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 Post subject: Rca pushbuttons won't work
PostPosted: Sep Wed 29, 2021 11:11 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
In the past I had recapped three of these radios with out a problem.
I have recapped this radio and aligned it a couple of times to make sure it is playing good.
The AM band plays good
I can't get the push buttons to work. All I get is a very small hum in the speaker.
I cleaned the band switch several times; checked the continuity of the wires going to the push buttons.
I have tried another set of bush buttons from the same model radio.

I did replace C59, C 69, and C 61. R 29 is good
Any ideas are sure welcome
Here is the schematic

http://pacifictv.ca/schematics/rcaa33data.pdf

Dan in Calgary


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Sep Thu 30, 2021 4:07 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 8309
Location: Near Brandon, Iowa
The pushbutton presets only work on the standard broadcast band. Since that band works OK in manual-tuning mode, you can conclude that all of the active gain stages are working.

However, the tuning presets use different oscillator and antenna-tuning circuits than the manual mode. If just one of the pushbuttons was dead, you could reasonably suspect that the tuning pair for that preset (oscillator coil + compression cap) was defective. All of the pushbuttons being dead point to a more likely cause being the manual/automatic switch being dirty or damaged.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Sep Thu 30, 2021 5:23 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
Thank you for the reply;
I will recheck the switch that changes from manual to push buttons ,
although I have cleaned all the switches several times.
Dan in Calgary


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Sep Thu 30, 2021 5:32 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 8309
Location: Near Brandon, Iowa
chaz wrote:
Thank you for the reply;
I will recheck the switch that changes from manual to push buttons ,
although I have cleaned all the switches several times.
Dan in Calgary

Cleaning may not fix the problem if there is a mechanical issue. Examine the switch contacts for bent, burned, or broken parts.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Sep Thu 30, 2021 8:01 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
I have examined the switches many times, BUT I could have missed something.
I will do it again [more closely]
Dan in Calgary


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Sep Thu 30, 2021 8:53 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6404
Location: Minneapolis, MN USA
Push button switches often have individual wires for each push button plus a single connection in common to each switch. So a five bank switch may have six wires. Ensure that common connection is working. If the common connection is defective none of the push buttons will work same as if the manual/auto switch is not working.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Mon 11, 2021 2:11 am 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
I am sorry I didn't get back you you guys earlier. [under the weather]
I have another RCA model A33, so I recapped it and the push buttons
work on it. I took the push buttons that work and tried them on the radio that the push buttons don't work.
I still have the same problem, but now I know that the fault is not with the buttons.
I also inspected the rotary switch that the wires from the push buttons go to , and do not see any bent pieces
or anything unusual.
Is there some component that I should check?
I already changed C 59,,C69 and C 61
Thanks
Dan in Calgary


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Mon 11, 2021 2:12 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6404
Location: Minneapolis, MN USA
This needs to be troubleshot by checking for function of stages, not looking for a magic bullet component replacement.
The band switch is complex with 7 dual gang sections.
You can have lost of reception due to failure of the oscillator else failure of the front end tuning circuits.

Do any of the short wave bands work ?
Do you have a frequency counter (or scope) ?
Do you have a signal generator ?
Can you trace wiring against the schematic ?

If you have a frequency counter you can check for presence/absence of an oscillator signal with a sniffer coil.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Mon 11, 2021 6:38 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
Thanks Dale;
None of the short wave bands work. On the short wave I just get a very low speaker hum [normal].
I have a signal generator, but no frequency counter or scope.
I can trace most wiring on a schematic, BUT I find it difficult to follow the schematic when it comes to the band switches.
Sorry but I don't have all the technical skills as I am self taught ;using the forum and ''The Elements of Radio''.
Dan in Calgary


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Mon 11, 2021 7:44 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6404
Location: Minneapolis, MN USA
Dan,
This is a very complex set set and I am glad you did not take offense to my terse and direct questioning.
If broadcast manual tuning works, but broadcast push button and all shortwave bands doesn't work, this points to the band switch. I agree that band switch diagrams in general can be difficult to trace because they are often drawn without enough clarity to fully discern what is happening at each position.

Do you have another working set with shortwave bands that you can listen for the oscillator from the set under repair ?

I'm trying to narrow down which wafers in the band switch are not working.

Also hoping the forum has some suggestions as you have already requested.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Tue 12, 2021 6:16 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
Dale;
Sorry but you have ventured into an area that I am not familiar with.'' LISTEN FOR THE OSCILLATOR''?
I wish I had more insight into the various areas of radio repair. If you could give me some clarification
on how I would do this it probably will be helpful.
Thank you
Dan in Calgary


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Tue 12, 2021 11:40 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6404
Location: Minneapolis, MN USA
The oscillator is the heart of a superheterodyne receiver. It can be thought of as a signal generator. For your radio, on the broadcast band, it generates a signal 455kc above the position shown on the tuning dial. For example, with the suspect radio, in manual mode for the broadcast band, tune it to 800kc on the dial. Now tune a known good radio to 1255kc on the dial. As you tune above and below 1255kc, the sound from the good radio should change from white noise/hum/static to a rushing or noticeably silent sound that comes and goes as you move the dial pointer. If you put the suspect radio in push button mode, you can check for the oscillator in the same way except you need to know which frequency/station those buttons are currently set. You can try all of the push buttons while tuning the good radio instead to see if you can find the oscillator signal in the suspect radio. For the shortwave bands, you would do something similar to the manual mode in broadcast band but you would need a shortwave radio to look for the oscillator signal from the suspect radio since that oscillator will be at a shortwave frequency depending upon which shortwave band you are on.

Some folks confirm if oscillator signal is working by checking grid voltage on the oscillator or converter tube. I prefer to use a frequency counter and a sniffer coil.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Wed 13, 2021 8:21 am 
Member

Joined: Apr Sun 08, 2007 6:47 am
Posts: 5208
Location: British Columbia
These are very similar to the ones used in the RCA A-22/25 I think, in those sets the band switch has to be set at P.B for the buttons to work. There are also three wires that come up from the chassis and connect to sockets at one end of the P.B bank, the other end on the bank has a phono jack with a cable that plugs into a three pin socket on the chassis. If you get the three wires mixed up, which is easy to do, the pushbuttons will not work.
Regards
Arran


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Wed 13, 2021 3:19 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
Thanks Arran
I have done radios with that particular set up. On this one it is a little different
and the RCA jack is on the back of the chassis.

On this radio there are not three wires coming up to the push buttons. I have the push buttons working on another RCA model A33
, so I know that the push buttons work. Thank you for your input.
I hope to get to this radio today and try to do what Dale suggested.
Dan in Calgary.


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 Post subject: Re: Rca pushbuttons won't work
PostPosted: Oct Thu 14, 2021 10:57 pm 
Member

Joined: Nov Mon 05, 2007 11:08 pm
Posts: 3179
Location: Calgary Alberta
I use the same [good] push buttons for this experiment The push button was set at 660, so I set the
other radio as close to 1115 as I could
I tried the method of using another radio and listening for the changes as I tuned across the dial.
It seemed to work on the A 33 that the push buttons work on
When I tried the same thing on the radio that the push buttons won't work on I could get the signal on
Am but not using the push buttons, and they were still set to 660
I am not sure what that tells us ,but that is the result.
I hope I am learning something here.

I appreciate the help, and i only wish I knew more about this.
Dan in Calgary


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