Smoked AM Radio

I wish it was smoked HAM, but like the title suggests, I experienced a smoke discharge from a 1972 vintage IH AM radio today. All I was trying to do was identify which terminal was + and which was - on the replacement 4"x8" dash speaker as they were unmarked. The original speaker was badly sun-rotted and crumbling like a dry leaf. I sourced a non-IH, yet vintage 4"x8" speaker that looks to be in great condition. The terminals on the speaker were oriented differently than the stock speaker, so the factory two-prong plug wouldn't connect directly to the speaker. So I made jumper wires from the factory harness to the replacement speaker terminals. I switched the IGN to ACC and turned the radio power dial ON. I could see that the small light bulb inside the radio was lit. I then began touching my jumper wires to the speaker terminals hoping to get some noise out of the speaker. That's when I saw and smelled smoke wafting out of every orifice of the radio chassis. I shut everything down, but it was too late. The old radio smells of crisp bacon and is deader than the hubs of hell. This all happened very quickly. I'd say the radio was powered for roughly one minute before all hell broke loose.
Now to my questions...Can powering one of these old radios with no speaker connected, even briefly, burn them up? Or was it just time for this old radio to go mammaries-up? Has anyone had a similar experience?

 

AM? Seriously? Bout as old as me and eight track tapes. Just kidding

I'm no electrical expert, But it just might be that the radio was on it's way out ahead of time. I've never had or heard of a radio go up in smoke for not having any form of speaker hooked up. Something may have been loose enough to be shorted out in side while being worked on.
BTW - hi Trevor

 

I have the same original AM radio in my '72. Fortunately it still works great - if you can call rotary dial tuning and listening only to AM radio great. I've seen them advertised on eBay, etc relatively cheap if you want to replace it and stay stock. Not sure if you're concerned about maintaining the dash and radio looking original - but there are a few companies who retrofit the guts of vintage car old radios like these, adding FM stereo, bluetooth, etc. but the look remains absolutely original. I'm considering doing that little trick to mine. Last time I checked, you can get it done for under $200. I'm only planning to do it because I hate to put a flashy 2015 stereo in the middle of my 1972 dash.

 

Yep probably a bunch of cobwebs and dust , bridging things that shouldn't be bridged Had that happen
on pops 59 ford retractable ---of course it was my fault --somehow

 

Electrolytic capacitors will eventually dry out and not function, but are easily tested and replaced. Unlike modern circuit boards with surface mounted micro-components, it should be fairly easy to test these and other larger components like diodes, but for most such testing, one really needs to understand circuit design....meaning have a good friend with the ability if you don't. However, you might be able to see what gave up the smoke, just by looking inside the box. BTW, I wouldn't expect an inline fuse in the internal power wire, but the circuit to the radio may have one.

 

Thanks for weighing in guys. Hi Kimball. Full disclosure. This isn't my rig. I've been hired to care take it and fix things that need fixing, mostly under the hood. If it was mine, I wouldn't think twice about moving in an aftermarket direction for the sound system. This whole speaker switch out was my attempt at some added value since I already had the dash pad off anyway. I figured why put it back over a rotten speaker if I could source a reasonable replacement to throw under there first, which I did. My intentions were good, but sometimes good deeds just won't go unpunished. Hopefully, the owner won't be that concerned and will just let it go at that. I don't really want to fall any further down this stock radio rabbit hole if I can avoid it. I was just curious if anyone knew if having this radio powered with no speaker connected could create enough of a resistance imbalance to make it go all Cheech and Chong on me in short order. I know that's not a problem with more modern decks, but this old skule tech is a different animal.

 

No, it shouldn't with this old design. Shorting the speaker lead to a hot wire might, but even grounding the leads shouldn't for a short time. If other, solid state, components are on the verge of failing, any little system imbalance might trigger it though. If you're curious, try googling something like this:

Failure mode of solid state components​

As added anecdotal evidence, my OE speaker is hooked up to a switch so a CB radio can play over the in-dash speaker, and occasionally this has been done while the OE radio was left on. Never a problem with it. Sending on a CB or other modern transmitting radio without an antenna is a different story, I'm told, due to the added power involved.

 

Thanks Dana. I was careful not to let the exposed and energized speaker leads contact any surface other than the speaker terminals. I'll just tell the owner that I don't know what caused the failure, that I don't think it was anything I did, but there's also no way of fully absolving myself, short of involving Grisolm and the rest of the gang at CSI. If he wants me to work with him on a replacement, I can meet him part way. To tie back in with something you mentioned earlier...no there is no inline fusing for these stock devices, just the little 4A fuse in the fuse block, which was present and did not blow during this unfortunate event.

 

Hi Dennis. I couldn't see any polarity markings on this speaker and I looked hard for them. That's why I was embarking on this "touchy feely" expedition. I never heard so much as faint static either way I touched the wires to the terminals and the volume was up plenty. In fact I barely had enough time to try the wires both ways before the BBQ hit full stride.

 

That has to do with whether the speaker cone moves inward or outward with a current pulse. If two speakers are hooked up backwards wrt each other, it causes noise cancelling in some locations. The situation is even more complex than that, but .... isn't life too complicated to ever be boring?

 

I'm not 100% sure about speaker polarity on a DC powered radio, (IIRC the smaller prong is -) but I have some factory radio service sheets for vehicles with tube or early transistor entertainment, say never to power an amp/radio with no speakers hooked up. Then there's the stories of those who did it with no effect, but with what vintage? Safe to say for our old iron, no speaker probably killed it or at least pushed it over.

 

The speaker can work with reversed polarity just fine..ideally you want speaker cone to push out and not a suck back...what is critical is an 8 to 10ohm spkr..4 ohm will damage older transistor radios specifically amp transister...quarter looking dillo in heat sink..your radio being old could require the correct ohm spkr..i dunno..go over to turnswitch.com and read up..post pic of bbq radio

 

Well that sucks. I'm going to blame it on Sailor Jerry and see how far that gets me.

I can't say for certain what resistance this speaker has, but clearly it is an old ass speaker, my best guess is it likely is within the 8-10 ohm range. Its nestled comfortably under the dash pad which I'm not planning on removing any time soon. I'm back under the hood of this rig where I belong. The radio looks fine from the outside. I know the damage would be revealed by opening it up, but that's well down the list of priorities. I tried to do a solid. It should have been simple and straight-forward, but I managed to botch it. I'm done playing with old ass radios and speakers for awhile. There's real wrench turning to be done. Thanks all for your input.

 

blame it on Sailor Jerry
I left yore Mayben/Jerry shop video on the computer at my last job Jus' hope the new guy enjoys it too. I must say it was well done! Onna side note, where's the quote function on this new fangled editor?

 

Jerry lernt me up guder on menee thangz inkloodn how tuh kwote a fuller hoo dun poastid ahed of yersef. See wut ya do iz, ya muv yer lil pointee deal over tuh the buttn wut sez "reeply" under the poast that yer wantin' tuh kwote. Kleer az mud?

 

If you highlight text in a post you want to quote from, a 'quote' symbol appears below on the right; click on it and the highlighted text will open (as a quote) in a reply window. Or, if you have a reply window open, highlight the text you pasted on, click on the 'insert' symbol in the command boxes above, the one that looks like a flag to left of the 'camera', and 'quote' symbols will appear around the pasted text.

 

Okay, I wunderrd wat that dealy bob was fur

 

Got it, and now I see the look to see befor'in I post iz hiddun under opshuns. (Preview)