Tandberg TD 20A no sound from tape.

[GregoryC]

Hello
I have a problem with Tandberg TD20A. Reels are spinning. Left and right scrolling works. Play works but there is no sound on the output and in the headphones. VU meter is stationary. Switched to Tape. Fuse all are working. Where to look for the fault? Maybe you have an idea where to look and what to check?

 

[GregoryC]

Electrically everything seems to be fine. I connected the headphones and silence. As if the pream was in muting mode.

 

[GregoryC]

Is eprom only for logic or does it affect the preamp?
I apply a signal to the input in recording mode and there is also no reaction.

 

[tapepath]

I believe the eprom is only part of the transport's operation, not the audio circuitry. Since both channels are not working it is a good bet there is a power supply issue. There are two voltage regulators located on the underside of the audio board near the left and right edges of the PCB. You will need to do some DC voltage measurements to see if they are working. Also check to make sure the audio playback PCB is properly connected to the main audio board properly.

 

[Tapetech]

Does source mode work as far as audio signal? To test: connect audio source (like a CD player) to Line IN. Put deck monitor switch to source. You should have audio on Line Out and VU meters should indicate. Also be sure tape is contacting the play head surface and that your tape is not flipped over (wrong side facing the play head)

 

[GregoryC]

I connect a CD source to the line input and there is no sound. VU meters do not work, There is no signal on the output or in the headphones.

 

[Tapetech]

Good to know. So it's not really a tape problem or a playback problem so it's something wrong with your output amp at the very least.

First check that all power supplies in the deck have the correct DC output voltage. The schematic tells you what the DC voltage should be. If all are good, then proceed to signal tracing.

Keep the deck in SOURCE MODE. So now connect a tone generator to the line input and set generator to 1KHz. With a SCOPE PROBE, trace the 1K audio signal from the LINE IN all the way to the LINE OUT. Somewhere along that line you will find exactly where the audio stops. If you don't have the necessary equipment to do this, then take the deck to a technician for repair.

 

[Foxbat]

Are the Sync and Edit switches in their OFF position?

 

[GregoryC]

Yes Sync and Edit is in OFF position

 

[GregoryC]

OK. I found 7824 is damaged. I hope that's the only problem.

 

[Tapetech]

Sometimes a shorted power supply rail can damage a power supply IC (7824)

 

[Foxbat]

OK. I found 7824 is damaged. I hope that's the only problem.

These generally are very reliable chips, but some low cost consumer equipment uses shady brands, to save a dime.

 

[thedudeabides]

These generally are very reliable chips, but some low cost consumer equipment uses shady brands, to save a dime.

Tandberg using a shady brand part to save a dime? The TD20A (decades old) was not a low cost consumer product. Well regarded for quality in its time. I owned one for some 10 years. Used extensively with no issues. Do you even know the brand?

 

[GregoryC]

Tandberg from what I see used very good quality components. The device is over 40 years old. The stabilizer could have been damaged due to age or maybe there is still damage somewhere. It has a temperature as if it was working but at the output it is about 0.4V.

 

[Foxbat]

Do you even know the brand?

I have heard about it.

 

[Foxbat]

Tandberg from what I see used very good quality components. The device is over 40 years old. The stabilizer could have been damaged due to age or maybe there is still damage somewhere. It has a temperature as if it was working but at the output it is about 0.4V.

Time is very important parameters for plastic packages, with moisture getting in. I recently had an interesting experience, when the powered sub on my speakers stopped working. I traced it to an op amp package, and when I touched it its lead came off, exposing the internal construction. And this one was by TI. So no brand is immune, but even good ones can have issues. We once stopped using the batch of National chips due to high failure rate.

 

[Tapetech]

maybe there is still damage somewhere. It has a temperature as if it was working but at the output it is about 0.4V.

And the voltage on the input of the IC is good? Like I already indicated, the rail could be shorted. Have you checked for a shorted rail? Do that before installing a new voltage regulator IC. Remove the IC before checking.

 

[thedudeabides]

Time is very important parameters for plastic packages, with moisture getting in. I recently had an interesting experience, when the powered sub on my speakers stopped working. I traced it to an op amp package, and when I touched it its lead came off, exposing the internal construction. And this one was by TI. So no brand is immune, but even good ones can have issues. We once stopped using the batch of National chips due to high failure rate.

You shouldn't make blind, unsubstantiated claims without cause. You've "heard" about the brand? Good answer. But in these times, that's the norm and truth and integrity have gone down the toilet.

 

[Foxbat]

See... you are soooo easy to get. One carefully selected word sent you into a frenzy. Yes, I have heard about it. Have you?

You see... I have no brand loyalty, I call the shots as I see them. I do have some preferences for this and that, but no blind loyalty.

 

[GregoryC]

Ok. The machine plays. The short circuit was caused by a 1uF/35V tantalum capacitor. Now cleaning the switches and calibrating.