Tandbergy fault. What, and is it worth fixing?

[BrizzleBen]

Hello. Post number one here. Hope all compliant.

I have been given a Tandberg amp, the TA 300. Having bought the necessary 7pin DIN to phone adaptors and made 2pin DIN connections for my existing speakers, the first time I've wielded a soldering iron in many years, I find one channel produces no sound.

Here's what I've noted.

swopping the phono inputs left / right makes no difference
selecting "mono" right produces sound on both speakers
selecting "mono" left produces nothing
selecting "stereo" just gives sound to the right.

What does this tell you and what can be done and is it worth doing?

I look forward to your views

Thank you

Brizzle.

[Kvaal]

A common problem on this amp is the switches that doesn't work correct becauce of friction. You can fix this by opening the amp and spray wd-40 in between the alu steering-slides that you see when you look down into the amp. Be careful and use as little as possible. Now that the amp is open, you should spray the switches from the open rear with electrolube or similar cleaner/lubricant for electronic switches/connectors. Do some switching afterwards to make it work.

Another common problem is the output caps. They can dry out becauce of age and use. They must be changed if this is the problem.

[BrizzleBen]

Thanks Kvaal.

I'll try the WD40 trick. Is there a way to test if it's the capacitor and is sourcing a new one going to be a challenge, do you think? And if I find one should i change both and could I fit them myself.

Questions questions.

[shane]

It's not going to be the output caps if both speakers work on mono right, because both power amps must be OK. The fault must be in the phono section, the pre-amp or the switches. Do any of the other inputs work? Can you try plugging a CD player or similar into the tuner input or one of the tape inputs? Are you sure your din-phono adaptor is OK (you did mean 5-pin DIN, not 7-pin, didn't you? :)) You can check by unplugging it with the amp switched on but at a low volume and poking a jewellers screwdriver or something similar into each of the holes in the din socket. Two of the holes should produce a buzz, one from each of the speakers.

Kvaal's right though. Start with the switches.

[istari_knight]

I would try working all of the buttons/switches/controls as many times as you can be bothered. It sounds like a dirty contact [pun intended ;)]

Its usually the one's that never get used such as tape monitor or stereo/mono.

[Kvaal]

Shane is right. It can't be the output caps.

This amp have some followers here in Norway. They claim the phono-section to be of the highest quality. The output section is not of the strongest, so it is poular to match it with small Klipsh-speakers (RB-63). Many norwegian audipphiles use this amp with Dual TT's from the same period, the 1200-series.

[BrizzleBen]

Thank you very much Kvaall, Shane and Istari, Shane you nailed it: plugging the CD into the tuner input gave audio on both left and right in stereo. Phono 1 and Phono 2 work on right only so it's the phono section. So what can be done?

[Kvaal]

One possibility is the din-sockets. Some solderings are not of the best. Re-soldering them can be all you need to do.

[BrizzleBen]

I think I've hit on something.

I thought it must be something common to both phono one and phono 2 so found a circuit diagram on the web which is pretty much greek to me but after much head scratching I noticed that the connections to the 5 pin DIN sockets were different for TUNER and PHONO. Shane had queried whether the DIN plug was the culprit but as it worked on TUNER I'd ruled it out. Looking inside, I see the connections are for TUNER so I'm missing a pin.

I'd specified to the ebay seller that I wanted an input to phono so I'll see if he'll stump up for the right one.

Have to say, I'm hopeful that this will prove to be the problem and that no soldering or repairs will be needed :)

If so, the only remaining question will be, was it worth the effort!

[Kvaal]

The din-norm have different configuration for phono and the other inputs.

[BrizzleBen]

Spoke too soon.

The "missing" pin is irrelevant. The left channel is connected to pin 3. sad face.

[shane]

Just found that schematic here http://sportsbil.com/tandberg/ta-300m-s.pdf and as you say, the tuner and phono sockets are different. Well, they are and they aren't! All three have the conventional layout of earth pin 2, left pin 3 and right pin 5, which is how your adaptor will be wired. The only difference is that the phono sockets will also accept the left input on pin 1, which won't make any difference to you. (that is to allow connection of turntables using the older 3-pin din). All very confusing....

Din wiring is explained here:http://www.electronics2000.co.uk/pin-out/dincon.php (the audio section relates).

