Roadside p/u Motorola SK80CW (Help needed)

[SSGNDoc]

My daughter saw this 1960s vintage Motorola SK80CW on a roadside with a “Free” sign on it. She had said a few months back that she would like to get one of those “Antique turntables that comes built in a cabinet someday.” Well she found one. The cabinet is in decent condition except for a broken foot (but the broken piece is there and 8 think I can fix that part to a serviceable state. But when it comes to working on electronics. I’m at a loss. I was never much of an electronics tinkerer. I only know the very basics of how radios and turntables work. The good news is that it does at least seem to hav3 some functioning power and amplification.

The cabinet is in decent shape. The large central speaker cone is torn and is disconnected. Applying some power to the whole unit does get the AM and FM tuners to come on when selelected, but the string for the pulleys and the tuner knob are not routed and are hanging inside the cabinet. Turning the AM tuning wheel manually does see, to indicate it will tune. I live in a somewhat remote area and am not certain of antenna requirements or condition of the onboard ribbon style antenna in the cabinet.

I was not able to do any tuning with the FM side of things.

I know nothing of the technical requirements and working of this type of unit other than what I have described. The turn table does not seem to drive. Ik’m not even certain of the motor placement or arrangement, but I do see one pulley with no kind of drive belt, when I look underneath. The remaining 4 smaller speakers do at least crackle when power is applied and when the needle is contacted lightly.

So…we have some power working.

My daughter’s priority would be to get the large speaker repaired or replaced and get the turn table working properly. I’d like to get the radio side of things working along with all of the lights. Some of the knobs illuminate. Some don’t. The light in the turntable side is not working. The right rear corner cab8net foot is broken, but the piece was inside the cabinet with the tuners and I think I can drill, dowel and glue repair that.

I’m fairly mechanically capable but don’5 know where to start for diagrams, repair manuals, instructions or even how some of the basic parts should be laid out, such as the turntable drive motor, pulley and belt orientation/routing. Tuner knob string routing and calibration with the actual tuners and frequency indicators, etc.


Any help on where I should start, resources and guides on these repairs, How not to do damage as I try to fix items, Where to obtain replacement parts of this vintage, etc. would be deeply appreciated.

[SSGNDoc]

Some more pictures

[electra225]

I hate to be the dog in the manger here, but please complete your registration requirements. We have had to implement enhanced security lately to fight off the spambots who like to post nonsense. We require all new members to post their location in their user profile and to post an avatar by their third post, which I just approved for you. I have "stretched" the rules a tad to accomodate you, but we appreciate you posting pictures while joining our forum. Being difficult at times is my job as administrator. Thank you for your cooperation and understanding...

As to your stereo, what's not to love? Drexel cabinet, Vibrasonic, tubes. As to your busted speaker, it can be repaired successfully by using speaker glue and paper towel to repair the rip in the cone. We have lots of technical expertise on this forum that can help you work thru the electronics. If you have the desire to learn, a soldering iron, and a meter, we can talk you thru the repairs. IT is not difficult in most cases and is rewarding and fun hearing it come back to life. Good luck with your project.....

[danrclem]

How about a picture of the cabinet? From what I see it looks like it's a really nice unit and, with it pulling 240 watts it must have a healthy amp.

[danrclem]

I looked it up and it looks like you probably hit the jackpot. Nice cabinet style and what looks like a great amp.

https://www.radiomuseum.org/r/motorola_ ... 9hs96.html

[TC Chris]

The most common problem causing "no sound on [FM, phono, etc.]" on unused equipment is a dirty switch. Sometimes just working the selector switches can give some response. It may be intermittent but at least you have ID'd the problem. The the basic issue is the power supply--120Volts AC to high voltage DC and low voltage AC for the tubes. The filter capacitors are components that die of old age often, and then they go belly-up, they can take expensive parts with them. I'll let the Motorola guys point out which ones they are. They are a cheap update but do require soldering and getting polarity right.

Chris Campbell

[electra225]

I think Bill has a Motorola stereo that uses the 3DG4 rectifier. That tube is commonly used as a TV tube. That amplifier should be a good performer.

