Ok. TR417 is toast.
Now check all capacitors, resistors, and zener in-circuit around TR417 and TR419.
Check across C408 and C410.

Can you elaborate on the best way to check these components? Can any be tested in place or should they all be pulled?

 

Firstly, use the ohmmeter and measure the resistance in both directions while the component is in-circuit since this does not require removing the component. From these results we can then make a decision as to whether the component needs to be removed for further testing.

Another reason for testing across C408 in-circuit is because there is could be a short further down the supply chain. This is still to be determined.

If there is no short found across C408, then we leave it alone. If there is a short found, then we remove C408 and test it and we test across the -16V supply rail and ground.

 

Firstly, use the ohmmeter and measure the resistance in both directions while the component is in-circuit since this does not require removing the component. From these results we can then make a decision as to whether the component needs to be removed for further testing.

Another reason for testing across C408 in-circuit is because there is could be a short further down the supply chain. This is still to be determined.

Sounds good. Thanks so much. I'll report back shortly.

 

Firstly, use the ohmmeter and measure the resistance in both directions while the component is in-circuit since this does not require removing the component. From these results we can then make a decision as to whether the component needs to be removed for further testing.

Another reason for testing across C408 in-circuit is because there is could be a short further down the supply chain. This is still to be determined.

If there is no short found across C408, then we leave it alone. If there is a short found, then we remove C408 and test it and we test across the -16V supply rail and ground.

OK, here are some initial measurements. If I've missed any components or you find any others that you think I should check please let me know.

C408: 118.2k ... 63k
C410: 36.8k ... 34.5k
ZD404: 36.4k ... 34.2k
R416: .4k ... .4k
R418: 6.2k ... 6.2k
R442: 10.1k ... 10.1k
R425: 30k ... 30k
R441: 99.6k ... 99.6k

 

Ok. Thanks for the readings. Nothing looks amiss.

Next step is to find a replacement for TR417
2SB1274 PNP power transistor in TO-220 package 60V 3A

You could try TIP32A.

Also get R432 4.7Ω replacement (wattage unknown)
After you have installed a TR417 resplacement, install 100-330Ω for R432 instead of the 4.7Ω for now to test the voltages.
If there is no short circuit then go ahead and install proper 4.7Ω resistor for R432.

 

Also get R432 4.7Ω replacement (wattage unknown)

P/L shows it as 1/4W.

 

I have 2SB1274 transistors in my stock. Shoot me an Email if you want one to keep the parts "original".

Dan

 

Ok. Thanks for the readings. Nothing looks amiss.

Next step is to find a replacement for TR417
2SB1274 PNP power transistor in TO-220 package 60V 3A

You could try TIP32A.

Also get R432 4.7Ω replacement (wattage unknown)
After you have installed a TR417 resplacement, install 100-330Ω for R432 instead of the 4.7Ω for now to test the voltages.
If there is no short circuit then go ahead and install proper 4.7Ω resistor for R432.

Great. I just ordered the transistor. Looks like I have the 1/4 watt resistors on hand.

 

I have 2SB1274 transistors in my stock. Shoot me an Email if you want one to keep the parts "original".

Dan

Sorry, just saw this response in the thread after placing my order. Let me compare what I receive to the one I pulled. If unsure I'll circle-back. Thanks!

 

Ok. Thanks for the readings. Nothing looks amiss.

Next step is to find a replacement for TR417
2SB1274 PNP power transistor in TO-220 package 60V 3A

You could try TIP32A.

Also get R432 4.7Ω replacement (wattage unknown)
After you have installed a TR417 resplacement, install 100-330Ω for R432 instead of the 4.7Ω for now to test the voltages.
If there is no short circuit then go ahead and install proper 4.7Ω resistor for R432.

OK. I got the replacement for TR417 and installed it along with a 330Ω resistor. Powered it up via a dim bulb tester and measured the following . I didn't notice any shorts but there is still no audio.

Base: -13.8v
Collector: -15.7v
Emitter: -13.6v

I don't know if it's helpful or not but for comparison I also took measurements of 413 and recorded the following.

Base: 16v
Collector: 31.8v
Emitter: 17v

I'd like to think we're making progress but I'm not sure.

 

At this point, while working audio would be nice, that is not the focus.
The focus is getting -16V on the power rail at the emitter of TR417.

Ok. Go ahead and install R432, 4.7Ω.
Confirm +16V and -16V supplies. Measure the voltages across R431 and R432 and calculate the two supply currents.

Then it is back to tracing the audio with your powered PC speaker.

 

At this point, while working audio would be nice, that is not the focus.
The focus is getting -16V on the power rail at the emitter of TR417.

