Williams Solved Blackout (Williams, 1980) Capacitor question...

[pb1592]

Hi guys,

This question is regarding capacitors on an MPU board (Williams, system 6). The bill of materials states its a "Ceramic, .01mfd, 50V Capacitor" (component C63)...

First off, dumb question, these caps aren't polarized (non-electrolytic), right? I see them on the board (30 of them) but see no marking indicating polarization (they look just like glass cylinder-type zener diodes without the black band).

Second, is it ok to replace the capacitor with another cap of the same voltage but higher mfd rating? (e.g. replace mentioned cap with a .1mfd, 50V)?

I can get .1uf 50V ceramic disc cap from radioshack versus waiting for an online order. Would this be a sufficient replacement cap for this application to replace the cap mentioned above?

Thanks!

 

[Shockman]

Although there are certainly people that would know, unlike me. I have never liked the idea of getting advice on changing parts specs outside a certified expert. I would wait for the replacement part if there was no such shop around.

For example someone might think it is logical to use either a non polarized, or a polarized part as long as a polarized unit is wired correctly. I don't think it's that simple. I also don't think you would find a polarized and non polarized one that did have the same specs.

I would surly not use a part that had different specs printed on them on my own, nor nearly anyone's advice.

Pinball machines are high voltage machines, and damage from incorrect circuitry may not be contained to the problem area.

 

[spalmer]

Although there are certainly people that would know, unlike me. I have never liked the idea of getting advice on changing parts specs outside a certified expert. I would wait for the replacement part if there was no such shop around.

For example someone might think it is logical to use either a non polarized, or a polarized part as long as a polarized unit is wired correctly. I don't think it's that simple. I also don't think you would find a polarized and non polarized one that did have the same specs.

I would surly not use a part that had different specs printed on them on my own, nor nearly anyone's advice.

Pinball machines are high voltage machines, and damage from incorrect circuitry may not be contained to the problem area.

I agree. You are talking about a huge varience compaired to the original specs. Why are you wanting to replace all of these caps? What kind of problem are you having with the board?

 

[pb1592]

Well, i wanted to know mainly because i was having difficulty finding a cap of the specs i needed for a reasonable price. most places required bulk purchasing and i didn't want to spend $20 on a fifty-pack of caps when i only needed one.

I do have a follow up question though... I have found a cap of the exact specs i need. The only problem is the one on the board that i need to replace is a tantalum and the one i found with the same rating is electrolytic. Is it OK to replace a tantalum with an electrolytic as long as the specs are the same and the polarity is correct? note: it is for a Williams System 6 MPU, specifically capacitor C31 (1mfd, 25V). This is a different cap than the one i originally posted a question about.

Also, the problem that i am having in which i am considering a cap replacement is described in full detail in the "Williams system 6 (Blackout) MPU trouble... " thread i created a few weeks back (still no resolution )

Thanks!

-Brian

 

[Shockman]

Again, you are talking about using a polarized part to replace a non-polarized part. These polarized electrolytic ones are meant for DC current, aren't they? Wiki says you would need a DC polarizing bias to use one with AC. I don't know what that is.

Personally I would spend $20 for one, if it was exactly what I needed to get a pinball machine working, but like I said, I could be convinced otherwise, to use something else, that is, but probably not from anyone here.

 

[pb1592]

Yes, but the MPU board uses 5V and 12V DC from the power supply.

 

[mrschultz]

For the original cap you mention going from 0.01 to 0.1 is a 10 fold increase, would be OK on a DC supply line but if it's on a signal line you'll probably end up smoothing out fast signals. And if they are part of an amplifier you could change the gain of the circuit. In other words, get a 0.01 to replace a 0.01.

For the tantalum cap being replace with an electrolytic, if the specs are all the same it will do the same job. Electrolytics usually don't last as long as tantalum ones, so you might need to replace it in a year or 2 while the tantalum would last many years. Electrolytics also make a mess if they leak, but that's pretty rare for modern ones.

Oh, and FYI, tantalum caps usually have the positive side marked, but eletrolytics often have the black line on the negative side... So double check the polarity.

 

[spalmer]

For the tantalum cap being replace with an electrolytic, if the specs are all the same it will do the same job. Electrolytics usually don't last as long as tantalum ones, so you might need to replace it in a year or 2 while the tantalum would last many years. Electrolytics also make a mess if they leak, but that's pretty rare for modern ones.