[SSGNDoc]

How about a picture of the cabinet? From what I see it looks like it's a really nice unit and, with it pulling 240 watts it must have a healthy amp.

The cabinet has a few minor dings. The whole thing is pretty dusty. My bet is that it probably sat in a garage for a while or just in a corner collecting dust for a while before being brought to the curb. The whole unit is pretty heavy, with a cherry wood cabinet.

[SSGNDoc]

The most common problem causing "no sound on [FM, phono, etc.]" on unused equipment is a dirty switch. Sometimes just working the selector switches can give some response. It may be intermittent but at least you have ID'd the problem. The the basic issue is the power supply--120Volts AC to high voltage DC and low voltage AC for the tubes. The filter capacitors are components that die of old age often, and then they go belly-up, they can take expensive parts with them. I'll let the Motorola guys point out which ones they are. They are a cheap update but do require soldering and getting polarity right.

Chris Campbell

Right now it would be hard to tell with no way to really tune it, and with no idea of the condition of the antennas. The AM and FM units at least seem to “come on”. Then my location isn’t super conducive to getting much in the way of AM very well even with my modern car stereo.

I know I want to replace the power cord. And obtain a schematic to give me some idea of how many capacitors I may be looking at. As stated, I’m pretty much going in blind on this type of electronics. I’m already doing some research to try to be able to identify capacitor types, so I can pick out the ones that need to be replaced and then understand what I need to get in the way of replacements to restore function and increase the reliability and durability of the unit as I go.

[SSGNDoc]

Right now I’m trying to formulate a logical order to go through the unit systematically to ensure I address things in a manner to prevent damage while trying to identify what is good and what has gone bad.

In doing some research it seems the record changer is likely made by Voice of Music. I’ll need to figure out what model it is to try to get some parts for it as well, I’m sure.

[electra225]

You should start in the power supply. Without a stable power supply, nothing else is going to work. Plus, there are parts in the power supply that, should they fail, severe or terminal damage may occur. Parts that fail and can cause damage are the filter capacitors. Once you have obtained a schematic for the amp and tuner, these parts can be identified on the schematic, then found on the chassis. Parts for the VM (Voice of Music) changer are readily available from Gary at VM Audio Enthusiasts in Michigan. VM changers are generally easy to service. Dried grease that has turned to glue is the leading cause of changer malfunctions. Drive tires and motor mounts may also need replacement in order for the changer to work right. Take it a section at a time, moving thru the chassis and components in logical order. Troubleshooting is preferable to "firing the parts cannon", just throwing parts at it. Get the schematic, then we can walk you thru the various areas. It not terribly difficult. Take pictures, make notes, don't be afraid to ask questions if you get stuck. That is what we are here for. Following someone else's project is as much fun as doing one yourself. Good luck.

[SSGNDoc]

Best place to find schematics?

I had kind of arrived at the same logical conclusion, that I should probably follow the pathway of the current. First though a good cleaning of the interior of the cabinet is needed as well. So, that seemed like a fairly simple place to start before really “digging into anything” in any real depth.

So…getting started by gently removing the heavy dust with a soft brush and vacuum. Then removed the main power chassis to clean it a bit better with some Q-tips a soft toothbrush and some alcohol. It has some rust spots but I’m not getting aggressive with any cleaning at this stage. Just wanting to be able to have a clearer picture of exactly what I have starting out. I did gently pull tubes, one at a time, and give them a wipe down with a lint free cloth and some alcohol, then replaced each tube before removing the next. I then took a look underneath to get a picture of that wiring and the capacitors just to have an initial look.

(I have to admit the underside is more intimidating to me than the top, as a complete newbie to this type of stuff.). I took pictures of wire routing and orientation before I removed the chassis and also masking tape labeled some of the wires so I would know how the go back on once I put the chassis back in.

Here is the limited bit of cleaning and inspection prep that I did today.

[SSGNDoc]

The basic tube layout schematic and a closer view of the rectifier tube and the large capacitor.

[TC Chris]

Looks like most of the under-hood capacitors are disc ceramics, which are very durable and will not demand replacement like the more usual wax-and-paper varieties do. Bear in mind that audiophiles take the view that ceramics sound worse than tubular film caps, but you can wait decide if it sounds too "brittle" for your tastes. At least they won't fail and endanger other components.