Again, the best way to check if the phono inputs are working is to poke a thin piece if metal or wire into each of the holes in the DIN socket in turn. Two of them should produce a buzz, one from each speaker. Try it on both phono sockets and see what happens.

[BrizzleBen]

Thank you for looking out that schematic, Shane, and for the DIN explanation.

I've poked: buzz produced on pin 5 on right channel only, on both phonos 1 and 2. Nothing on pin 3.

Undaunted, I've looked at the sliding switches operated by a push button to select phonos 1 and 2, see picture. They have six copper rods protruding from them and touching some of these on the rear switch produces the same buzz: the middle rod always buzzes on the right speaker as does touching either the front or back rod depending on whether I've selected phono 1 or 2.

I get nothing out of the other switch at the front.

Next to the front switch are two wires connected to push fit terminals identified as R and CH (brown wire) and L and CH (white wire) (See second picture) When either Phono 1 or 2 is selected, touching the R and L terminals produces a buzz on the corresponding speaker. If I select Tuner, there's silence so I guess they're part of the phono section,

Does that tell me anything?

I'm guessing the fault lies before those cables marked L and R because they buzz but whether it's the switch that's faulty or something in between is beyond me.

I like a puzzle :)

[shane]

OK, it's still not clear whether the fault lies in the switch section or the phono pre-amp. The signal goes from the two din sockets to the front and back switches. The output from the switches goes to the phono preamp input. The output of the phono preamp goes to the tuner switch, which swaps between the phono output and the tuner socket to feed to the rest of the amp. What we don't know is whether those two cables carry the signal from the phono switches to the input of the phono preamp, in which case the fault lies in the switches, or from the phono preamp output to the tuner switch, in which case its in the phono preamp. If you can identify the phono input caps c101 and c102 in the phono preamp, select either phono 1 or phono 2 and touch each cap with a finger. If you get a buzz from both channels, the phono preamp is OK and the problem is in the switches. If you don't, then one channel of the phono preamp isn't working.

[BrizzleBen]

Gobsmacked by help.

These'll be the fellas.

Will check 'em out tomorrow.10761

[shane]

That's of 'em, as they say down yer.

[BrizzleBen]

There was probably a certain amount of eye-rolling from upstairs as I produced various humms and buzzes first thing on a Sunday morning, but let's be 'avin' em:

C101
Stereo: buzzes on both channels
Mono R: "
Mono L: "

C102
Stereo: buzzes on right only
Mono R: " on both
Mono L: " on neither

So I've lost a channel on the preamp then?

[shane]

Looks like it, I'm afraid. Don't think I can diagnose the phono preamp itself from here! A bit odd though. On stereo, I'd expect C101 to buzz on the right channel and C102 to be silent. I wouldn't expect either of them to buzz on both channels.

Whatever is wrong with it, it shouldn't be difficult to sort out for someone who knows about these things, it seems like a well made and thought out design, as you'd expect from Tandberg. If you want someone to have a look at it, these people aren't too far away from you and would fall on it with cries of delight! http://www.kselectro.co.uk/index.html

[BrizzleBen]

Thank you again, Shane. I'll get in touch with K & S.

I have a perfectly good amp I'm happy with but the Tandberg is crying out to be brought back into use. Probably because it's more appealing than re-tiling the bathroom.

[shane]

Probably best to drop them an email with a link to this thread. Angela used to post on here (AKA "theoldtrout"), but I think she fell out with Marco over religious differences, not that that's got anything to do with hi-fi....

[jollyfix]

Hi Ben, if i can help in anyway just ask. I live quite close to Barton st David, I am up in London working right now, but hope to be back in 2wks. Then i have to go to Cardiff, so if you take your amp to KS, there is a good chance if the timing works out, i could pick your amp up and drop off to you in Bristol on my way to Cardiff type of thing. Just a thought.
cheers Dave.

[BrizzleBen]

Amazing! I'll PM you contact details. Thank you.

[shane]

Good 'ere, innit? :)

I know what you mean. In the great scheme of things, the TA 300's never going to go down in history as one of the great-sounding amps, and nobody would ever tell you to go out and look for one. In comparison with the best, it probably won't sound that brilliant, but there's an atmosphere to equipment of that era which is completely irresistible to those of us who grew up then.

[jollyfix]

pm sent

[BrizzleBen]

Shane, it is :)