Anyone familiar with the Tandberg 3002 preamp?

[JohnMac]

Alrighty. I cleaned all controls and switches. Phono sounds nice. However one channel has very little output when in stereo. When I switch to mono they are equal. I switched source and amp interconnects to eliminate problems there. Any ideas?

I quess I should try aux to see if the problem is there too.

Add on: Aux is fine. I switched to the MC inputs and it works fine there but I'm using a MM cart???

I was going to take it to a tech that I know but decided to give it one more look.

First I checked all of the resistors in the phono section. They were all in spec. One bad resistor wouldn't have made sense anyway because the problem was in both channels.

Turns out there were two problems. I noticed that when flipping the selector knob from aux to phono the output would cut in and out. I re-cleaned the control and one channel kicked in. Then I wiggled the caps while it was running and got some static on the bad channel. Sure enough there was a bad solder joint.

Not a very high tech approach but it 's fixed and I saved some $ and a trip to the audio doctor.

 

[jdurbin1]

Sweet! Way to stick with it...

John

 

[Blue Shadow]

It 's fixed and I saved some $ and a trip to the audio doctor.

That is all that matters, you fixed a Tandberg by yourself, nice.

 

[Hobbit13]

{Bumbing an old discussion}

I worked on one of these pre-amps the last weeks. I replaced all electrolytes in the signal path with Wima MKS (the old range with 5mm pitch), this really made it sounding much more transparent. (I know Wima MKS is not perfect, but it's about the only thing you can get with 5mm pitch)

I checked all the old elcos with an ESR tester, and they were all still fine. They used decent quality components.

Alltough the sound quality improved, the problem remained: hum, quite a lot of it. In between songs I have a 50Hz hum with some rattling sounds around.

So I looked further: I grounded the cabinet (there was no connection between the PSU GND and the metal frame), I shielded the 220V wires inside. Again some improvement, but still too much hum.

I noticed that the hum increased when I pressed "tone defeat", which is opposite of the expected behavior. Thus I checked all switches. There were quite some bad solder joints on the switches, something to look for in these devices!

Powered it up again: improvement once again, but still too much hum.

Any ideas on what to check next? (I checked the power supply, and it's clean and stable.)

Thanks in advance

 

[jdurbin1]

First thing I'd have done is to check every single board ground. One of the weak parts of the 3000-series design is that they used sheet metal screws to mount the boards to the aluminum chassis sections, AND to ground them as well.

Although this doesn't always result in problems, loose or stripped screws and resulting poor board grounds is not uncommon. The preferred solution is as follows:

1) Disassemble the unit enough so that you can get a pair of visegrips on the extruded chassis members where the screws go. A slight grab of those sections with the pliers will tighten the slot up enough to allow the screws to be tightened to spec.

2) Add jumper wires from the soldered ground points next to the screws, and run them out to a separate ground screw that you add somewhere on the chassis. Even adding another screw into one of those slots somewhere it isn't also holding the board in place would be an improvement, but better still drill a hole through a section and use a bolt/lockwasher/nut for maximum reliability. Probably would star ground that point with jumpers from it out to the various boards.

Keep looking for solder problems too. They're common at the board-to-board headers, where jumper boards connect, at the switches & controls, etc.

John

 

[JohnMac]

Yes to checking the solder joints. I found a couple on mine and after re-soldering them I've used it without any issues ever since. I use it mainly for phono and it sounds very nice.

John