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 Post subject: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Mon 19, 2011 2:52 am 
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Joined: Mar Wed 30, 2011 5:37 am
Posts: 931
Location: GA
I've been working with this for about a month or so on and off. I got so disgusted with it that I set it aside when my Motorola VT 73 came along, but with the VT-73 almost ready for reinstallation in the cabinet, it't time to get back to this. Besides it's on my dining room table, and I have co coming for Christmas dinner, so I've got to get it cleaned off. Sams 375-4

The seller on Ebay empahsized the deep red color of the metal cabinet which is what attracted me to it. The listing said it didn't power up. After taking the back off, I tried it. I was planning on recapping it anyway. The tubes it and that's all. I noticed the B+ fusible resistor was deteriorated and checked open, so I tacked a new wriewond in place. It immediatedly burnt up in an orange glow. I then pulled the chasis and replaced the electrolytics and changed the old rectifiers to new diodes. Putting in a new resistor had the same effect. I then began replacing the paper & bumble bee caps and burnt up about 3 more wriewounds before I noticed that L23 (1.6ohm) choke on damper tube pin 5 arched. It was a good connection, but I moved the coil slightly, and that go the B+ fixed. However, the coil eventually burnt out, and I replaced it.

Here is what I have now with all paper caps and electrolytics replaced: Almost little vertical. In the pic I provided, the height and lin controls are set at max. Sound comes and goes, no video signal reaches the screen, just horizontal lines.

On checking voltages, I have 3 areas of descrepancies:
V11 10DE7 Vert Mult & output tube. Pin 6 SB 120V. I have 24V. Have replaced paper caps and resistors in the circut. V10 feeds this tube. Plate of V10 (3CS6) is correct, 40V.

V12 6CG7 Horiz Mult Pin 6 (plate) SB 150 V, abnd I have 131. All other votages on tube are fine

V6 12BY7 Video output All is correct on tube but pin 7. It Sb 105V. One time I can measure it and get 245V, and meaure it again and get only 43V. That puzzles me.
Any idea on what to check next?
Thanks a bunch
Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Mon 19, 2011 4:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 747
Location: Littleton, CO USA
That set was actually made by Sylvania.

Check the vertical controls and look for dirt on the PC board. Board breaks are also common. The .027 in series with the yoke and the .022 in series with the width coil are also suspect. They will load the boost.

Are you sure the horizontal is on frequency? If not, short out the horiz freq coil. It should get close. Then remove the short and adjust the coil for picture sync.

If You have no video, there is probably too much AGC voltage. Check the voltages around the 5BR8 after first trying to adjust the AGC. It is very touchy. Do not overlook the 1N295 video detector if there is still no video. An ohm meter check is OK. There could be trouble in more than one circuit so deal with one symptom at a time. Leave the vertical until last.

The video amp plate will vary somewhat with signal.

Don


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Mon 19, 2011 5:37 am 
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Joined: Mar Wed 30, 2011 5:37 am
Posts: 931
Location: GA
AFter posting tonight, I got back into it and actually made more progress tonight than all other attempts. Coming off pin 1 (plate) on 10ED7, vert mult/output, there is a .1 cap which I replaced. I know I took the old cap out when I put the new one in. But tonight I shined a birght lite in the chasis and saw the cap in the pic exactly in parallel with where the .1 goes. At 1st I though it was an old wirewound resistor. I rechecked the schematic and found it was not supposed to be there, so I cut it out, and have full vertical. Voltages on 10ED7 are about where they SB.

I still have no pic , just snow with some audio. When the audio goes off, wiggling certain tubes on the pc board fixes that. I have checked the PC board, and it is making good ground, but I have not seen any breaks yet. I'll keep looking. The voltage on the 12BY7 on pin 7 is still 43 volts instead of 105.

Don, I'll check your suggestions tomorrow and post the results.
Thanks
Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Mon 19, 2011 5:13 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25790
Location: Detroit, MI USA
I used to know the story behind why RCA was selling those rebranded Sylvania portable TV's that year. It was mentioned in some RCA literature, either a service manual supplement or a monthly newsletter from a distributor to the authorized RCA servicers. Might have been due to a fire at an RCA factory that built portable TV's and took a few months to get back into production.

I had the identical set built by Sylvania with a private brand name on it from a department store. While performance was acceptable when it worked, it was a very poorly built set and one of the worst designs I have ever seen as far as physical layout. For some reason the engineers thought it was OK to mount the one PC board with most of the circuitry directly above the horizontal output and damper tubes, the hottest running parts in the set. The biggest problem when these sets were just a few years old was intermittent solder connections and traces on the PC board, followed by short capacitor life, both caused from all the heat directly below the board.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Tue 20, 2011 1:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 747
Location: Littleton, CO USA
Good work on the vertical.

Tweaking the horiz freq coil should restore the picture.

