Ts4d Motorola
 

There is a component marked cr-1 it's rectangular with 4 legs and is mounted between the audio amp and output tubes. Is this a dual capacitor or a resistor array, I can't find a schematic with the parts list to identify it. Still trying to find out what's wrong with the audio why it's got a hum. From what I found is that the ts4d was the only chassis that had this component.

Timmy,
That CR-1 is a capacitor- resistor array as you suspect. The parts are listed as 4 individual components ; C-145 a 0.1 mf, C-144 a 250mmf, R-120 a 250k, and R-121 a 500k . A company named Centralab may have produced that array . If you suspect a faulty component then, you may have to make up your own replacement array.
Ed

We'll unfortunately moyers says there is no listing by cr-1 in centralab so either I make it up or maybe find a SAMs with the parts listing with numbers that maybe moyers can use to maybe find one. Got a hum in the audio and can't find anything wrong so I'm at this array maybe possibly it's bad.

Is it original to the set ? I don't recall ever seeing a part like that in any TS-4 chassis revision

Yes it is original it shows it on the schematic only on ETF .

Download the original Motorola service info from the ETF.

http://www.earlytelevision.org/pdf/m...svc_manual.pdf

It has detailed service info on the early chassis revisions. Here's a portion of the TS-4D showing the couplate values.

https://farm1.staticflickr.com/795/4...6df9c3d8_c.jpg

Don't look for the exact part, make a new one out of good new parts...Original couplates can be a nightmare to source, and if the original is bad there is no guarantee NOS will be good.

Well I really don't know if this couplate is even bad since the audio is loud and clear just has the hum with it. I can't find a possible way AC can get into to audio via a bad couplate. If AC was on the + or - and it's affecting the audio with a hum then it should affect other areas of the set like the picture quality , maybe hum bars , but there's nothing.

This is where the method of *Process Of Elimination* comes in handy. What i would suggest is to disconnect what is connected to pin 2 on V7 (6SQ7) & then power up the set & see if you still have hum. there should be silence. if the hum stops, You can eliminate the audio amp & output stage as being the problem. the problem then, would be somewhere upstream in the I.F. or in the audio detector stages. If the hum is still there, there is a problem with the source voltage from the B++ rail that supplies the audio amp stage.

Are you sure that the hum is a 60 cycle ripple, & not a buzz caused by sync pulses?

Well it sure does sound like 60 hz it's sure loud enough and don't sound like a buzz but rather 60 hz .

Ok, have you tried to remove the leads on pin 2 of the 6SQ7?
the only things i can think of is there is a filament to cathode leakage on ether of the 6SQ7 or the audio output tube, or high ripple on ether the B+ or B++ sources. it also could be originating at the volume control itself (broken ground connection).
if you had a scope, you could trace the audio signal path to the point where the AC ripple is coming from.

Ok clipped all on pin 2 of the 6sq7 and still got the hum, so I guess it's off to the b+ or b++ . Ground at the volume is intact.

Ok. If you replaced that 20 mfd capacitor off of pin 8 of the 25L6, did you connect the negative end of it to the same tie point as the original was?, or did you attach to the closest chassis ground?
the reason why i ask this is because the grounding for the entire audio is isolated from the chassis & connected to the B- rail. If you connected the negative of that capacitor to chassis, that could be the problem.
regarding the volume control, if the ground connection on the wafer in the control is open, it can cause the same problem. you need to disconnect the leads off the volume pot & check for end to end continuity, as well as continuity between the wiper contact as it is moved from one end to the other. i have seem many bad pots cause this problem.

That 20mf ground is ok it's not on the chassis, I know there are the 2 grounds, chassis and b- . I'll check the volume ground, via the wafer. Thanks

Ok the volume control checks out, wiper to end does vary the way it supposed to. So now still at dead end, I even tried other diodes thinking one may be leaky but no luck there and I also paralled every cap still no luck still hums. The Motorola Manuel showed reasons for a hum and I checked that out still no luck. When I first got the set I had to tweek the IF for a clear pic and sound and the Manuel says if the oscillator is adjusted to high it's considered to be overloading and the audio would get a 60 hz hum carried along the verticle circuit, strange, hmmm. Checked around the verticle to no avail. What I also tried was I turned the 3 adjustments L17 ,L19 , L27 4 turns cw then 4 cww to see if that made a difference in the hum if that were the reason but I never did turn them a lot in the beginning.

Do you still measure a high voltage between the chassis and b- ?

jr

No hv neg to chassis I obviously went from b+ to chassis. My mistake.

What do you hear if you disconnect the grid (pin 2) of the 25L6 audio output tube.

jr

I didn't disconnect anything else but pin 2 of the 6sq7, still humming.

So now i'm asking what happens if you repeat the experiment on the next (last) audio stage. :scratch2:

jr

Are the filaments in series, or is it possible to pull the audio amp tube and see what happens to the hum? Do you have a tester to check the audio output tube for heater/cathode short, or a spare output tube?

Well I could take off pin 2 but nothing will happen, heater. Or you meant grid I think ?

I tried 2 other tubes both of them and my tester does check for shorts. It is series.

Yes, grid, pin 5, sorry for the confusion.

jr

Pin 5 off hum even louder with no hiss as if there was no ant.

Interesting.

What happens if you connect pin 5 of the 25L6 to either end of the cathode resistor (330 ohm R-38) ? Try both ends.

jr

After the grid wire was put back on?

Ok, either side of the 330 resistor it blanked out the audio all together.

Well the 330ohm resistor checks at .336k so I have a new 330ohm resistor that checks just that so I'll change that resistor tomorrow. One end of that resistor goes the cap at the amp . maybe it cannot filter because of that resistor being high.

Seems like it coud be leakage from the grid to the heater pins. :scratch2:

Is the socket dirty or perhaps charred? Bad insulation on wire to the grid?

jr

Edit add: Why change a resistor that is only 6 ohms off? That is less than 2% off.

The resistor checks .370 k so that's off a bit from 330 ohm . Befor in another post I said it was .336 k that was incorrect however that didn't fix the hum. This is turning into a mystery.

Did it blank out the hum? If so, the hum originates from the audio circuit. :scratch2:

It blanked out all as if no speaker was connected, or as if it were turned off. If the hum was gone there should have been other noise like a hiss when no antenna connected.

Since that is the last audio stage, there would not be much/any hiss when it's input (the grid) is grounded.

Another experiment... instead of grounding the disconnected grid, insert a 470 k ( or so ) resistor between the grid and either end (try both) of the 330 ohm cathode resistor.

jr

What I did was put the grid back on pin 5 of 25l6 then jumped from the grid to either end of the said 330 ohm resistor, the grid was put back on when I did this and it blanked out so now you want me to use a 470k or so resistor from pin 5 to either end of the 330 ohm resistor while the 330 is still in place, correct? So really it's just raising the value of resistance in that area. Ok I got it, lol between grid and the 330.

Yes, but the grid should be disconnected from the couplate.

jr

Ok grid disconnected 470k from grid to ground side of 330 has hum to the other end of 330 blanked out, silent nothing no hiss.

Is the hum as loud as when the grid is connected to the couplate?

jr

Couplate on , hum, couplate off 470k to the ground end hum is Alittle less 470k to the other end of the 330 blanked out.

I'm still thinking leakage in the tube or socket...
Another experiment: with the grid of the 25L6 totally disconnected, and the set off and unplugged measure resistance between the grid pin (5) and all of the other pins of the socket with and without the tube in the socket. This is turning into a real headscratcher.

jr