Getting the tape recorder out

[71se3834v]

Did a quick search for a 7 pin din cable and while pleased what I saw was much less than the $69.95 Mopar reproduction ones I didn't see anything other than 9' ones. Not really wanting one as getting the radio/cassette working is way down on the priority list. Nice to know they're out there.

Oh and the bracket on mine was definitely riveted. No way it would just pop off. I had all the nuts off. Maybe some mid year change in design. 😕 The previous owner had bent the tabs where the studs went through to get the original deck out then just laid an Am/Fm cassette in it's place. The one I bought was missing the bracket and top cover when I bought it but it was a floor mount model. Maybe different?
Unfortunately you have to fully remove the deck so you can get at the screws to remove the mount from the console. Can't imagine assembly workers having to install it with all the steps I had to go through to disassemble it.

[Charlie]

So got the tape deck reinstalled... it plays okay.  I think it's dragging slightly... not so bad that I wouldn't listen to it as is.  I'm pretty sure it's due to the belt that I felt was too tight. I believe the belt that runs the FF and REW functions is correct... the 8.6 inch belt. I am going to see if I can get the 10.7 inch belt on ebay. I know I can get it, but whether or not it will get here within typical time frames due to the virus slowing so many things down.

Being a DC motor, there IS a pot for adjusting the speed.  I will first try a different belt, and if that doesn't correct the drag, I will make and adjustment on the speed pot.

Later, after I return from sea again 3 months from now, I am going to remove the pinch roller and send it to Terry's Rubber Rollers in Michigan.  I've used him before for many of my reel-to-reels.  He'll remove the old hardened rubber and replace it with fresh.  Many times, it's better than what the original would have been when it was new.  This would be based on wow & flutter tests results being better than what a unit's original specifications called for.  On a 50 year old tape deck, the end result can be nothing other than an improvement. 

Other than the slight drag and rear speaker not playing, it played pretty decently.  I tried to record from the radio... it didn't do a thing.  Didn't even erase what was on the tape previously.  I will have to check to see if the switch that looks for the tab in the top of the tape cartridge is functioning.   But then, I'm not really worried about recording.

Overall, I am pleased at this point.

[Charlie]

Got the new larger belt in the mail and installed in the deck. Plays a lot better now! I also discovered that the reason the deck would not record was due to a mechanical issue. When you press the button in prior to engaging the tape, a switch engages to change over from play to record. I found the button wasn't going in far enough. I tried loosening the button/knob to reposition it to allow for more travel, and was just barely able to get it to work. Surprisingly, the deck recorded off the radio fairly well. I still have some capacitors to change out in the deck, but will save that for another day. It's pretty good right now.

But with the radio, I've been pulling my hair out to try and figure out why the rear speaker wouldn't play. I changed a lot of transistors and capacitors... and still no rear speaker.

I kept studying the schematics and figured there was something simple I was missing... and wow... was I right! I was missing something! At least, the radio itself was missing something... a resistor! I am looking at these pictures, and then looking in the radio... and start to realize "hey isn't there supposed to be something in that spot?" Come to find out, each channel has a 2 watt resistor between the 12 volt source and emitter of the final output transistor. But in MY radio, one of them was missing, and from what I could tell, one had never been installed!

The resistor value is only about a half-ohm, but it's a PTC resistor... positive temperature coefficient resistor...which means the resistance increases as the temperature of the resistor increases. Problem is... I don't know what it increases to. I just know that it starts out about a half ohm.

For giggles, I installed a plain carbon resistor... 5 ohms at 2 watts... and holy crap... the speaker came on when I turned the key on! Oddly, there was still no music, but it still came on... you could hear the pop... when previously it was dead to the world!

I cannot keep that in there, though. Gets too hot. the circuit does not appreciate a plain-ole carbon resistor. In fact, it got hot enough to melt a plastic cap cover that was right next to it!

So now I know I need to get another resistor, but, they don't really sell resistors of this style any more. At least, I haven't found any yet. I'm afraid I will have to find another radio like this one and rob Peter to pay Paul. Problem with that is... finding AM radios that pair up with the tape deck isn't as easy as ones that do not pair up with the tape deck. The plain AM radio has a completely different set-up inside, and from what I could tell, does not use that resistor. I could likely find it in an AM/FM radio, but geez, they want too much for those... even NOT working (or as they put it... untested).

