[AMRadio] Suggestions for restoring a DX-100

[George Pritchard]

Reforming caps, or verifying leakage on them is easy if you have one of
those older 0-400 VDC high voltage variable supplies (heathkits $10 at
fests). I used it to verify leakage on "New Old Stock" caps and noticed very
high leakage, >10 mA at only 100 Volts! I'd leave them at 100 volts until
leakage dropped to < 1 mA... then go up slowly to 200 volts, and wait again.
Repeat the process untill you get to 400 volts on the 450 volt rated caps
with less than 1 mA current. I did this for the replacement caps on my
DX-100. Guess what... They only lasted two weeks and shorted again anyway! I
ended up with big oil types mounted where the HV 5U4s used to be before I
solid-stated the supply. The oils will never fail. BTW... I used the
Heathkit supply to verify the shorted capacitors in the first place. It
saves fuses and possible the transformer!!! Good luck.
George AB2KC

-----Original Message-----
From: amradio-admin at mailman.qth.net
[mailto:amradio-admin at mailman.qth.net]On Behalf Of Bill Smith
Sent: Wednesday, April 03, 2002 2:52 PM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] Suggestions for restoring a DX-100


Don't turn it on and expect the electrolytics to survive the shock.  Bring
up line voltage slowly with a variac, or light-bulbs in series with the
power line.

Start with about 60 volts.  Just enough to light the filaments in the
rectifier and feed voltage into the power supply.  Ramp it up slowly from
there, over the next several minutes.  It should begin to operate at about
90 volts.  Play it at 110 volts for a while (ten or so minutes) before
giving it the full gas, watching for trouble.

If you go through this simple procedure, you may recover all the
electrolytics.  If you don't, you'll be sure to replace at least one can.
Look at the circuit to see how B+ is switched, and see if there is some way
to reform any cans that are switched on only during transmit.

Unfortunately, there is no recourse to tubular paper caps, they become leaky
over time and will likely need replacement.  They may seem "ok" when you
first use the equipment, but will quickly degrade with use.

73 de Bill, AB6MT
billsmith at ispwest.com


----- Original Message -----
From: "russ dworakowski" <wb3fau at hotmail.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, April 03, 2002 11:35 AM
Subject: Re: [AMRadio] Suggestions for restoring a DX-100


> John,  what to do   with  your DX-100 has a lot to do with how  it  has
been
> stored.  Transformers  are  not a common  problem in the  DX 100 as  they
> are the potted type  and  less subject  to moisture damage.
> Replacement of  power supply  electrolytiics  is  most  common problem.
> These rigs sit around  not  in use  for  long  periods causes  the
> capacitors to go bad.  There are a  few in the   audio  section  to check
as
> well.  Good  luck and  have  fun!   Russ
>
>
> >From: "john_walker_beasley" <jbeasley at earthlink.net>
> >Reply-To: amradio at mailman.qth.net
> >To: "AM Radio Reflector" <amradio at mailman.qth.net>
> >Subject: [AMRadio] Suggestions for restoring a DX-100
> >Date: Sun, 24 Mar 2002 11:43:38 -0600
> >
> >Gentlemen:
> >
> >     I have a DX-100 and I am looking for any tips or advice
> >before I begin working on it.  It is in good cosmetic condition
> >and the quality of the soldering looks good.
> >
> >     I am familiar with the replacement of electrolytics, however,
> >my expertise with aging components pretty much stops here.
> >
> >     What I  am mostly concerned about is trying to avoid the
> >problems some people talk of such as losing mod transformers
> >from the failure of other aging components.
> >
> >     What precautions should I be taking? What other components
> >should be scrutinized. ?
> >
> >     Any suggestions or links that may be good reading on this
> >topic ?
> >
> >     Thank You
> >
> >     --... ...--
> >     John WAØSTX
> >
> >
> >
> >
> >
> >
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