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Elka Rhapsody 490 stringer recap PSU only or ALL?
Old 16th January 2019
  #1
Gear Head
Elka Rhapsody 490 stringer recap PSU only or ALL?

Bought this machine for cheap in very good condition a year ago and plan to give it at least new caps for the psu before I even attempt to power it on, as it is from ca 1976 and has an unknown user history.
It is also filled with smaller caps in the circuit, some are also close to rare divide-down chips.
Is fear of having these smaller ones blowing close to these chips rational?

Also, the psu uses 2000uF/50 axial caps which seems to be rare/expensive.
Could I replace them with 2200/50 radial caps?

Thanks for input!
Old 4 weeks ago
  #2
Lives for gear
 
Brian M. Boykin's Avatar
I replace axials with radials all the time if they’ll fit. It’s quite exhausting finding axials anymore. I’ll let someone with more knowledge than mine answer the other questions. I typically do value for value unless someone I trust has given me mods that are tested. I can follow directions, still learning circuit design.

Brian
Old 4 weeks ago
  #3
Lives for gear
 

That unit likely has boards that run on low voltages of 24V or less.

If you're worried, you could probably disconnect the power supply then run its power up slowly on a variac and see if its DC output is steady and free of AC leakage.
beyond that, I'd simply crank the thing up and see how it sounds. I realize older synths sell for high dollars because of the mythology surrounding them but to be honest this one is consists of only two string sounds and you can probably find a gazillion keyboard that can do the same job better for a lot less.

In any case, keyboard run on low voltages and other then possibly the power supply caps getting weak, most techs will tall you to leave it alone unless there are symptoms telling you they need to be replaced. No tech I've met in the past 60 years of being a tech would simply replace caps without a reason.

If you're worried about the values having drifted, spend $10 and buy a meter that can measure capacitance. Then lift the legs of the larger PS caps and read their values. if they are off by more then 20% then they might need replacement. If they don't have dead shorts then its unlikely you'll have issues. Most caps will come back and be reformed by simply running them and allowing their aluminum oxide dielectric barriers to build back up. Of course once the units powered up you can also test the DC voltage and see if its in the ball park. I wouldn't do anything besides normal cleanup unless I hear hum on the line out which indicates AC in the DC supply. I'd make a list and price the parts plus shipping before I dove in and did anything.
Old 4 weeks ago
  #4
Gear Addict
 

If they do need replacing, replacing 2000 uF with 2200 uF won't be a problem. Electrolytic capacitors (particularly older ones) have pretty loose tolerance specifications for their capacity anyhow, something like +50/-20% of nominal value is not atypical. 2200 uF is practically a direct replacement for 2000 uF in a power supply filter capacitor, assuming other parameters are equivalent.
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