ID this stuck/jammed Cessna 300 nav/com

[Pedals2Paddles]

I was pulling each radio out to note the exact model and serial number this evening. This damn thing won't budge. I loosened the two obvious screws on the top, but can't see anything else to loosen. It will not budge at all.

The unit is inop. The breaker pops as soon as you turn it on. We'd really like to see if it can be quickly and easily repaired. And if not, we need the exact model number to find a TKM slide in replacement (I hope). But I can't get the model number without removing it.

Can anyone suggest how to get this stupid boat anchor out? And/or, can anyone identify the exact model by the picture?

 

[Marauder]

Wow! That has to be a first generation Cessna 300. What year plane is it in? Since they were made for Cessna, you may try searching for the service manual for that year plane. The radios stuff may be in there. I know the old POHs did have the RT-308 and RT-328 information in them.

 

[Marauder]

Another suggestion is to remove the rack above it. Looks like for your picture that the rack is screwed in, not riveted. You may be able to see if something is binding it in place.

 

[Pilawt]

Wow! That has to be a first generation Cessna 300. What year plane is it in? Since they were made for Cessna, you may try searching for the service manual for that year plane. The radios stuff may be in there. I know the old POHs did have the RT-308 and RT-328 information in them.

That's the style that was installed in new Cessnas in the 1967 model year only. '68 had a flat faceplate.

The photo below was a '67 C-172H with less than 80 hours since new.

 

[Henning]

How do the catches work? Do they screw the back or use a latching coupler? Have you tried a hammer on the top yet? Start with a nylon face 2oz and work your way up to the 32oz dead blow ball peen. Sometime smacking the face pops them loose.

Repair that radio? Seriously? You can probably find a TKM on eBay cheaper.

 

[Marauder]

That's the style that was installed in new Cessnas in the 1967 model year only. '68 had a flat faceplate.

Thanks for the additional information. Is it possible there are a set of screws under the lower knobs? Pilawt's picture shows something shiny under the lower left knob.

 

[Henning]

Thanks for the additional information. Is it possible there are a set of screws under the lower knobs? Pilawt's picture shows something shiny under the lower left knob.

Anything is possible, may as well just pull the knobs and see.

 

[Pilawt]

This photo is blurred and doesn't really provide any more useful information. But that model radio brings back memories, because it was the one I used most often in my student pilot days. I took this photo in a then-new '67 C-150G.

 

[nrpetersen]

Does it move at all? There may be something at the rear that is custom. Looks like it has been out many times. What an antique!

 

[James331]

Get a pair of pliers and a blow torch and get medevil on that radio lol

 

[wanttaja]

Ok, I don't have that model of the Cessna 300, but it's probably similar to the one you're having problems with.

Note the image below. The two screw heads at the top of the case are used to hold the radio in the rack, but they don't really thread into anything. There's a plastic cam on the end of the screw, and turning the head rotates the cam (the one on the right is missing the cam). The cams hold the radio tightly in place by turning until they engage the square holes at the top of the picture. Then continued turning of the screws tightens the radio in place.

So....you need to loosen the screws until there's no tension on the bolt, then position both screws to get the plastic cam out of the slot. From your picture, you should be able to see if the cams are clear of the slot.

It's possible the cams on your radio are jammed, somehow. In that case, you can probably slip a big screwdriver into the cam slots and bend them up a bit for more clearance.

Ron Wanttaja

 

[Pedals2Paddles]

OK, the screws are loose but don't seem to be disengaging the cams. They just spin freely. So I guess next I'll unbolt and push back the tray above it to access the cams.

Anyone know the exact model # of this thing?

I'm not holding my breath on bring this thing back into an operational state. But a small part of me is hoping to see a little loose wire on the back, and it will just start working again...

 

[pmanton]

Is it even legal? It looks like a 360 channel radio

 

[Pedals2Paddles]

Probably not. But if a loose wire fixes it, I'll be happy to just listen to the WX with com 2. We have a KX155 for primary nav/com. When the $$ presents itself, I'd like to put an MX300 in it's place if they have a slide-in replacement.

 

[Graueradler]

If I remember the discussions from several years ago correctly, it is legal to continue using but not legal for a repair shop to fix it when it breaks.

If the breaker pops as soon as you power it up, I'd look for a failed electrolytic capacitor. On mothballed ships, where the radios had been de-energized for a long time, we would just keep feeding them fuses until the electrolytics rebuilt a film and stopped drawing so much current.

 

[flyingron]

If I remember the discussions from several years ago correctly, it is legal to continue using but not legal for a repair shop to fix it when it breaks.

You are not remembering correctly. It's illegal to TRAMSMIT with these PERIOD after Jan 1 1997.

Technically it is not the 360 channels that's the issue but the 30 ppm frequency tolerance. All the 720/760 channel radios meet this, but some of the 360s do as well. Alas this boat anchor does not. The FCC allows you to keep these for receive or "antique display" purposes as long as you don't transmit with them.

As suggested, your best bet is probably to remove the tray above and pry the top of the 300 rack to clear the cams.