Vintage HiFi Audio Forum

Repair / Help Forum => Repair / Help => Topic started by: ESM on April 05, 2014, 01:51:29 PM

Title: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: ESM on April 05, 2014, 01:51:29 PM

 ??? ??? ???

So i was doing some wire cleanup behind the entertainment center and got a shock from the Kimber rca cable coming from the Aux "input" on my fisher 500b. When i touch either the L/R rca cable end then with the same hand touch the chassis of my HT receiver (ground) i get a light shock.

So i got the DMM out and i am registering 40-60v ac. both L/R. mind you the fisher is plugged into a monster HTS 3600 MKII ( hummin like an asia hooker, but thats another problem all together) but the fisher is turned off.

What i've done so far :
1.remove the power plug from the Fisher to the MKII which was plugged into the slot marked "Spare". no voltage present
2. plugged the fisher into the outlet marked "cd" , voltage present at neg terminal on rca cables.
3. plugged the fisher direct into the wall, voltage present at neg terminal on rca cables.

(mind you all of this was done with the Fisher turned off..)


what the heck is going on ? ? anybody ?? i am really hopping this is an I-D-10-T error on my part, a simple home brew fix would be great...
I will take suggestions on the MKII hummer if you have any..( aside from getting a Furman IT that is)

Thanks in advance.

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: ESM on April 05, 2014, 02:00:32 PM

Forgot to state my concerns on this matter :

1.that it is passing voltage in the off position, doesn't seem the slightest bit normal..
2.passing this v40-60v into my HT aux output, cant be healthy electrically speaking..
3.possible damage to my beloved fisher (existing, or worsen) if left unchecked (this was inspected and brought up to snuff by VHF 2-3 yrs ago.)

I love that Fisher, and i want it to continue to a long and healthy life.
It is currently unplugged and not happy with me..

 Thanks.

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: schwarcw on April 05, 2014, 02:38:12 PM

ESM, the 500b is an exceptional piece of equipment.  Has it been recapped, resistor values checked and solder joints refreshed?  I would seriously consider having that done.

My Fisher X-1000 was a console pull that I've had rebuilt and put into a custom cabinet.  I use it daily in my home office. 

Fisher gear rocks!

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: Dicky on April 05, 2014, 02:56:26 PM

All with power turned off?  Should be easier to trace on a schematic id hope

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: bmwr75 on April 05, 2014, 05:41:18 PM

Is there a "death" cap on on side of the 120V AC input?  If yes and this cap this has gone bad (shorted to ground) it can put AC on the chassis.  These caps were suppose to reduce RF noise IIRC.

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: SunnyDaze on April 05, 2014, 06:01:12 PM

Along the lines of what bmwr75 said, you may want to check the voltage between your chassis ground an an AC ground. 

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: Dicky on April 05, 2014, 06:06:51 PM

The 820k resistor in this picture looks like a good suspect, but I've been wrong twice this week.

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: mbskeam on April 05, 2014, 06:21:27 PM

also look at the cap.
if its leaking ac goes to ground

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: SunnyDaze on April 05, 2014, 06:27:23 PM

Quote from: mbskeam on April 05, 2014, 06:21:27 PM

also look at the cap.
if its leaking ac goes to ground

Hear, here!

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: Dicky on April 05, 2014, 06:28:12 PM

Quote from: mbskeam on April 05, 2014, 06:21:27 PM

also look at the cap.
if its leaking ac goes to ground

See, told you I could be wrong.  I have a cap if you dont want to go all the way to the shop.

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: SunnyDaze on April 05, 2014, 06:29:21 PM

Go see Dicky. He'll help you pop a cap in that ass.  >:D

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: bmwr75 on April 05, 2014, 09:44:32 PM

On the schematic, C92 ,01uF is a "death" cap.  If it has failed, AC voltage may be on the chassis.  Just cut out the cap and see of the problem goes away.

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: ESM on April 06, 2014, 01:52:28 PM

http://oldtech.net/Fisher/500B/schem1.gif (http://oldtech.net/Fisher/500B/schem1.gif)

excellent, thanks guys. wish me luck..

Title: Re: Fisher 500b : voltage output on aux input ?? 40v-60v AC
Post by: schwarcw on April 06, 2014, 07:25:14 PM

Good luck!  Don't smoke that 500b or yourself!