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 Post subject: Dumont RA170
PostPosted: Apr Wed 04, 2012 1:54 am 
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I recently found this gorgeous TV at the tail end of an estate sale. I had no idea what i was getting myself into, but he CRT lit up when I plugged it in, so I bought it. I'm totally in love with the case and the gorgeous sound that comes out of the speaker buried in there.

I hooked it up to a VCR with an old school two-prong adapter and was pleased to see rolling picture. The contrast looks good and the image looks to be pretty sharp, but I cannot stop the rolling. I can't see any horizontal adjustment knob anywhere, at least not accessible from the exterior of the case. Anybody familiar with these "telesets". I'm grateful for any help you an suggest.


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 Post subject: Re: Dumont RA170
PostPosted: Apr Wed 04, 2012 2:13 am 
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Try the "vertical hold" control.

.


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 Post subject: Re: Dumont RA170
PostPosted: Apr Wed 04, 2012 7:43 am 
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Does that center panel flip down?
Often the lesser used controls are behind those.

Rolling of a otherwise coherent picture would indicate a Vertical Hold issue, a bunch of slanted lines would be Horizontal.

Regardless of whether it works or not now it's been around since the mid 1950's and really needs to be electronically restored before it can be used reliably, unless it already has been by the previous owner.


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 Post subject: Re: Dumont RA170
PostPosted: Apr Fri 06, 2012 4:34 am 
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Quote:
Does that center panel flip down?
I had no idea! That's like some James Bond action there. The whole Dumont badge flips down like the license plate over a gas cap on a 1960's car. love it! Now that we';re all digital in Minneapolis, I have to hook a box up to it to see what we get, but I'm stoked.

Thanks Eric H!

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 Post subject: Re: Dumont RA170
PostPosted: Apr Fri 06, 2012 12:41 pm 
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Try a VCR or a DVD player hooked to a rf modulator. Many places still have analog cable also.


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 Post subject: It's ALIVE !!!
PostPosted: Apr Sun 29, 2012 7:22 pm 
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Thanks for the help, everybody! This Teleset is BACK ON THE AIR! So I am kind of a dork, but I would rather watch the Dick Van Dyke Show on this beauty than almost anything on TV these days.

http://www.youtube.com/watch?v=lj-LvkGW26Y

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 Post subject: Re: Dumont RA170
PostPosted: Apr Sun 29, 2012 8:18 pm 
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as well as that works I am guessing its been restored already, nice find. Still would not hurt to have someone that knows what they are doing check it out to at least see if the old paper caps have been done, but I would guess it must have been. In the mean time just don't leave it on un attended, this is pretty much true about ANY vintage electronics.


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 Post subject: Re: Dumont RA170
PostPosted: Apr Sun 29, 2012 8:40 pm 
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How do i go about testing the tubes? Anybody familiar with the vintage TV scene in Minnesota?

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 Post subject: Re: Dumont RA170
PostPosted: Apr Sun 29, 2012 9:33 pm 
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Either buy a tube tester or know someone who has one. There is a repair shop on 119th and University, up in Blaine, that can help for sure. They advertise on Craigslist. I've been there.

There are a few guys in your area. I'm up by St. Cloud.


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 Post subject: Re: Dumont RA170
PostPosted: Apr Sun 29, 2012 9:41 pm 
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toyfreaks wrote:
How do i go about testing the tubes? Anybody familiar with the vintage TV scene in Minnesota?

Join the Northland Antique Radio Club, they have many people interested in old TVs that can probably assist you. They have a big meet coming up in just 3 weeks. Should be plenty of tube testers for sale there.

http://www.northlandantiqueradioclub.com/


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 Post subject: Re: Dumont RA170
PostPosted: Apr Sun 29, 2012 11:18 pm 
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A TV which works that well isn't likely to have any serious problems with bad tubes. If you want to test 'em anyway, bring them to the swap meet and ask someone with a tester if you can use it for a few minutes.

Buying a tube tester seems pretty low priority unless you plan to get seriously involved with restoring tube radios & TVs. If you want to spend money on this TV, pay someone to check it out and replace the electrolytic capacitors in the power supply, so you can play it without worrying that it may go up in smoke any moment. Unlike tubes, capacitors can and do deteriorate simply from sitting around.

