Rca 730-tv1 - Videokarma.org TV - Video

vts1134 · #1 06-04-2011, 09:11 PM

I started work on my RCA 730-TV1. Originally the radio just hummed loudly so I thought I would do a recap on the radio side to build the confidence that my Majestic 1600 is starting to take away. It didn't turn out that way

. Now it turns out that I have two incomplete projects. The problem was I made a pretty bad mistake when I replaced the filter capacitors. I replaced a 350volt and a 450volt with 160volt caps

. After a slow start up and 3 or so seconds of full power one of the caps gave up. I've replaced the two mistakes with 450volt versions but I'm concerned that I have damaged other components through my inattention to detail. Are there other steps I should take before powering the radio back on? Besides taking my head out of my derrière before doing any more work.

Here is some pics of the set. It really is a stunningly beautiful piece.

The knobs on the front of the radio aren't missing, just removed.

Sandy G · #2 06-04-2011, 10:05 PM

I HOPE you didn't "Woof" yr set, 'cause it is GORGEOUS !!

wa2ise · #3 06-04-2011, 10:55 PM

The only parts at risk would be the power transformer, rectifier and a few resistors in the power supply. If the set now works, you should be fine.

vts1134 · #4 06-05-2011, 06:45 AM

Quote:

Originally Posted by wa2ise

The only parts at risk would be the power transformer, rectifier and a few resistors in the power supply. If the set now works, you should be fine.

But should I be fine to power it back up? My fear is that if I did indeed fry something else then powering the set up will cause more damage.

I still can't believe I did that

Reece · #5 06-05-2011, 06:58 AM

Check ohms of any large resistors in the power supply circuit. Be sure the electrolytics are in there correctly with respect to + and -, and pull the rectifier tube, leave all other tubes in place. Use a dim bulb arrangement, say a 60 watt bulb in series with the power cord. If the bulb stays dim, you're probably OK.

If normal brightness, xfrmr primary may be shorted.

Let's assume dim bulb. Remove dim bulb and plug set into variac, bring up easy to normal voltage. All tubes should light, but of course no sound due to rectifier being out. Feel power transformer. If after 20 minutes

it's still just warm to touch, you're OK. Turn set off, plug rectifier back in, off you go.

Watch/touch/sniff carefully for a while in the power supply area.

old_coot88 · #6 06-05-2011, 10:30 AM

Quote:

Originally Posted by Reece

Watch/touch/sniff carefully for a while in the power supply area.

Old techies gots a 'nose' for servicing.

Electronic M · #7 06-05-2011, 02:51 PM

I once had a Zenith hotchassis radio phono that had recessed chassis bolts and an above chassis cardboard lytic. So I sniped the lytic and soldered replacements in above chassis, I pluged her in and one of the replacement sections expoded! I replaced the section with a higher voltage and it exploded again! Later on I managed to unbolt the chassis and discovered that a lead conected to the cord that ran next to the terminal for that section of the cap had lost it's rubber and was shorting 120VAC to the cap. I replaced the cap again as well as the wire and presto the audio returned, and no more exploding cap.

These sets are pretty durable if you don't leave them on too long after a failure.

Tom C.

vts1134 · #8 06-05-2011, 05:30 PM

Dim bulb came up dim. All checked out so I fired the set up. "BC" (I'm assuming this is AM?) has no audio at all. FM hums loudly. I didn't check Phono because the phonograph in the set is not the original so I don't have it plugged in. I did plug in a computer running Pandora and what did I get??? Something so beautiful that it brought tears to my eyes

. My wife's head peaked up and she had a surprised/curious look on her face. My first sign of life! My first success!

.

vts1134 · #9 06-05-2011, 05:33 PM

I've never uploaded anything to YouTube in my life but this is special.
http://www.youtube.com/watch?v=vBqazEimoIU
Kinda boring stuff to most, but beautiful to me

.

Now to figure that pesky AM/FM.

Reece · #10 06-05-2011, 05:37 PM

So the audio section works! Great. Did you test all the tubes? Sure the tubes are all in their proper sockets? Clean bandswitch (BC=broadcast=AM/FM/phono) with spray cleaner and rotate back and forth. Pull each tube, spray pins with cleaner, immediately plug in and out of socket a few times. Does this set have its AM loop antenna connected?

vts1134 · #11 06-08-2011, 09:08 AM

I was looking over the bottom of the radio chassis and I found a cap who's connection doesn't jive with the schematic. I've looked over the pictures I had before I started recapping and as far as I can tell I have put the new cap in the same place as the old one was. Perhaps some one else serviced the unit and put their cap in the wrong place before me? Perhaps I'm miss reading my pictures and put it in the wrong place myself? Any how the cap is C7 and it is in the picture of the schematic below. It is shown between pin one and pin two. From my extremely extremely limited experience thus far I have always replaced electrolytic capacitors with the negative side to ground. This schematic doesn't show that though. Of course I trust a schematic over my own knowledge but I just wanted to ask here to make sure that it is right.

I also want to confirm that pin numbering on tubes always run clockwise. In the picture below pin one starts at 12 o'clock and goes clockwise from there. Is that correct?

Reece · #12 06-08-2011, 03:24 PM

The + on the C7 electrolytic goes to the cathode (pin 1) as shown. If you check some other ratio detector circuits you'll see this also.

Tube pin numbers always go clockwise looking at the bottom of the tube starting from the space on minis or from the key on octals and loctals or in the case of large pin tubes, from the large pin on the left with the large pins at six o'clock.

teevee · #13 06-08-2011, 07:27 PM

Um, the + side of the cap goes to ground. One of the 6AL5 cathodes (Pin 1) goes thru a 910 Ohm resistor to ground. Likewise, one 6AL5 plate (Pin 2) goes thru a 820 Ohm resistor to the - of the cap. This is a fairly normal ration detector circuit. It's worth checking out C7, because a surprising number of caps used in that application are found to be open. Basically, the FM sounds not quite right. The voltage developed across C7 is also used during the FM alignment...

teevee · #14 06-08-2011, 07:31 PM

If the positive lead of that cap is going to pin 3, (the two grungy brown (?) wires in the pic, your problem is solved.. That is the 6.3V filament connection, move it over one pin, or to any convenient ground.. Can't tell from the pic where the lead is really connected..

Reece · #15 06-09-2011, 01:18 PM

Whoops, you're right teevee about the + going to ground. I was just following that line right across to the left to pin 1 and tripped over everything in my path! Now where are my glasses...

Looks like per the photo and the schematic, pin 4 is a ground point as well as the heater connection. A ground lead also goes to the center shield post of the tube socket.