Magnavox Radio and Hum Problem

[magnag]

I have a 1965 Magnavox Micromatic Astro-Sonic and I have cleaned the record player and no problem. After that I had no sound so I replaced about 21 capacitors and it sounded great for about an hour then went silent. I get a hum and buzz and I just don't know what to do anymore. Panel lights on. I can hear a portable CD player with RCA inputs in AUX. I sprayed the pots with LPS Electro Cleaner. I have the Sam's 841-6 schematic and I've tried hard to follow. I've had this console since the 1960's and I think it's worth fixing.
I've done a lot of research on Google and Youtube to learn and find answers.
I'll answer any questions asked to my ability.

Thanks,

magnag

 

[NAD80]

Hello magnag. Welcome to AK. Found this web site. http://vintagehifi.net/index.php?topic=186.0 Looks to be a good one on the Magnavox consoles. Don't have a console but around here there are plenty of people who know things on the consoles. Hopefully someone will chime in on that one. I have heard of that one here. Did the switches get cleaned also? Also go to the solid state forum. In the search box type "Magnavox Astro Sonic" and you will get quite a few previous threads on the consoles. Good luck with the console.

 

[magnag]

Hello magnag. Welcome to AK. Found this web site. http://vintagehifi.net/index.php?topic=186.0 Looks to be a good one on the Magnavox consoles. Don't have a console but around here there are plenty of people who know things on the consoles. Hopefully someone will chime in on that one. I have heard of that one here. Did the switches get cleaned also?

Hello NAD80,
Thanks for the link. I've also been to that site and one other to ask what to do. I've cleaned the pots and the function switch. I used a brass cleaner followed with a contact cleaner on the function switch and it looks clean and I hope I did right but I get a lot of static when changing modes. I'm just not getting any AM/FM. I know that the phono sounded good until all of a sudden the sound quit.

magnag

 

[NAD80]

Contact cleaner is ok for the switches. Check out the DeOxit thread on the use of the stuff in the beginning on this forum. Check out CAIG website to see the different types of cleaners and lubricants as a reference. Don't think the brass cleaner should be used on the switches.

 

[magnag]

Contact cleaner is ok for the switches. Check out the DeOxit thread on the use of the stuff in the beginning on this forum. Check out CAIG website to see the different types of cleaners and lubricants as a reference. Don't think the brass cleaner should be used on the switches.

I used Tarn-X with a Q-tip and cleaned it up with rubbing Alcohol and only on the function switch where I could see the contacts and not into the pots.

magnag

 

[NAD80]

OK. Hope you can get it working. My dad had a sears console. He played his opera so that everyone outside could hear it.

 

[magnag]

OK. Hope you can get it working. My dad had a sears console. He played his opera so that everyone outside could hear it.

I've got stacks of 78RPM's and one is one sided Caruso. I want to get this thing running so I can download to my computer and make mp3s. Not many record players with 78.

magnag

 

[nj pheonix]

Not saying this is the answer (I hope it's this simple). Many years ago I used tarnx to clean sled contacts on a tt. It worked great for a short while. Then had problems. If its not cleaned off completely it becomes at least resistive if not outright corrosive. So it "might" be just that.
A few other thoughts based solely on your description.
Cold solder joints.
An electrolytic that possibly went in backwards and crapped out
A resistor that was under value (read wattage) that failed.
It is also possible one of your tubes crapped out.
Certainly not a comprehensive troubleshooting guide but points you at some low hanging fruit in the chain

 

[magnag]

nj pheonix,

I woke up this morning with the same line of thinking about buying Deoxit regardless of the cost. The symptoms point to the function switch and if worst comes to worst I'll replace it. I need new soldering iron tips anyway so I'll get them too. The solder joints near the speaker wires haven't been done yet. I've checked a couple of resistors by unhooking one end to test the value and they were OK. No tubes.

Certainly not a comprehensive troubleshooting guide but points you at some low hanging fruit in the chain

Just what I need to help get me started.

Thanks for the input,

magnag

 

[magnag]

I bought Deoxit Fader F5 and sprayed the pots and function switch and that greatly reduced the static. I'm still getting hum. I can hear music from the CD player using the RCA inputs of TAPE with hum. However, I am not getting AM/FM radio. A new soldering tip was used to re-solder some of the old points.

magnag

 

[KentTeffeteller]

Also, Astro-Sonic= Solid State i.e. transistorized.

 

[magnag]

I could try to check the transistors. It's a painstaking job but somebody has to do it. I took out one and discovered it had four legs and it checked OK. They are hard to find and expensive. I'm checking them in circuit and getting numbers but not spec numbers. I would need to take them out of circuit to get an accurate reading. They include AM and FM amps, etc.

magnag

 

[magnag]

I took out the Base leg of Q17 (transistor, Sam's 841-6) and measured it. I set the DMM at Diode and at 20KΩ and got different results. I pasted them here and I need to know if I have a good transistor?
I'll check all the transistors that I can get to as long as I know what I'm doing.

Q17 PNP
DMM @ Diode
B-E 3.04, 0.21
B-C 3.04, 0.21
C-E 2.84, 2.64

DMM @ 20KΩ
B-E OL, 5.94
B-C OL, 5.45
C-E OL, 4.04

I'm finding things. Q14 and Q19 (Drivers) have drops between Collector and Emitter each way.
Q6 (AM IF-1st FM IF AMP) is 0.00 between Base and Collector each way.
A couple of others might have drops between C & E one way.

magnag

 

[magnag]

I'm almost done! I cleaned the function switch again with rubbing alcohol. The hum is mostly gone when I put my hand over the red/white wire that goes to the long board near C78 and R79. I put in a new Q6 transistor and a dozen resistors on the long board and near the output transistors. I am now getting both AM and FM. I tweaked A5, A6, A&, A18, A19, A21, and A22 to get the more stations and to align with the dial. I need to double check Q11 in order to get the light on when in stereo. Soon I'll put the chassis back into the console. I'll add RCA's for the Tape Input and Tape Output and maybe a short extension cord to the ACV output to supply a mp3 player. I've really learned a lot about radios and electronic components.

magnag