I agree with Mr D on the poor design. It has keyed AGC, noise inverter, gated sync and three IFs often found in top line consoles, then curiously deletes the horizontal hold control to save cost. Off-On Brightness foils the trained customer looking for a volume control. The heat-sensitive horiz sync dual diode is directly above the HO section as well. PC board mounted customer controls don't help either. The one with the switch is bolted while the others are just flow soldered in place.

I don't know the story behind RCA's rationale for that product. I do know some dealers would not sell it and they didn't run out of real RCA built portables.

Don


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Tue 20, 2011 6:07 am 
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Joined: Mar Wed 30, 2011 5:37 am
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Location: GA
Well I have some good results tonight. Don, I have tried tweaking that horiz control several times to no avail, but thought I'd try it one more time. I was able to get a snowy pic. As far as the AGC, the voltages are too high. It comes from the 220V line and goes to pin 1 of 5BR8 which SB 120V. I'm getting about 216V on pin 1. The 5BR8 sometimes has a purple glow. It checks ok on my checker, but I ordered a new 1 last night as well as a new audio 5AQ5. When the sound goes off, that's one of the tubes I can wiggle to make it come back on. That tube checked questionable. I do believe there is a bad connection on that PC board. Sometimes I can turn it on and get nothing but a raster. Wiggling some tubes or tapping on an IF can or even changing channels will sometimes bring back the sound. Sometimes the sound is there with just lines and sometimes with snow, but tonight with a snowy pic.

I can honestly agree with everything you guys have written me about this set. I thought it was a real pretty set when I saw it on ebay and thought I was getting something. The seller had it for $49, but no one bid. He then dropped it to $29. I was the only bidder at $29. I now know why no one wanted it. When I get it going, it will not be a set that get's much use to this flawed design.


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Tue 20, 2011 8:28 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 747
Location: Littleton, CO USA
This was a typical symptom for that set. Looks more like interference than horiz freq now. Does the fine tuner affect it at all?

The video IFs in that set have a tendency to oscillate. Make sure all the grounds are properly soldered including the shield on the tuner to IF coupling lead, cans, PC board to frame and tube socket contacts.

Check the 3 IF and the 5U8 mixer tubes for shorts/leakage.

Check the IF AGC with a scope or bypass it with a .1 to make sure it’s clean DC.

Avoid tweaking the IFs without the proper set up. They will be OK if they have not been tampered with. You will never get it right by eye.

Ohm meter check on the video detector diode is in order.

Don't be discouraged. There is much to be learned from this one.


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Wed 21, 2011 6:06 am 
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Joined: Mar Wed 30, 2011 5:37 am
Posts: 931
Location: GA
I made a little more progress today. I think I found the bad connection in the PC board, and it was my fault. I had replaced a cap and had a loose solder connection. After fixing that, tapping on IF cans has no effect. The weak, snowy pic and sound stay. I also replaced 3 resistors in the video IF scetion. All 3 were 470 ohm and had drifted up to around 570. Checking the 3BZ6 tubes (3 of them) all checked fine. As far is the tuner tube: The Sams list a 5U8 for oscialtor. The tube layout paper on the back of my HV cage list both a 5U8 and a 5AT8 for the oscialtor saying replace with orig type only. My set has a 5AT8. It checks good. I don't have another 5AT8, but I do have a spare 5U8 which I put in and could get NO signal at all. Are these 2 tubes interchangeable? I may have to get another 5AT8. Tweaking the fine tuning clears the pic up barely, but it is still very snowy & weak (see pic).
Don, you mentioned about the brightness being the on/off switch. When I stared working on the set, the brightness worked. Now it doesn't. Sometime I can try turning it down, and it will dim for about a second then return to full brightness. The control checks good with my meter (1 meg). 220 volts go thru a 470K restistor which I replaced then into the control. Nothing comes out. I recheck it and see if it possibly has a bad connection on the PC board.
I guess I'm gonna have to check that 1N295 diode. It's housed in a can which is soldered to the PC board. That's gonna be fun trying to get that can loose.
Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Wed 21, 2011 6:17 am 
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Joined: Oct Fri 02, 2009 7:05 pm
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Location: Wolfeboro, NH
When you have no control over brightness on a black & white TV, suspect a heater to cathode short in the CRT. If the CRT is shorted, a brightener STYLE isolation transformer intended for a series wired set will restore the set to normal operation.
IN AN UNRELATED MATTER:
Putting the on-off switch on the brightness control would kill the bright spot that would otherwise be left on the CRT each time the set was turned off, thereby eliminating any chance of a phosphor burn.
Pretty clever.
I well remember what a problematic son of a gun these sets were.


Last edited by Mal Fuller on Dec Wed 21, 2011 6:30 am, edited 2 times in total.

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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Wed 21, 2011 6:27 am 
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What are you using for a signal source and how are you connecting it to the set? Most sources these days have a 75 ohm coax output and if your TV is old enough it will have a 300 ohm balanced input on two screws. I don't know if you already know this, but if your set has the 300 ohm input, you need a 75 ohm to 300 ohm matching transformer to get full signal strength into the set.

