mostly. The Frequency buttons all seem fine for now. It is mainly the Function group that is giving me a bunch of trouble. But maybe it makes sense to do all of them since it is such a job to get into it.

Is it best to clean with Deoxit, and finish off with Faderlube?

Terry
 
Well, I got all the boards out (at least all the ones with switches). Quite a job. I took pictures and made lots of notes, so there is at least a small chance I will be able to put it back together.
I ordered the Hakko 808 desoldering tool, and a fresh supply of Deoxit and Faderlube (both the spray and 100% versions).
I dissasembled the level set pot (with the 'CAL' switch) since it has been erratic. I cleaned it and reassembled it, but the slider for the pot is pretty worn. Not much life left in it. I searched for a replacement pot, but the usual (Digi-Key and Mouser) came up blank. It is a panel mount 2k Ohm linear with switch. Any suggestions where to find such a thing?

Terry
 
Hi Terry,

Yes, I would wash/spritz/deoxide with the DeOxit, then finish up with faderlube for long term protection and feel.

The "Cal" pot is on it's last legs? Hmmmm, I haven't been there, done that for that one. Yeah, finding the pot with a switch will be tricky these days.

Can you tell who the manufacturer of the pot is? CTS? Alps? Spectrol? Bourns?

I think it was CTS that had the piggy back switch that attached to the back of their pots, but it required the right shaft to toggle the switch element.
 
It is a Bourns, Type JS. I found something that looks promising here:
http://www.westfloridacomponents.com/P012PD.html
Impossible to know if it is the right switch function (OFF when all the way CCW, On otherwise), but I ordered one and will check it out.
The old one may have years left in it (especially since I cleaned and lubed it), but I just as soon put in a new one if I can find one.

Terry
 
Well, the bad news is the pots I found aren't quite right. They are 2k-Ohm and the switch function is correct, but they are definitely not linear taper. The old one may live for years, so I'll use it if I don't find another one before I reassemble.
The good news is that the Hakko 808 is great. I just removed the first switch. I started with one of the easier ones, the two FILTERS switches. They are the smallest ones (fewest poles) and only two mounted together. It was really easy to remove them, so it looks like even the larger gangs can be done. Thanks for the tip on the Hakko!
The switches are very easy to disassemble once they are removed. Now I just need to come up with a good way to clean them. I'll probably use a strip of paper or similar soaked in Deoxit to buff the contacts clean. Then Faderlube to lubricate them before putting the switch back together. It won't be a quick job, but it should be worth it in the end.

Terry
 
If you cannot find a lin taper pot, so what?

It's just the set level control. It won't have the same "feel", but it will probably get you there. You might just set the input attenuator so that the needle is more to the left. Then, switch the pot out of it's "cal" position (where the log taper pot has the most abrupt R change)and use the most CW portion of the rotation to fine adjust your 0dB set level.

You might want to experiment by kluging it in before taking it all apart.
 
Yep, the thought occured to me also. I have two of the log taper (if that is what they are) in case the original dies. I cleaned and lubed it, so it might be fine. The slider foot is just worn more than half way. That could still mean many years of life left in it. I also found (thanks to the source you pointed me to) some linear taper with switch that look perfect. The web site says they have 25 in stock, and I requested a quote for a couple. I've never dealt with those guys before, so I don't know how they will respond to small orders.

I also put a couple of the push button switches back together after cleaning and the Faderlube just doesn't cut it. It needs something with more lubrication. The push-push switches wouldn't return to the full out position on their own. They both needed a little help to fully extend. So I ordered some of the Fader Grease and another type of grease from the Caig site to see how that works.

Terry
 
Ouch!
State Electronics (Potentiometers.com) is not really interested in supplying low quantities for their pots. This is the quote they supplied:

Qty 2; $125 ea.
Qty 5; $70 ea
Qty 10; $40 ea
Qty 25; $25 ea

Terry
 
Yeah, those obsolete parts brokers have no shame.

When you said that you had requested a quote, I thought to myself, "uh oh".
 
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