Just my $0.02.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html


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 Post subject: Re: Dumont RA170
PostPosted: May Tue 01, 2012 7:50 pm 
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There is a sharp bend in the top of the TV picture. It seemed to be related to the Vertical Linearity control, but like the amount of correction needed was beyond the top of the dial. It got lots worse if I turned it left, and just started getting better at the far right.

philsoldradios wrote:
replace the electrolytic capacitors in the power supply, so you can play it without worrying that it may go up in smoke


Thanks for the safety tip, Phil. It did make a loud cracking noise a couple times while it was warming up, followed by a whiff of ozone. That startled me a bit, but not enough to keep me from going back in the house to take a phone call. Eventually I thought "Ya know, how certain am I that thing's not ON FIRE right now?"

Are the capacitors something I can remove, or are they connected to the board? I got the TV for a song, so I'm willing to put up to $100 into it. I've spent more than that on stupid new things that never dd work very well and i regretted ever buying.

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 Post subject: Re: Dumont RA170
PostPosted: May Tue 01, 2012 9:13 pm 
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Vertical Linearity has more to do with the proper scanning, you need a good round test pattern to really get it right. the hook in the top could be a sync issue, maybe agc, maybe a defect in the vert generating a powerful spike. adjusting the linearity control just stretches the top of the screen out, or compressing the effect. the caps are not a plug in part like tubes, you need to have some soldering skill. Better left to someone that has some tech repair experience.


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 Post subject: Re: Dumont RA170
PostPosted: May Tue 01, 2012 10:03 pm 
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DaveM wrote:
the hook in the top could be a sync issue, maybe agc...


Yay! I found a copy of TV Repair For Beginners by Homer L Davidson on Google Books. The way they describe sync failure sounds very similar to my problem.

"Any malfunctions in the sync section are certain to produce... either an up or down rolling of picture or tearing in a horizontal direction."

It was also very difficult to stop vertical roll on this TV, and there is a buzzing in the sound signal when the screen shows bright whites.

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 Post subject: Re: Dumont RA170
PostPosted: May Wed 02, 2012 12:09 am 
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Vertical rolling can also be caused by problems in the vertical circuits. Horizontal tearing can also be caused by problems in the horizontal circuits. It is common for old TVs to have problems in both vertical and horizontal sections.

Buzzing on high-contrast scenes is also common in old TVs. Recapping and aligning the audio section may reduce it, some times not so much.

If you count the number of paper and electrolytic capacitors in this TV, that approximates the number of potential problems that it has. All of them (probably three or four dozen parts) are suspect, if not already funky. A professional restorer would replace all of them.

I would agree with the earlier recommendations from Eric and Dave. Have a qualified person restore this TV, or at least check it out.

You can't restore a TV electronically by simply plugging in a couple of new parts, just as you can't rebuild a worn-out 50-year old engine by putting in new sparkplugs. This is not a good project for someone with no electronics experience. High voltage that can injure you, lots of complexity.

Just my $0.02.

Phil Nelson


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 Post subject: Re: Dumont RA170
PostPosted: May Wed 02, 2012 4:29 am 
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philsoldradios wrote:
I would agree with the earlier recommendations from Eric and Dave. Have a qualified person restore this TV, or at least check it out.


Absolutely. I'm just trying to educate myself before I take it anywhere, so I'll know what they're talking about.

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 Post subject: Re: Dumont RA170
PostPosted: May Wed 02, 2012 5:56 am 
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Learning is good!

Enjoy,

Phil Nelson


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 Post subject: Re: Dumont RA170
PostPosted: May Wed 02, 2012 3:56 pm 
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Snapping was hi voltage arcing, maybe burning the dust bunnies off. Any long term use of that TV will be down hill performance..


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 Post subject: Re: Dumont RA170
PostPosted: May Wed 02, 2012 3:59 pm 
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toyfreaks wrote:
philsoldradios wrote:
I would agree with the earlier recommendations from Eric and Dave. Have a qualified person restore this TV, or at least check it out.


Absolutely. I'm just trying to educate myself before I take it anywhere, so I'll know what they're talking about.

If you want to educate yourself there's a Marcus TV servicing book, 1955 edition on EBay.


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 Post subject: Re: Dumont RA170 ... NOW WHAT?!
PostPosted: Jul Tue 17, 2012 11:14 pm 
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toyfreaks wrote:
I'm just trying to educate myself before I take it anywhere, so I'll know what they're talking about.


I figure before I have somebody test the tubes and look at the power supply, I should at least dust the inside of this honey.

Then I noticed there was some brittle plastic around the ferrite collar on the CRT stem.

All I did was touch it, and it crumbled into pieces all over the main board.

Based on where it came from and the shape of the remaining pieces, it appears to have been one (or more) plastic insulator(s) between the magnet and copper coils that also held the connector wires.

Anybody have a photo or diagram of what this should look like when it's healthy?


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