Motorola 57CS - Crashing thunder sound - GO AWAY

 

This is a lovely seafoam green Motorola. I love the porthole design and wild colors! I like the heavy urea bakelite-like plastic Motorola used in the late fifties. The only problem is the material is brittle and tends to crack with changes in temperature. As a result these old Motorolas typically have heat cracks on top. Bummer man.

This particular radio also had the dreaded "silver migration disease," which sounds like a loud crashing static sound. Not to be confused with filter capacitor hum. Silver migration occurs in the Intermediate Frequency Transformer (IFT). A lot of these radios from this period typically have two of these. They look like rectangular aluminum metal canisters. They're hard replacements to find. They are even harder to repair or rebuild. Not fun.

Here's what silver migration disease sounds like:

https://www.youtube.com/watch?v=ggWTcU5oc9w

How does it sound?

It looked like someone once tried to dicker with this radio in an effort save it. I could see signs of numerous disassembly and assembly attempts. I did not see any tampering or component replacement which is a good sign. Don't guess what might be wrong if you aren't sure! Don't start replacing components or re-wire anything unless your measurement instruments tell you it needs to be replaced. Remember, you may not be the last person to try to perform a repair on this radio. The next person, who's hopefully qualified, will have a very difficult time trying to undo bad repairs.

So, I opened this radio up and see the typical layer of dust.

 

Nothing out of the ordinary. I'm not running for the hills yet.

 

So, which IFT is dead? My guess is the one on the left. From my experience, I know the second stage IFT in these old Motorola 57CS's go first (that's the one on the left).

Here's what it looks like all taken apart. The cabinet is separated from electronics at this point because it has an appointment with a bar of soap and a scrub pad:

Next, carefully remove the old IFT and put in the new one. Be careful to put it in correctly. Otherwise, the radio will just hum. You need to follow the circuit diagram and know which loop is the primary and which loop is the secondary. Use an ohmmeter to measure. Do not open the canister. The little wires are as thin as a human hair. If you damage the windings, you've had it. Here is the old one removed and disassembled for viewing:

You can't see the silver migration. The problem is the paper thin sheet of mica that's underneath the base circuit board (brown board at the base of the wiring tube above. The mica will show black spot where electron flow has basically burn a hole through allowing current to pass from mixer stage to pre-amp stage, breaking through the isolation path accomplished by the IFT.

New IFT installed and whoo hoo - Sounds Great!

At this point, if the sound was still crashing static, I would simply replace the first stage IFT, the one on the right. I wouldn't normally bother removing the second stage already replaced. Too much circuit repair causes more problems. Be careful to check you solder connection on both sides of these old Motorola circuit boards. They're double sided! What a nightmare to troubleshoot!

After a little tuning, static-y crashing sound GO AWAY. Here's what it sounds like:

https://www.youtube.com/watch?v=hM9K6bKvyQ8

Like it?

Now, the filthy cabinet and parts are back from the spa. This old radio looked like it smoked two packs of cigarettes a day because it was covered in a black film. Blah. Washed right off with some soap and water. I wish I could say the same for the original owner's lungs. No smell however. Looks clean and fresh:

I chose not replace the filter capacitor on this one because I did not hear any hum. Plus, reference above hassle with double sided circuit boards.I did, however, decide to replace this paper and metal film capacitor because I've seen them blow up.

Now, for the heat crack. Not for the inexperienced or the color blind. Here is that crack. Not that bad. I considered leaving it, but decided fill and repaint to restore the top to its original pristine condition.

This next part is proprietary. I'm going to keep this as a trade secret.

Here's the end result:

 

I'm sure if you were to inspect the restored area carefully, you would see evidence of repair work. I'm sure there are more than a few experts out there who think they could do a much better job. Or, that I should leave the original heat crack unrepaired. However, if you would not have otherwise noticed the repair unless I pointed it out specifically and/or showed you the exact repair location, then I have accomplished my goal.

This radio came with a crack clear clock dial. No way to repair this, that I know of. Does anyone have any ideas? My only alternative is to replace this part if I have one on hand.

finis