Re: FG 504 problems

Colin Herbert

Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?


-----Original Message-----
From: [] On Behalf Of Dan G
Sent: 08 August 2020 01:15
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


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