Ensoniq SQ2 trouble shooting advice needed

[Jesse Pearson]

Anybody familiar with these little yellow components on the main board. I thought they were ceramic capacitors because they have a .i.e. "C89" silk screened next to them like the electrolytic's do on the main board, but I can't find anything on them at all so far. They have a code but it does nothing when I google it. I think ceramic caps have a special code system that I just stumbled across today on the net and down loaded, but it doesn't seem to match. I need some info on these yellow components so I can test and replace them if needed. My ESR meter works on some of them and others it gives me nothing, like I don't have any probes on them? I haven't even seen anything on the net that looks like them yet. Maybe I'm calling them the wrong name? Ensoniq was using them on their boards 24 years ago. Enzo and Dude, you guys probable had to deal with these over the years, what do you remember about them? Thanks...

[Enzo]

They are caps, I don't recall values, and I don;t recall ever seeing a bad one.

Usually printed on them. The green ones Peavey uses look like resistors, the color code reads in picofarads. If I recall these just have a number printed on instead of color stripes, but reads the same, so 222 would be 2200pf.

[The Dude]

Caps do short on occasion, but not that often. I'd be more apt to believe you are looking for a solid state device that's shorted or leaky loading down your supply. Is anything getting hot when power is applied?

[Jesse Pearson]

Thanks guys...Yes Dude, there is a multiplexer that is too hot to touch located at U9 on the main board (MC14051B). It's temp under power on the board is 95c. The data sheet states the Temperature Derating: Plastic "P and D/Dw" Packages - 7.0 mW/C. from 65.C to 125.C. Don't have enough exsperience to know exactly how to interpret these values yet. I ordered some replacements and received them already from E-Bay, just in case I need to desolder the 16 pins to replace it lol. Under power it shows pin 8 Vss gnd to pin 16 Vdd +v to have 5 volts. I tested the output/input pins in circuit without power using the diode checker and got good voltage drops except for pin 3, which is the common output/input pin. It showed a voltage drop of .100 volts? Not sure what that exactly means. I do know excessive heat is bad however. Those little yellow caps have really got me stumped. I haven't as of yet even found one pic of them on the net much less a data sheet.

[MarkusBass]

I would leave those yellow cap. They are still used by many manufacturers (eg. Ampeg) and can be purchased without any problems. Regarding the multiplexer, you can cut the pins and desolder each pin separetely. Or, use Chip-Quick.

[Jesse Pearson]

Thanks Markusbass for the advice. Could you please give me a link for buying some of those caps if possible, because I can't seem to find one. Since I'm so in the dark on them, I want to know how to test them correctly (what I'm doing is getting inconsistent results) and where to buy them as well. I would really appreciate a data sheet on them to really understand them if I could find one. Knowing the right code for the pin out package would probable teach me a lot. I don't know why I'm having such a hard time on finding any info on these particular parts. I guess I'm still just developing my electronics vocabulary and parts finding skills at this point. I understand the picofarads number system for ceramic caps now, but I still can't find these little yellow caps anywhere.

[MarkusBass]

I'm currently on holidays so cannot give you much details. I also don't know what is your location. If this is USA, they can be purchased from Amazon, or Newark. Search for "Aximax series axial ceramic capacitor" in google and you will find everything , including datasheet.

[Enzo]

I really doubt they are bad, but they are just common little caps. You might not find the exact part they used 25 years ago, but the electricity doesn;t care what color they are. Mouser or similar suppliers would surely have them.

[The Dude]

I wouldn't obsess on the caps. It's unlikely any are bad.

[Jesse Pearson]

I was having a hard time finding these caps because I wasn't using the right terminology nor did I know how to read the values on them. I went to Amplifier Parts web page and looked up their list of capacitors for sell, oh my gosh, had no idea how many different types there were beyond the electrolytic and ceramic disk types. I was able to pick up on the key word "Axial" and I finally found a ceramic cap in Pico-farads that was a visual match with a Data Sheet made by KEMET. https://www.alliedelec.com/kemet-c41...g5ta/70094990/

Thanks Markusbass, those were the magic words (Aximax series axial ceramic capacitor).

[g1]

Generally when caps like that cause loss of supply voltage (due to failure) they are from the supply line to ground and acting as IC decouplers. In those cases (failed) they are usually quite low resistance which you can pick up with a resistance check using you regular meter.
However, those bullet shaped yellow caps with the + markings are tantalum caps which are more likely to fail. Again, a resistance check will show a bad one to have a low resistance (say, under 100 ohms).
That hot chip does not sound good, but I'm thinking it runs off 5V rail so may not be the cause of the supply issue. As far as I know you are looking for something pulling down the minus 18Vrail, which would not be used for the 14051.

[Enzo]

The 4051 is an analog switch - a MUX. It will handle up to +20 power voltage.

The IC bypass caps tend to be right at the ends of each chip on this board. The row of them like in the earlier photo would be a row of inputs to the IC and the caps are ther to prevent spikes and such from false triggering.

[Jesse Pearson]

GI, that big tantalum cap has .005 ohms in circuit. I guess I should pull one leg out of circuit to see if it still has the same reading. There are a handful of failed aximal ceramic PF caps on this board. Some just have low DC resistance and are in the danger zone. They are going to get replaced just to make the board perform better.

Enzo, thanks for that info. I was wondering what job all those little yellow aximal PF caps had, good to know.

[MarkusBass]

I wonder how you check the axial capacitors. In circuit? I haven't seen such a capacitor failed, although it is possible. Hard to believe that you have a handful of failed capacitors.

[Enzo]

Like any other cap in a circuit. Check it in place, if it isn't shorted there, it won;t be shorted elsewhere or loose. If it checks as shorted, then lift it and recheck.

Those have an extremely low failure rate.