Ok. Go ahead and install R432, 4.7Ω.
Confirm +16V and -16V supplies. Measure the voltages across R431 and R432 and calculate the two supply currents.

Then it is back to tracing the audio with your powered PC speaker.

OK, I replaced R432 with the originally specified 4.7Ω resistor. Measurements are as follows. Note: unit still powered via the dim bulb tester.

TR417
Base: -16.2v
Collector: -31.9v
Emitter: -15.6v

R432
-31.9v and -32.2v

R431
31.4v and 31.7v

 

Good. You have 0.3V across both resistors.
That means the current is 0.3V/4.7Ω = 64mA and balanced.
-15.6V looks good compared with the +ve side at +15.8V

In my next post I will see how far you and @drc_567 got with the audio signal tracing.

 

Looking at posts #24, 25, 26, you got audio at CN6A-1 and CN6A-2.

For here on, I am going to guess that the problem lies with one of the following:

IC201, TC9164N
MUTE
IU-2486 motorized volume control
IC251
IC701

I don't know how the VOLUME control works. I have to study the circuit diagram.

Work the front panel and all the controls and let us know what appears to work and what doesn't.
In other words, can you select the various functions, TUNER, VIDEO, TAPE, UP, DOWN, etc?
There appears to be about 20 push-buttons shown in the schematic.

 

I don't recall whether or not I mentioned this in the past, but the TC9164 IC is a common failure point in these units. The easiest way to confirm this is to either scope the pins of the IC itself or to check the tape out connections. Unless the unit is using the tape "system", the tape out should have the source signal on it. If the IC has failed, you often will get no signal on this connector, or the signal if there will always remain the same regardless of the input selected. Check this IC first. (These fail often enough, that I stocked them in rather large quantity, ie 20 or more at a time.)

Dan

 

Looking at posts #24, 25, 26, you got audio at CN6A-1 and CN6A-2.

For here on, I am going to guess that the problem lies with one of the following:

IC201, TC9164N
MUTE
IU-2486 motorized volume control
IC251
IC701

I don't know how the VOLUME control works. I have to study the circuit diagram.

Work the front panel and all the controls and let us know what appears to work and what doesn't.
In other words, can you select the various functions, TUNER, VIDEO, TAPE, UP, DOWN, etc?
There appears to be about 20 push-buttons shown in the schematic.

With respect to the front panel everything appears to function as expected. In other words, other than no audio there doesn't appear to be any change in the way the unit operates:

1. • All source selector buttons work
2. • Both manual and auto tuning work as expected
3. • Saving radio stations to memory works
4. • Selecting between tuning bands works
5. • Motorized volume control works via remote as expected

 

With respect to the front panel everything appears to function as expected. In other words, other than no audio there doesn't appear to be any change in the way the unit operates:

1. • All source selector buttons work
2. • Both manual and auto tuning work as expected
3. • Saving radio stations to memory works
4. • Selecting between tuning bands works
5. • Motorized volume control works via remote as expected

With a defective TC9164, the front panel will appear to switch sources but in fact the source will not be switched. Check with a scope to see if switching actually occurs.

 

but the TC9164 IC is a common failure point in these units

Particularly if TR417 had failed and momentarily overvoltaged the negative supply rail.

 

I don't recall whether or not I mentioned this in the past, but the TC9164 IC is a common failure point in these units. The easiest way to confirm this is to either scope the pins of the IC itself or to check the tape out connections. Unless the unit is using the tape "system", the tape out should have the source signal on it. If the IC has failed, you often will get no signal on this connector, or the signal if there will always remain the same regardless of the input selected. Check this IC first. (These fail often enough, that I stocked them in rather large quantity, ie 20 or more at a time.)

Dan

Unfortunately I don't have a scope but I was able to use the trace cable I constructed to check the pins of TC9164N. I'm not sure if I'm reading the schematic correctly but my assumption is that pins across from each other correspond to the left and right signal. What's interesting is that placing leads across such corresponding pins yields no signal but I do get a signal when I place them across adjacent pins. For instance, one lead on the tuner and one on video in produces a signal with both sources combined. Hopefully this makes sense. Does this confirm that the part is defective? Is there a different or better way to test this part?

Thanks again for all the help!

 

... Can't be absolutely sure, but it looks like the tuner right and left inputs are the fourth pins from the notch end of the chip, one on either side. The output from the tuner is carried through the chip to the third pin on each side, counting from the bottom or opposite end from the notch. What is not clear is if the tape 1 needs to be turned on for the output pins to be activated. Also check the Tape 2 switch, to see what that does.
... It may be that the IC201 output pins, 3rd pins from the bottom, either side, are active when the tuner is turned on, and the Tape switch activations are an option.