Non-Polk Capacitor advice needed ( dbx 118 )
Schurkey
Posts: 2,102
I have a dbx 118 with a defective Root-Mean-Square Detector daughter-board. The unit works perfectly when I snap in the RMS Detector board from a second 118. Therefore the problem is localized to the RMS Detector in the photo below.
I have replaced the dual op-amp "chip", and am about to order each of the five capacitors on this board as soon as I confirm their values. Five-year-old posts on other forums have suggested that the caps are prone to failure. I'd order the 5-transistor array QA1, but Digi-Key doesn't list a CA3046 or CA3146. Closest they have is LM3046, the SOIC equivalent of the DIP-package I need. Bummer.
The caps are labeled with various numbers. These numbers somewhat match up to a non-factory schematic apparently reverse-engineered by a European enthusiast. I have found several errors on this schematic already so I don't have absolute faith in it.
The Real Question: What "units" should I expect to go with the numbers printed on the caps? I can read the numbers, but none of them show what unit--uF, pF, or nF goes with the number value.
C1 vertical brown disc just above horizontal brown disc = ".001" 10%__Schematic says 1nF. Can I believe that? .001uF = 1nF.
C5 horizontal brown disc w/ white leads. = "22" 10%___ Schematic says 22pF. Does that seem reasonable considering that it's physically smaller than C1?
C2, C3 paired red bulbs bottom right = "22" 16 Volt___ Am I nuts? Seems too small to be 22uF. How about 22nF or 22pF? Schematic says "22uF, 35 volt", but my actual caps clearly say 16 volt.
C4 smaller red bulb bottom left = "1" 35 Volt___Again, seems too small to be 1uF. 1nF or 1pF seems more likely to me. Schematic says "1uf, 25 volt" but mine is clearly labeled 35 Volt.
Are these red bulbs "Tantalum" caps? Tantalum caps are known for shorting, and also for packing a lot of capacitance in a small package. Could genuinely be 22uF and 1uF after all--I'm starting to believe this.
I have replaced the dual op-amp "chip", and am about to order each of the five capacitors on this board as soon as I confirm their values. Five-year-old posts on other forums have suggested that the caps are prone to failure. I'd order the 5-transistor array QA1, but Digi-Key doesn't list a CA3046 or CA3146. Closest they have is LM3046, the SOIC equivalent of the DIP-package I need. Bummer.
The caps are labeled with various numbers. These numbers somewhat match up to a non-factory schematic apparently reverse-engineered by a European enthusiast. I have found several errors on this schematic already so I don't have absolute faith in it.
The Real Question: What "units" should I expect to go with the numbers printed on the caps? I can read the numbers, but none of them show what unit--uF, pF, or nF goes with the number value.
C1 vertical brown disc just above horizontal brown disc = ".001" 10%__Schematic says 1nF. Can I believe that? .001uF = 1nF.
C5 horizontal brown disc w/ white leads. = "22" 10%___ Schematic says 22pF. Does that seem reasonable considering that it's physically smaller than C1?
C2, C3 paired red bulbs bottom right = "22" 16 Volt___ Am I nuts? Seems too small to be 22uF. How about 22nF or 22pF? Schematic says "22uF, 35 volt", but my actual caps clearly say 16 volt.
C4 smaller red bulb bottom left = "1" 35 Volt___Again, seems too small to be 1uF. 1nF or 1pF seems more likely to me. Schematic says "1uf, 25 volt" but mine is clearly labeled 35 Volt.
Are these red bulbs "Tantalum" caps? Tantalum caps are known for shorting, and also for packing a lot of capacitance in a small package. Could genuinely be 22uF and 1uF after all--I'm starting to believe this.
Post edited by Schurkey on
Comments
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Yes the red ones are tants.The bigger one could be 2.2 or 22uf.Is there a third digit after the 2 such as 225?
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No. The caps are labeled "22 16V".
Took another look, there's a pair just like them on the main circuit board, and the dbx factory schematic calls them "22uF TANT", so I have my answer on those. I interpolate that the other, smaller red bulb is a 1uF 35 volt.
That just leaves the two ceramic jobs. I'm pretty sure they're 1nF and 22pF.
Took a look at the twin circuit boards for the Voltage-Controlled Amplifiers (VCAs) They've each got a single teeny-tiny ceramic disc capacitor. One of them is labeled "10J ICC"; while on the other circuit board it's labeled "101".
I found a web site that discusses disc capacitor codes. 10J is code for 10pF, with the "J" representing 5% tolerance. This makes no sense because 101 is code for 10pF, plus one more zero at the end--or 100pf.
http://www.solarbotics.net/library/pieces/parts_elect_pass_cap_code.html
I took the chicken way out--I orderd 10pF and 100pF discs, and I'll install whichever the spirit moves me unless I receive Earthly guidance.
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Closing-out an old thread. Capacitors were not the problem, but it didn't hurt to freshen them. Actually, I replaced EVERY cap in the unit.
Installed a CA3046 transistor array, (along with a 14-pin socket) onto the RMS detector, and the unit is back in business.
