[sci.electronics] capacitor question

rschofie@silver.bacs.indiana.edu (04/20/89)

Hi,

  I am an electronics hobbiest, and recently deceided to try and save a
little money by repairing my broken Commodore disk drive myself. One of the
parts I replaced was a 16v, 47 microfarad capacitor. I replaced it with a
35v, 47 microfarad capacitor. Well, now the drive works again with one little
annoying problem. The drive has to "warm up" for about a minute, and then I
reset the computer and everything is fine. Prior to this warm up, the drive
just spins and the read/write LED blinks. So....

Question: Is it possible that due to the higher voltage of the replacement
          capacitor, the circuit has to build up capacitance (or whatever)
          for it to work, or is the problem with something else?

  Remember I'm just a hobbiest, but I think the capacitor is part of the
power supply circuit. I also replaced a diode, and two other capacitors,
but I got exact replacements for them.

  Any comments on this would be greatly appreciated. Thanks in advance.

                                          Robert Schofield


	{pur-ee,ihnp4!inuxc,rutgers,pyramid}!iuvax!silver!rschofie
	rschofie@silver.bacs.indiana.edu (192.12.206.2)
	rschofie@iubacs.bitnet (forwarded)

wiz@xroads.UUCP (Mike Carter) (04/22/89)

 
Rob;
 
Sounds like there's two possibilities here. Maybe a third but we'll cover
that last.
(1) The capacitor you took out of the 1541, is it an electrolytic >?< If
    it isn't and you replaced it with an electrolytic that will cause your
    problem right there. 47 uF ? or .47uF ? If it's .47uF its most
    likely to be a Vcc to ground spike/noise eliminator.
 
(2) Check around where you removed the cap. Lift some leads on a few
     resistors..even if they look good. Check for a 10% value to what
    they should be. SOme resistors wont actually FRY open completely, they
    will increase their resistance by sometimes a Mega Ohm or two.
 
(3) Try resetting right after the power is applied to both the computer
    and the disk drive. Remove the serial cable from the back of the
    computer from the drive and power it up separately. DOes it do
    the same thing? If it doesn't, chances are, the UART in the
    '64 has problems or the HEX buffers on the channel itself.
 
(4) Have a fellow '64 owner bring over their drive and attempt to isolate
    wether its the computer or the drive or both.
 
	Good luck.
 
-- 
=============================================================================
= Mike Carter  N7GYX, Phoenix AZ| Q: Why did the Chicken cross the road  ?  =
= hplabs!hp-sdd!crash!xroads!wiz| A: To ESCape the Main Menu .              =
=============================================================================

monopoli@maxzilla.Encore.COM (Luke Monopoli - Manufacturing) (05/03/89)

>it to be damaged. At low voltage circuit it'll operate exactly the same way
>a lower voltage one with the same capacitance would. (In case voltage, in your
>case 17 V, will not be exeeded). Your trouble is elsewhere!  :-(
>

Yea, Its a cold solder joint. Ah isnt it nice to take wild shots at other
peoples projects:)
>If you're feeling good don't worry - You'll get over it!    :-)
Really I hope it helps-check the solder joints they may be cold and when they 
heat up and expand they make contact.

Luke Monopoli 

Encore TE