Low Output & Arcing on a Fisher 800C

[angelaudio]

I brought the 800C up slowly on a Variac today but when I got it to 117V I noticed that something underneath starting to arc. There was very low output out of both channels before I noticed the arc. I turned it off immediately but did notice a little smoke in this area where the arcing was taking place:


Here’s a zoomed out shot of the area where this took place:


After flipping the chassis I identified the part that was arcing as 455 I.F.


This unit is all original and has not been recapped so I’m hoping that some faulty caps are the culprits but which cap or caps could be the culprit for causing the arc in the IF module? Could bad caps also be the cause of the low output?

 

[larryderouin]

Resolder that joint, very possibly it's cracked or a cold solder joint, causing an intermittent. And make sure it's not overly close fitting on the leads.
455kHz I.F. is for the AM Band.
10.7mHz is for FM Band.

Let's start over again. Your Post is somewhat analogous to driving to a Dealer and telling the service adviser "It's broke, fix it" and literally walking away. He has no information as to what it's doing and you end up paying thru the nose for days of diagnostics because they don't know what's wrong with it. The smoke in the IF area is not a cause, it's an effect of a different problem. Same thing with the 800c. Specifics help greatly and gets everyone basically on the same freeway, running in the same direction. As we Dig deeper, and get more details, the pack tightens up, and consensus builds.

Remember the 5W's from Elementary school english?
Who; 800c
What: smoke, low output from speakers (secondary right now)
Where: Near the AM IF Stack
When: While starting up unit on Variac
Why: ??
and finally HOW. Unknown but inspection with magnifier may sus out the problem.


Then we have the specific details?!
1.)When you powered up the 800c, what was the SOURCE SELECTOR set to??? AM? FM? Tape Head? Phono? AUX?
2.)Was the Tape Monitor Switch ON or OFF? If ON was a source connected and playing?
3.)Tone control positions?
4.)Loudness Button ON or OFF?

Don't think the specific details will help with the smoke problem. But they can help with diagnosis of the low output. The 800c is pushing 60 years old right now. It's still in original condition. You want it to run.

Do you: Go for total rebuild or just enough to get it running reliably? In the Long run a total rebuild is cheaper. One shot in a shop, and it's good for another 20-30 years (minus consumables ; i.e. Tubes). Or do just enough now to get it running pretty good. It may last or it may break down in 2 days, 2 weeks, 2 months or 5 years. And could conceivably cost 90% of a total rebuild in the 1st place. If you plan on keeping it for a long time, I would strongly suggest you do a complete rebuild.

Have you tested any of the tubes for weak or dead sections. Cleaned anything (pots, switches, tube sockets,etc)???.

Make yourself a DBT and get a 150W incandescent bulb. Until you get this receiver sorted out and fully functioning I would suggest using the DBT. Voltages WILL be lower (as expected.), but if a short occurs the bulb will absorb most of it as it lighting up bright.

In the meantime, list operating conditions at the time of the arcing and we can go from there.

 

[angelaudio]

Thank you Larry, I’ll provide more specifics.

The unit is in the 50,000 serial number range.

The unit was set to AUX
Tape monitor off
Ipod was being played through the AUX
Tone controls both bass and treble were set to flat 12 o’clock.
Loudness Off

I want to get it running pretty good for now so I can have a listen to it and decide whether I like it enough to keep it at which point if I do I’ll just go for the total rebuild.

I’ve only tested the 12AX7’s because my Heathkit TC-2 doesn’t have the ability to test the 7591’s or some of the other am/fm tubes.

Pots and switches have been cleaned. Two rounds of Deoxit D5 on them and scrubbed with a tiny plastic wire brush. Tube sockets have not been cleaned.

I’ll get the DBT built this week. Looking to make a trip to Home Depot today possibly.

 

[angelaudio]

By the way Larry great call on resoldering the 455KC IF transformer. I did it and their isn’t arcing anymore. Still not pulling in AM but FM is working great.

 

[angelaudio]

By the way @larryderouin you’ll have to excuse my blind enthusiasm. I’m just getting into repair and diagnosis of these beautiful old machines and I tend to overlook how complex and intricate they truly are. I get caught up in wanting to hear it and end up getting ahead of myself. I’m sure you know the feeling, but I’m trying to be more patient and pragmatic about the whole process.

 

[larryderouin]

LOL BTDT! Once you get zapped that enthusiasm gets chopped down a little. Nothing like a T.V. Hi-Voltage flyback transformer on a Sears 19" B&W from 1961, nailing you in the arm and throwing you 8' into a wall, and your dad laughing his a** off while you're shaking the tweeting bird and shooting stars from your brain. I reached around to get a tube to test it and got nailed. 15Kv. When I regained my senses and made sure my shorts were dry and intact, I told Dad he could test his tube from then on. I didn't touch another piece of equipment inside until I ws in my late 50's. Oh, I was 8 yrs old in 1963 when I got nailed. Got a few tickles in the past few years, but nothing like that 15kv flyback.

 

[angelaudio]

LOL BTDT! Once you get zapped that enthusiasm gets chopped down a little. Nothing like a T.V. Hi-Voltage flyback transformer on a Sears 19" B&W from 1961, nailing you in the arm and throwing you 8' into a wall, and your dad laughing his a** off while you're shaking the tweeting bird and shooting stars from your brain. I reached around to get a tube to test it and got nailed. 15Kv. When I regained my senses and made sure my shorts were dry and intact, I told Dad he could test his tube from then on. I didn't touch another piece of equipment inside until I ws in my late 50's. Oh, I was 8 yrs old in 1963 when I got nailed. Got a few tickles in the past few years, but nothing like that 15kv flyback.

Ouch! I’ll stay far away from tube TV’s. Took you 42 years to get back into repairing some electronics, that 15kv left a lasting impression

 

[larryderouin]

Yeah it did. I don't mess with spark plug wires either unless the car is turned off.

 

[fred soop]

I once had a TV (probably 21 inch) with a metal picture tube. The bell was painted red. Sometime later, I was working on an intermittent problem for an elderly lady. Thinking that all metal tubes would be painted red, I was reaching in and wiggling some of the suspect tubes when there was a blue flash from the top of my hand to the picture tube. The small tube I was wiggling ended up against the wall behind me and the customer lady was more scared than I was. Eventually got the problem fixed.