Hello all,
New to the forum here! I have a Magnavox Astro Sonic console model 1ST689. The unit has been sitting not used for a couple years now. I recently cleaned it up and powered it on and the radio works fine. But, when I turn it to PHONO to play a record, there is no sound coming from the speakers. I can hear the record playing from the needle, but no sound comes out at the speakers. If I switch it back to AM radio, there is radio noise projected from the speakers. Then, if I switch it back to PHONO with the record playing, there will be about 5 seconds of sound from the record coming through the speakers, then it fades out like it is being turned off. I'm honestly not sure where to start, but want to get this thing playing again. Any help and suggestions are greatly appreciated!
Thanks! Mike

It could be a switch problem, or cable connection loose.
If that unit has a pre-amplifier circuit for a magnetic cartridge there might be a problem there.

Did the record player work before ?

Unplug the power cord, and take the rear panel
off of the console for the following:

1. As Tim noted, it could be the function
selector switch is corroded or oxidized on
the "Phono" position.
Spray the switch with electrical cleaner,
and rotate switch positions back/forth.

2. Clean the RCA audio cables' connectors and RCA input
jacks at the record changer.

If the cables into the amp have input jacks,
do the same cleaning.

3. Possibly the phono cart is bad.

With the Phono position selected,
touch each of the tonearm lead wires
at the cartridge,

Two of those wires should give a loud
buzz when touched with finger or screwdriver.

4. Be careful not to touch the amplifier that may
have stored electrical charge which can harm you.

Hotwax

I highly doubt a bad cartridge or selector switch would cause the sound to fade out a few seconds after the switch is changed to the phono input.

Please don't take this the wrong way - but are you sure the amplifier is turned on while testing a record? I ask because it sounds like something is shutting down after the switch position is changed. Remember, these stereos have a power switch in the amp for the radio/aux, but that is not used for the phono input. Instead a switch in the changer provides power so that it can be shut off automatically at the end of a record. Did you try wiggling the changer power switch or cycling it several times? Can you see lights, hear hum from the speakers, or any signs of life from the amp while playing a record?

Thanks for all the insight! Hotwax, the record player did work normally the last time I used it a couple years ago. I got as far as spraying some electrical contact cleaner through the knob stems as much as I could without taking the chassis out of the console. I also pulled the rca wire jacks off from the changer and the chassis and sprayed those as well, to no avail. That's as far as I got for the time being do to my work schedule.

Classicelectronicsguy, I did not realize there was a separate switch in the amp. I only ever had to turn on the main power control, which controls Timbre and turn the selector to PHONO and it would play fine. Would would the amp switch be?

I am going to try the other tests with the tone arm as soon as I can.

Thanks!

Well, I am just speculating here as I haven't seen your Magnavox, but there would be the main power control you mentioned and the switch on the record changer. I am just suggesting you try to determine if the power is still applied when switching over to phono. On many consoles of this era the main power was routed through the switch on the changer (so they would shut everything off after the last record), and that switch was bypassed when listing to radio or tape. If you were able to locate a schematic we could confirm.

Sounds good. I will send over some pictures tomorrow evening. I believe there is a schematic inside the cabinet that may verify that and I can send over as well. I did have a chance to check if there was any output from the tone arm. I can put my finger over the cartridge and it's silent, until I switch it from PHONO to radio and then back to PHONO, which you can hear amplified noise for a bout 5 seconds then it fades to nothing, same as on a record.

The cartridge is fine.

-David

Here are some some pictures of the stereo. Hopefully this helps. I tried taking the schematic out, but it was starting to tear.

Don't try to remove the glued-in schematic diagram! They should be available on-line somewhere.

That last photo shows the record player connections. The red-black-yellow is the power, two wires are the power and neutral to the motor, one wire is the switched power going back to the amplifier keeping it turned on until the last record finishes. My theory is that this switch or connection is not working as it should and the power is not staying on when trying to play a record. Do you have a way to take some voltage measurements?

I do. I have a digital multimeter.

Are there certain values I should be looking at in checking that switch? Would it work to back probe the connector being connected to the motor?

I couldn't see the multi selector switch with the label PHONO at first in the photos, but the label is just under what's marked STEREO. Anyways, if it were me, the first thing that I would do is to try spraying that multi selector switch down with some good contact cleaner. Personally, I prefer the Radio Shack Cleaner and Lubricant (Cat. No. 6400148).

Actually, I experienced a similar problem with my 1963 Zenith MT-1959H AM/FM/PHONO stereophonic wood floor console about three years ago. What I found was that one of the electrical contactors for the PHONO selection was too far gone for any contact cleaner to do any good. Fortunately, after reviewing the schematic, all that was needed was to simply solder a bridge across that contactor.

I suspect that is the same problem here. It is not a good design to run power through a selector switch intended for low-level audio signals. And that selector switch has to carry the entire power load of the console. I bet the contacts are toast.

-David

Can't be the selector switch. Could be the wiring to the switch on the record changer.

What's the best way to get to that switch? Pull the tuner chassis out?

Yes, that's the only way.

-David