FM-100-C Resto-Pak Snafu Averted(MPX methinks)

IMTubeHead

OsteoFisheritis
Hi everyone,
I have been pulling my hair out for the past week after installing components from Fisher Doc's Resto-Pak. I should have come here first and I would have then known NOT TO MESS with anything related to the MPX circuit or PC board components....but I didn't know about this Fisher Forum until I started looking for help here(I'm already a member since last year) My baby is working now, but I want to share my grief with you(LOL) :p
So I've had this FM-100-C for a couple of years now, and it's been working flawlessly, but in the back of my mind I figured that at least most or all of the electrolytic caps would need to be replaced at some point, so when I was on our favorite auction site looking at Fishers I saw the Resto-Pak, and I checked out the Fisher Doc's website, so I figured all would be good, as he appears to be a reputable guy. So I get the Pak along with a owners manual and schematics, and instructions. Kit was missing one capacitor and a bridge rectifier for starters, so I contacted the Doc and he said he would review the pak and send me the missing parts. Still no parts after 2 weeks.
The first mistake I made was not powering up with a Dim Bulb Tester after installing each component to make sure everything was going correctly(I read about the dim bulb tester here) I had studied the schematic and the insides of my unit for about 1 week to familiarize myself with the layout since I'm fairly green working with point to point so I drilled myself tracing circuits and trying to figure out what did what and using the schematic. I checked and double checked each component that I replaced, and I took my sweet time. After I finished my next step was to plug 'er in and watch 'er smoke :p This is always the scariest part for me!! Really! I know I double checked each component but there's always that possibility that I screwed something up. So I plugged it in while it was out on my balcony with the sliding glass door closed to protect me(LOL) NO smoke, the tubes all lit up, so I turned it off, brought her in and hooked it up and all I got was white noise!! NO MUSIC!! Oh, I was so let down and frustrated after taking my time and all. I set the tuner aside and didn't touch it for almost a week. Then I started searching for Fisher help and I found it here! Not for my 100-C, but I read something in one of the stickies about Resto-paks and not to replace any of the components on the MPX board...that got me thinking...(glad that I didn't throw the old caps away!!) So last night I removed the new caps from the MPX board and put the old ones back in. Then I plugged it in and STILL it didn't work...just white noise. Now I'm scratching my head. So I looked at the schematic at the MPX board and traced backwards to see if there was a new cap in the circuit path...Sure enough, there was(C38, a 8mF, 50v electrolytic), which was the very first cap I replaced when I started the project...and the only one I threw away in the recycle bag...so I had to dig through the recycles until I found it!! Put it in and fired up the tuner again...this time she was SINGING TO ME!! I breathed a sigh of relief!! God I was SO HAPPY that this group helped me troubleshoot my problem by talking about not changing anything on the MPX board(or right before it, it appears) The part of the circuit, it appears to me, is the final RC filter before the FM signal goes to the MPX PC board(see attached schematic). The main reason that I'm telling you all of this is because I really don't know what happened. I have an idea, but I'm not sure 100%. I think that by changing the caps on the PC board and the final RC circuit before the MPX board I somehow threw out the FM alignment...but that's just a guess.
I think AK is a very cool place, and I've read a lot here and I can speak from this experience that there's a WEALTH of knowledge here. Thank you SO MUCH!! I'm listening to Joe Cocker on "The Drive-WDRV in Chicago" right now, and man does my Fisher sound SAWEET!! Awesome them Fishers is :p

John
 
Here's the scans of the schematics and Resto-Pak caps to replace...

John
 

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Sounds like you installed the replacement for C38 backwards, which will cause loss of FM signal.

glad you got it figured out.

Larry
 
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