The big can capacitor is the one more likely to fail. Some say test first and replace only when needed. After years of just plugging things in and seeing if sound came out (or smoke), I now favor the school that says "replace it." Since modern electrolytic caps are physically much smaller, there's room to mount them under the chassis or "restuff" the old can.

Chris Campbell

[electra225]

There might be a member of the forum who has the schematic you need and would share. Failing that, "The Schematic Man" is a good place, but is not free. He has downloads or you can get the original paper manuals. I personally prefer the original paper manuals, lest there be missing information. You can take it to a office supply store and have a blown-up copy made if you would like. If you have a copy made, you won't wreck the original making notes on it, but you can make notes on the copy without worrying about it. If you put the chassis on a hunk of clean cardboard to work on it, you can use the cardboard for notes without wondering where you put your notebook....

PB Blaster works well to get the gunge off the chassis. You want to be careful wiping the tubes lest you remove the markings.

[SSGNDoc]

Looks like most of the under-hood capacitors are disc ceramics, which are very durable and will not demand replacement like the more usual wax-and-paper varieties do. Bear in mind that audiophiles take the view that ceramics sound worse than tubular film caps, but you can wait decide if it sounds too "brittle" for your tastes. At least they won't fail and endanger other components.

The big can capacitor is the one more likely to fail. Some say test first and replace only when needed. After years of just plugging things in and seeing if sound came out (or smoke), I now favor the school that says "replace it." Since modern electrolytic caps are physically much smaller, there's room to mount them under the chassis or "restuff" the old can.

Chris Campbell

Thanks. I was kind of happy to see the discs under there after I had done a little looking into capacitor replacement on older electronics and seeing that wax and paper were commonly used and commonly in need of replacement.

As far as the big can capacitor, I think I’d like to retain the look if that is what “reshuffling” the can would result in. But I don’t know what all is required for that kind of procedure. (But really I don’t know much about replacing anything at this point.)

[SSGNDoc]

There might be a member of the forum who has the schematic you need and would share. Failing that, "The Schematic Man" is a good place, but is not free. He has downloads or you can get the original paper manuals. I personally prefer the original paper manuals, lest there be missing information. You can take it to a office supply store and have a blown-up copy made if you would like. If you have a copy made, you won't wreck the original making notes on it, but you can make notes on the copy without worrying about it. If you put the chassis on a hunk of clean cardboard to work on it, you can use the cardboard for notes without wondering where you put your notebook....

PB Blaster works well to get the gunge off the chassis. You want to be careful wiping the tubes lest you remove the markings.

I’ve ordered a downloadable schematic but still don’t have access to it yet. It may take some searching to finally an original paper copy.

Thanks for the tip on the PB Blaster and wiping of the tubes. I was pretty hesitant to use anything oil based on this since I expect heat and the danger of spark if I do something wrong. That is why, I only did some gentle cleaning and only used water and alcohol to this point. I figured they would evaporate and not be likely to remove markings.

The cardboard is a good suggestion to. Thanks.

[electra225]

Only use PB Blaster on the metal chassis. Spritz a dab of it on a rag then wipe. Don't use it on the tube's. When they get hot, it will stink.

[Hi-Fi-Mogul]

I was kind of happy to see the discs under there after I had done a little looking into capacitor replacement on older electronics and seeing that wax and paper were commonly used and commonly in need of replacement.

As far as the big can capacitor, I think I’d like to retain the look if that is what “reshuffling” the can would result in. But I don’t know what all is required for that kind of procedure. (But really I don’t know much about replacing anything at this point.)

I recommend you go over to "Getting Started" section, where there are lots
of resources you might use.

Also, when cleaning the chassis, be aware there may be cadmium oxides
that appear as white or green/yellow coatings.
Cadmium is a heavy metal you don't want to inhale or eat.

I'd do the cleaning outside in a garage or such.

Use disposable gloves for the cleaning, which I assume you already are.

[SSGNDoc]

Thanks again for the tips. Yes I do wear disposable gloves while cleaning.

I did some looking into capacitor restuffing, and I probably won’t go that route.