The MCI Saga begins

[Dr ZEE]

What bugs me is this. From the way you put it ("Polar caps block DC voltage. So, it's VERY BAD to put non-polar caps in the place of polar caps, as DC will go to places it shouldn't go") one may conclude that "ability to block DC" of a cpacitor is due to the fact that the capacitor is 'polarized' (another words: to block DC a capacitor must be 'polarized'. Or another words: polarized capasitors block DC, whiule non-polarized capacitors do not block DC). Which simply is not the case.
That's why I wish to know what was the source of the info upon which you have drawn such conclusion, so to see wat the details are and maybe to try to connect the dots, sort of speak.

/respects

 

[MCI2424]

Polar caps exist ONLY because of capacity value of the cap. In the past, non-polar caps could not be made in larger capacity because the size would be way too large. All caps block DC voltages (up to their rating) and today there are many more non-polar caps that can replace the polar variety. Non-polar have the advantage of not drying out like electrolytics and are a great alternative if you can get tha size you need.

 

[Muckelroy]

Well, I appreciate y'alls comments.

We've just gotten analog torque card caps from digikey, to match pretty DAMN CLOSE to the originals. Only difference is the brand name, and very slight tolerance differences.

Another engineer I spoke with said that a great trick to cleaning the molex connectors on this machine's cards is to take a big pink eraser, and have at it on the pins, get all the black oxidation off. THEN douse it w/ concact cleaner to finish the job. Said if that doesn't work after 3-4 tries, time to replace the molex.

Once I finish the torque card caps, I'll clean every transport connector I can find, just like that.

Now I twiddle my thumbs as I wait for the parts to ship

-callie-

 

[Dr ZEE]

Another engineer I spoke ...

-oh, boy.

 

[MCI2424]

Well, I appreciate y'alls comments.

We've just gotten analog torque card caps from digikey, to match pretty DAMN CLOSE to the originals. Only difference is the brand name, and very slight tolerance differences.

Another engineer I spoke with said that a great trick to cleaning the molex connectors on this machine's cards is to take a big pink eraser, and have at it on the pins, get all the black oxidation off. THEN douse it w/ concact cleaner to finish the job. Said if that doesn't work after 3-4 tries, time to replace the molex.

Once I finish the torque card caps, I'll clean every transport connector I can find, just like that.

Now I twiddle my thumbs as I wait for the parts to ship

-callie-

Yep. Erasers work great but are hard to get into the Molex connectors. I use contact cleaner and de-oxit. It will take several cleanings to get the connections shiney again. The De-oxit is great in that it leaves a coating that retards any more oxidation. I did my whole machine and all of it's intermintant problems have gone away for a long time now. Good stuff.

 

[Muckelroy]

-oh, boy.

By another engineer, I meant another old hippie that's been doing this for more than 30 years, and knows what works and what doesn't work.

 

[Muckelroy]

Introspective

I thought I'd bring this old post back from the dead.

Unfortunately I was never able to finish this project, and I probably never will seeing as how I no longer attend the recording school where this MCI is housed.

But I have maintained communication with the engineer that works there, and I have confirmed that the MCI is still sitting in its usual hole, collecting unfortunate dust, but there.

Nobody's touched it since I left it. I contacted the engineer and told him that he had better replace two of the caps that were non-polarized caps with the correct polarized caps on the analog torque board.

Much work still needs to be done, possibly to the power supply. If anything happens to this machine I will be sure to let you guys know.

 

[mshilarious]

Nobody's touched it since I left it. I contacted the engineer and told him that he had better replace two of the caps that were non-polarized caps with the correct polarized caps on the analog torque board.

Why? Didn't you listen to Dr. Zee two years ago? Nonpolar caps can take DC bias either direction; polar caps cannot. Thus, a nonpolar cap should be superior to a polar cap, provided that the capacitance and voltage & temperature ratings are correct.

Other minor errata: a microfarad is uF (really μF). mF is millifarad, which is 1,000 times as large.

Nonpolar caps can dry out; it depends on the type of the cap. Probably that poster was thinking about one of the many types of film caps, which won't dry out. But there are electrolytic caps that are nonpolar--essentially two back-to-back polar electrolytics--those can dry out in time just like regular ol' polar electrolytics.