1965 Mustang AM radio restoration. 5TMZ.

[daveoverride]

I think the positive ground nature of the transistor is taken care of by plastic membrane and lithium grease in between. The collector communicates with the rest of the radio through two screws and they are commented on the other side to a wire.

I did the test and wrote the result in a table. I'm not too sure how to interpret it. I think toast? (The end of first line means about one second values of about 1700 then drop to OL. The test did was using "diode" setting.

[daveoverride]

Photos

[Cobaltblue]

You don't seem to be adding the attachments.

See Grahams guide Here

https://www.vintage-radio.net/forum/...ad.php?t=77650

Cheers

Mike T

[daveoverride]

One more try to upload, this time lower res.

I heared the big can capacitator may also be culprit because "the electrolyte may dry out and make shorts.

Did i do the measurements correctly? What is the verdict?

[Station X]

Did you test the C-B an B-E junctions both ways ie reverse the meter's leads? That would give four readings.

The case is the collector.

https://pinout.net/element_browse.php?conid=16820

[daveoverride]

I tested c to e, c to b, e to b
Both ways (change of polarity)

- showed in all cases that pair of leads work as diode but between c and e this function got after about second OL reading. Isnt it wierd?

Second: what are your thoughts on capacitator readings?
I have heared two stories that it has something to do with filtering interference from alternator or with speaker signal amplification. If i got readings like 1; 2 or 92 Ohm against the casing of Capacitator does it mean its broken?

[usradcoll1]

Originally Posted by daveoverride

Hi Chris, i agree with what you say!
About me really using AM radio today, not too sure - i remeber last time doing so as i was 8yo and was wondering what could i catch on grandpas old tube radio. But who knows i might discover something.

Id try getting the radio now since costums are bussy with more important things these days. Maybe it would come!

I wish to have the Motorola restored and running just for the feel of it being true original and and possibly even if it fully working add that second secret mp3 radio that would fit in an ashtray or glove box (just in case i wanted to listen to period correct music or even not).

I have to pick up my multimeter and test the transistor next week - ill inform you about the result in detail. Thanks all for posting your knowledge and advice. I am excited about how it will turn out!

I worked on many of that type of Motorola radio. There were many of them around, both OEM and after market.
They were very reliable except for the 2SA72 transistors. I replaced all three with universal replacements, available at the time.
I never found a shorted 2N176 or a bad output transformer. It was probably the early to mid-70's since I worked on one.
Dave, USradcoll1

[Station X]

Originally Posted by daveoverride

I tested c to e, c to b, e to b
Both ways (change of polarity)

- showed in all cases that pair of leads work as diode but between c and e this function got after about second OL reading. Isn't it weird?

Weird or not that transistor is open circuit and therefore useless.

[daveoverride]

Ok that determines that the best way would be the TDA2030 as Chris suggested. I'll go ahead and order couple of units (in case of faliure or later needed).

Regarding the schematics of 5TMZ:
If someone reading have them - please send me or someone from forum a photo.
In case noone would have it i order it next week.

[daveoverride]

The TDA2030 board came and i have ordered shop manual of the radio, will post as soon as it arrives.

[daveoverride]

Any ideas what should i remove and where should i solder the amplifier board?

[daveoverride]

Schematics of the circut

[Herald1360]

Luckily (for ease of modding) the radio is negative earth so no odd signal grounds to contend with.

I'd disconnect the collectors of the audio transistors V4 and V5 to shut the audio stages down leaving the parts in place in case anyone might later go for a restoration rather than repair.

Connect the power + and - to the amp module + to the switched 12V at point 2 and - to the chassis.

Disconnect the + end of C17 from point 21 and connect it to the amp signal input.

Connect the amp signal ground input to the slider of the tone control pot (this is signal ground).

Disconnect the speaker output connector from the output transformer and ground and connect it to the speaker terminals of the amp.

Cross your fingers!

If no magic smoke released and sound is heard, adjust the input level trimmer on the amplifier to give a comfortable noise level when the radio volume control is set to mid travel.

Go cruisin'

[daveoverride]

Hi, thanks for your quick answer.

No smoke came.

I dont think it will be that easy...

Just a reminder output transformer (what i guess it was - the bigest transf. Of all three) same as v5 are history (gone out of circuit).

I conected:

+12 to the vcc

(Same)+ 12 to the circled 2

In to the disconected c12 + end (butchered it a little but no contact of coat to the middle metal part)

First ground as read from left on amp board to the middle leg of potentiometer that changes volume (the correct knob that was changing Ohms as i turned it)

The second ground to the case

And speaker to the green crimp connectors

-------
What it does is:

Amp little red led is still ON, regardless of me turning volume knob all the way to off.

Very faint hiss - only heareable when i lean to the speaker with my ear.

[daveoverride]

Some photos

[daveoverride]

One thing to mention - i havent connected red-blue wire (which im sure is for front radio light bulb) and one other black wire that case and red enameled wire from a transformer on the left

[Herald1360]

Sounds like you've mixed up the slider of the tone control pot with that of the volume control pot for the signal ground connection. The slider of the tone control pot is connected to the anticlockwise (minimum volume) end of the volume control pot- I thought it might be easier to find a slider than one end of a pot since there's only one slider but two ends!


What are the actual labels for the pins on the amp module? I couldn't find any online info as to which was which for power +, power -, signal in and signal grouind.

[daveoverride]

Hi Chris, I will check the tone / volume knobs once more, but i am pretty certain that when i turned the volume knob it was changing resistance measured with multimeter.

About the amp board
VCC IN GND GND


+ - (out)

[daveoverride]

Regardless the faint hiss, i havent been able to tune into anything.

Secondly, isn't the current suppose to go through switch/volume knob prior getting to the anplifier board (fixing the amp ON while radio being OFF)?

[Herald1360]

I think we're talking at cross purposes here- yes moving the volume control slider will vary the resistance between the slider and either end of the volume control but my query was about whether you had connected the signal GND input to the amp to the volume control or tone control slider. The former won't work since you would simply be shorting the volume control slider to ground via the amp, the latter is itself connected to signal ground in the radio and looked like a convenient easily identifiable physical point to connect the amp signal GND.


The amp signal IN is connected to the volume control slider, just via the capacitor C17. That's why I suggested disconnecting C17 from the base of V4 (point 22) first. I chose to do this to avoid any possible dc connection problems between the amp signal IN connection and the radio's signal circuits.


If it's all connected up correctly and there's still no signal it looks like you will need to fault find the RF stages (to the left of the volume control in the circuit) next