Tantalum are also more resistant to noise than electrolytic. I am not sure that I would make this substitution on an MPU board. You could wind up wuth strange behavior, (lock ups, etc.) if you had a noise problem. If you can find a tantalum with the same value but higher voltage rating it would work fine.

I am still curious as to you reasoning for changing out all of the caps. Is your MPU board in that bad of shape???

 

[pb1592]

No its not in bad shape... it was working perfect up until a few weeks ago. I described the problem in detail in the thread: "Williams system 6 (Blackout) MPU trouble... ". I've tried several fixes and none have worked so far. One thing that was suggested was to replace C31 as it supposedly tends to fail frequently. Only problem is I can't find a tantalum with those particular ratings (I did, however, find an electrolytic of that rating).

I never had intentions on replacing all of the caps on the board. From what i read about the problem i'm having there are two suspect caps that could be the culprit. First was the Ceramic, .01mfd, 50V Capacitor - which, since my original post, i had found an exact replacement for (but did not correct the problem). Second is the tantalum 1mfd, 25V - which i've only seen electrolytic aluminums with this rating in a reasonable quantity/price.

 

[sleepy]

Again, you are talking about using a polarized part to replace a non-polarized part. These polarized electrolytic ones are meant for DC current, aren't they? Wiki says you would need a DC polarizing bias to use one with AC. I don't know what that is.

AC stands for Alternating Current, alternating from a half cycle of positive current on the positive peak of the AC waveform to a half cycle of negative current on the negative peak of the AC waveform.

Electrolytic capacitors are polarized, meaning one lead is negative and the other is positive, same as the terminals on a battery, so a polarizing DC bias for an AC input means adding a DC voltage of the correct polarity in order to raise or lower the voltage potential of a Sinusoidal AC input or any signal that has a variable polarity to within the positive or the negative polarity of the terminal the input is applied to.
For instance a bilateral AC signal which swings positive to negative peak-to-peak with a 0 volt axis at centerline applied to the negative terminal of an electrolytic capacitor requires an additional negative DC voltage so that the AC input does not rise above 0 volts. If it does rise above 0-/+ volts, say 1+ volts, you run the risk of blowing the electrolytic capacitor same as applying the wrong polarity of voltage to the wrong terminal of a rechargeable battery.

The DC bias is usually done only in regards to electronic monitor circuits for AC generation, and in high power inputs such as high power audio amps.
In general, electrolytics are used for their polar characteristics in power supplies at the rectifier stage (AC to DC conversion stage) owing to their higher power handling and stability against power fluctuations.
They really are "a virtual battery".
The larger electrolytics are where the danger of death from electrocution comes from, in Farads, so don't touch the leads assuming it's exactly like a battery, not before shorting the leads through an insulated conductor (an insulated wire, etc.) in order to discharge the stored charge. It is good practice to Always discharge any capacitor by shorting the leads before you handle it. Do not touch live circuits.

Non-polarized capacitors can be connected in circuit in any direction, but these are usually for low voltage use (audio signals at the pre-amp stage or in low power amps, IF radio circuits, etc.), and where power stability is not critical.

 

[pb1592]

I found a 1mfd 35V tantalum cap... is this a safe substitute for a 1mfd 25V tantalum cap?

 

[spalmer]

That should do the trick nicely. You can go with the higher voltage rating 35v just not lower. Did you get a good look at that interconnecter. These again usually are the source of your lockups on the system 3 thru 7 boards. What kind of shape is the machine in otherwise? I don't know your financial situation or how much you what to put into the machine but you might be chasing a wild goose so to speak.

If you want some top quality repair in the current board I would recommend lockwhenlit. Rob does excellent work but sometimes takes a little while. He runs the pinball show circuit and sometimes gets a little behind. My other recommendation if the cap does not solve your issue with the a rottendog replacement board. I used one of these in a Firepower machinethat I had a while back. Exellent board. It is a combo board that replaces the driver board and mpu. You can check it out here.

http://www.rottendog.us/mpu327.htm

 

[pb1592]

FIXED IT! Turns out it was the PIA at IC18 that was the culprit.

Thanks for all your help though! I appreciate it.

-Brian