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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Wed 21, 2011 6:32 am 
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Joined: Mar Wed 30, 2011 5:37 am
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Location: GA
I may have just discovered the video problem. I checked the other tuner tube, 4BS8. My old PACO T-60 checker has 2 tests for that tube. It checks ok on one test but bad on the other. I just ordered a both tuner tubes. I'm gonna put my B&K CRT checker on the CRT tomorrow and see if it does have a short.

Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Wed 21, 2011 11:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 747
Location: Littleton, CO USA
Check the voltage on the brightness control center arm. It should vary from 0 to about 125 as you rotate the control. If it does not, check for B+ on one end and ground (0 volts) on the other. Board breaks are common, particularly on and around controls.

If the voltage varies properly, repeat the test while measuring the CRT cathode. (pin2) If does not vary at that point, remove the CRT socket and test again while measuring pin 2 at the socket. The filaments will go out, but it does not matter for these tests.

Now you are down to three possibilities; open 270 K isolation resistor, shorted/leaky .2 video coupling or CRT. If it is the CRT, replace socket and LIGHTLY tap CRT neck while set for normal picture while watching for flicker from bright to dim picture.

NOS CRTs are available, do not despair.


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 22, 2011 2:33 am 
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Isn't that a series string set? If so, don't unplug pix. tube. Your B+ will skyrocket!
Bill Cahill

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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 22, 2011 4:25 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Littleton, CO USA
It is series string. Let the B+ "skyrocket" long enough to make the tests I suggested. The TV was designed to withstand it in event a tube failed in normal use.


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 22, 2011 5:50 am 
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Don, There is B+ on one end and ground on the other. 0 volts in on the center no matter where I rotate the control. I disconnected the 27K ohm resistor from the center pin, and still could not get any voltage on the center pin. I have already replaced the 270K on center, 470K coming from B+, and .22 cap coming off the 470K.
I did put the CRT on my B&K CRT checker today. On the shorts test, G2 took about 30 or so seconds to finally half light where as G1 half lighted almost instantly. Also I did notice a purple glow in the tube neck which is not there when the set is in operation. I have the set on now, and there is no purple glow.
I'm thinking about trying another 1 meg control for the brightness before I make any decisions on that CRT.
Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 22, 2011 6:11 am 
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Don, One more update. I just did some more voltage checks. 220v B+ feeds the 470K resistor going to the end lug of the brightness. Coming out of the 470K is 106V. When I vary the control, the end lug goes from 106V down to 0 from one extreme to the other. Middle lug stays at 0 constantly.
Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 22, 2011 7:30 pm 
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Sounds like there is a dead short from the center lug of the brightness control to B- or chassis ground. Could be a problem like tin whiskers inside the control, or a short on the PC board near the control.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 22, 2011 8:02 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 747
Location: Littleton, CO USA
With the CRT socket off and no power, make some ohm meter from the brightness center arm to ground on RX1 or RX10 scale. Rotate the control to be sure you are not at the ground end of the range. As Dennis suggests, tin whiskers or an unintended solder bridge are possibilities.

The control is bolted to the PC board. I am not sure the outer case grounded since one side of the AC is anchored to chassis ground and the switch is on the hot side. Don


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Fri 23, 2011 5:57 am 
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Joined: Mar Wed 30, 2011 5:37 am
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Ok, I followed Dennis' and Don's suggestions and have come to the conclusion that the control is bad. I suspected the control all along. I disconnected the CRT socket, sprayed some contact cleaner in the control, set an anaolg meter on R10. It read 0 thru varying the control except at one spot where the needle jumped then went back to 0. The lug that had the 470K coming off the B+ is not connected to the board. It is just connected to the resistor. I made sure it was not shorting out to ground by bending it. I sprayed some more cleaner in the control, hooked up the CRT socket, and powered it up. I got the brightness to work 1 time. Wiggling the control makes the brightness come and go. I've ordered a new brightness control/switch.
I think the poor reception is due to a bad tuner tube. I've got new ones on order. If they don't help, then I'll take the can off and check the Video diode.

Doug


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 Post subject: Re: RCA 17S-7093 Deep Red/Maj Headache
PostPosted: Dec Thu 29, 2011 5:04 pm 
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Joined: Mar Wed 30, 2011 5:37 am
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Location: GA
My parts came today: new brightness control & tuner tubes. I was able to fix the old brightness control temporarily, so I know the control was bad. I'll put the new copntrol in this weekend. Right now, the singal has me stumped. The problem in in the 4BS8 tuner tube. The old tube did not check good in my checker. I got a snowy pic as seen with good audio. The new 4BS8, which checks good, looks like it's overloading. Putting it in just gives a raster. Tweaking the fine tuning will prudice buzzing audio and an overloaded screen. Varying the AC G has no effect except at the extreme where the signal cuts out. Could this be the Video Det diode needing replacing?
Doug


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