Jaguar with no sound, replaced U38, reg1 and all caps, still no sound?

[the Goat]

I have a Jaguar console I'm trying to repair. The previous owner used the wrong power supply and damaged U38. I replaced U38, reg1 and all the electrolytic capacitors. The console works now except for no sound output. I do not see any further physical damage.

 

Any suggestions for how I can fix the sound?

[+Stephen Moss]

Presumably you are not getting sound on either the booth screen or the game, if just the game check it sound settings otherwise you might have a blown U4 (TDA1308T) You could try measuring the voltage between pin 4 (GND) and pins 1 (Right) and 7 (Left) but measuring audio with a DMM is not easy however if you get a permanant 0V or 5V reading when you should be getting audio, i.e. during the tumbling letters that is probably a good indicator that either mute is active or U4 may be blown.

 

Consequently, it would also be worth checking the voltage between pins 7 & 13 of U10 to ensure mute is not active 0V = Mute, 5V = Sound.

[Knud]

I had a problem with two of my 14 crt using RF, but worked fine on my 55 LCD. When i got the RCA cable for the Jag i had no problem. Just throwin it out there since i do not know how you are connecting it.

[Zerosquare]

Check the output voltage for REG1.

[the Goat]

I did some probing with my DMM. There was only about 0.7V input on REG1 and 0V output. So that explains the no sound. I also noticed C40 is not populated.

 

Now the power switch seems to have died. I only get power for half a second when I click it on. Then the LED goes out . If I cycle the switch off and on I'll only get another half a second of power.

 

Is the Jaguar power switch know to go bad?

[the Goat]

Also, for completionist sake, I am using an AV cable to connect video and sound. I removed the RF output from this Jaguar. So I cannot test that ti see if it has sound. The AV cable audio functionality has been verified with another Jaguar.

[Gummy Bear]

Did it work before you removed the RF modulator?

[Hyper_Eye]

I did some probing with my DMM. There was only about 0.7V input on REG1 and 0V output. So that explains the no sound. I also noticed C40 is not populated.

 

Now the power switch seems to have died. I only get power for half a second when I click it on. Then the LED goes out . If I cycle the switch off and on I'll only get another half a second of power.

 

Is the Jaguar power switch know to go bad?

 

You have a cartridge in it right? The Jag only powers on when a cartridge is inserted.

[+Stephen Moss]

I did some probing with my DMM. There was only about 0.7V input on REG1 and 0V output. So that explains the no sound. I also noticed C40 is not populated.

 

Now the power switch seems to have died. I only get power for half a second when I click it on. Then the LED goes out . If I cycle the switch off and on I'll only get another half a second of power.

 

Is the Jaguar power switch know to go bad?

On my schematic C40 looks like a high frequency decouple cap across the supply to REG1, I cannot see why its omission would cause any real problems.

What voltage to you reading at the power connector when the input to REG 1 is 0.7v?

 

Power switches have been known to go bad but the switch is simple enough to check.

With the power unit disconnected the switch has two rows of 3 pins, in the Off position two pins on each row should be continuously connected (reading close to 0 ohms) and have no connection to the third. In the On position one of the previously connected pins will be continuously connected to the previous unconnected third pin and the other previously connected will be disconnected from the other two.

If that is what you are getting then the switch is probably OK and you problem lies elsewhere.

[the Goat]

On my schematic C40 looks like a high frequency decouple cap across the supply to REG1, I cannot see why its omission would cause any real problems.

Yes, I agree. I I don't think the non populated C40 has anything to do with the missing sound.

 

Power switches have been known to go bad but the switch is simple enough to check.

With the power unit disconnected the switch has two rows of 3 pins, in the Off position two pins on each row should be continuously connected (reading close to 0 ohms) and have no connection to the third. In the On position one of the previously connected pins will be continuously connected to the previous unconnected third pin and the other previously connected will be disconnected from the other two.

If that is what you are getting then the switch is probably OK and you problem lies elsewhere.

One side of the switch (pins 1, 2, 3) seems to work as intended. Closed pins show less than an Ohm. The other side of the switch (pins 4, 5, 6) is no good. All resistances are in the MegaOhms or open circuit range. Edited March 21, 2019 by the Goat

[the Goat]

Did it work before you removed the RF modulator?

Negative. I purchased it knowing it was broken. Clearly the former owner plugged in the wrong power supply as U38 was completely fried when I got it.

[Zerosquare]

Yes, I agree. I I don't think the non populated C40 has anything to do with the missing sound.

 

One side of the switch (pins 1, 2, 3) seems to work as intended. Closed pins show less than an Ohm. The other side of the switch (pins 4, 5, 6) is no good. All resistances are in the MegaOhms or open circuit range.

Bingo. Half of the switch controls the main power supply, the other half controls the audio power supply.

Bypassing the non-working half with a bit of wire should work for testing.

[the Goat]

Bingo. Half of the switch controls the main power supply, the other half controls the audio power supply.

Bypassing the non-working half with a bit of wire should work for testing.

I replaced the main power switch. REG1 is outputting five Volts and I hear some audio noise when I turn on the power. So I am certain I fixed the audio issue.

 

But the Jaguar is no longer powering on. Arghhh! This is ridiculously frustrating. The main switch Ohms out fine on both sides. I'll have to make some DMM measurements on the U38 side once I calm down. Right now I'm liable to douse this thing in lighter fluid and put it out of my misery.

[the Goat]

One of the pins on U38 was making intermittent contact due to PCB damage when the original U38 fried. I added a bypass wire and now everything is working.

[Gummy Bear]

Yay!