I'm just surprised the resistor in this radio was missing. So this means the rear speaker in this car NEVER worked? At least now I am not pulling my hair out as much as I was LAST week with this thing!

Makes me wonder how this got past quality control!

[Admin]

[hanks73340]

Thats hilarious!

[71se3834v]

I don't know Dave, that first one looks pretty efficient. I'm all about efficiency!

Too bad your so far away Charlie. I'd offer up my radio for experimentation. It's not plugged in anyway. No rear speaker, the front is probably toast, cassette has no belts, no connecting cable and no plans to fix it. Hearing tunes from a 1970 AM radio is very low on the list.

[Charlie]

Apr 7, 2020 21:25:52 GMT -5 71se3834v said:

Hearing tunes from a 1970 AM radio is very low on the list.

Unfortunately, there are no tunes in my area on AM. Everything it talk/sports radio. And really, we have very few stations. Going to Houston gives a little more selection. Shreveport, Louisiana has a good country station, but I can only get that at night on my radios in the house.

I've been using one of those cassette adapters and it plugs into my phone... and found that listening to my phone's tunes thru the car's old system actually sounds pretty decent... even though I am currently only listening thru the front speaker.

I have been considering one of those new stereos with modern guts that looks like the original... but dammit they're like 600 bucks! Initially, I didn't want one due to having the tape deck option. But after thinking about it, and after studying the schematic, I can just make a special cable for plugging into the inputs of the new stereo.

Since my car sports a rear defroster, I am not able to put another speaker back there on the passenger side.

[Charlie]

So here it is many months later... I FINALLY got my radio working correctly! Well, sorta.  After a lot of changing parts around, I eventually ended up with another radio just like mine being installed.  I got one for parts (not at a cheap price) and robbed Peter to pay Paul.  As you will recall, mine was missing a PTC resistor in one channel.  

Before tearing things apart, I wired up the parts radio to see if it worked at all.  It did... but was extremely weak.  I pulled the resistor I needed and put in my original radio and re-installed in the car.  When I turned on the switch, I heard the rear speaker pop, but no audio.  Then 5 seconds later smoke started coming from the radio.  Damn!  That resistor was over heating.  Something else was buggy in there... a short or a ground.  So I pulled it back out.  I decided not to try tracing down the gremlin causing the problem.  I had already rebuilt the amps in the radio.  Now I was going to have to pull all that work out of there and put in the parts set... so I did.  In that process, I found the reason for the parts radio being weak... two .47 mfd electrolytics were shot.  Got everything renewed in the amplifiers that put her in the car... PRESTO!  Radio works like a champ now... both channels!

Unfortunately, the tape deck is only playing with one channel.  Okay, I'll dig around in there and hopefully find why the other channel doesn't play.  I need to take it apart anyway.  I am planning to remove the pinch roller and send to Terry's Rubber Rollers to have new rubber put on there.  That will improve it's performance.  At least for now, I got both front and rear channels going from the radio.

The rear speaker rattled a little, so I took it out and found little tiny bits of the rear package tray in there.  Brought the speaker in the house (it's the original Mopar speaker) and decided it would not last for long.  The cone was in surprisingly decent shape, but could tell it was very dry and fragile.  There were a few tiny tears.  I got some tacky craft glue and mixed up a 1:1 ratio of glue and water... stirred it up for a while and then cautiously brushed it onto the speaker cone.  The mixture is thin enough that it will soak into the paper cone.  After an hour, I put a second coat on there.  It will dry kinda rubbery and still be flexible since I thinned it with water and should hold the cone altogether.  Re-installed the speaker and sounds great now!

[DynoDave]

Excellent detective work Charlie! Electronics, even dated ones, are just something I'm not capable of working on. Pretty impressive to me that you can do that yourself.

And I like your speaker cone fix too.

I had to do a similar thing with my Trans Am. The twin factory subs had good cones, but failed surrounds. The foam had just rotted away. Fortunately replacements are available.