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Tandburg 2080 restoration problems

James Cox

James Cox

AK Subscriber
Subscriber
Well I'm back with another head scratcher! My friend brought me a tandberg 2080 to try to get restored and up and running for him. I tried to warn him that I'm more familiar with tube stuff and have only done basic recaps on solid state gear but he wouldnt listen!

So we this thing arrived on my bench it would power up but there was no sound from the speakers. After a once over I noticed that the 6v 3w festoon lamp fuse on the regulator board had blown. These are kind of expensive so I advised that we should do a basic recap (saving the more expensive filter caps for last once we get this thing making music) to avoid wasting the lamp fuses. After the recap the fuse is now staying steady dim and I'm getting noise from the speakers but the hum drowns out any music.

I found a troubleshooting thread and that lead me to check the +25v rail and I'm getting around 29v. Is that close enough? I've checked all diodes in circuit and none are reading shorted or open and when I power on with my DBT hooked up the light immediately dims to almost no light so that's a good sign! Also I found if I remove the jumpers and plug a source with volume control direct to the power amp I get clean sound from.both channels. That makes me think something wrong on the preamp board but not positive where to start digging. Oh also the replacement lamp fuses I found are a little smaller than the originals but the do fit. I blew 2 or 3 in the process of getting this thing recapped but they are finally steady.
 
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I have a marantz receiver I may try connecting the power amp from.that to the preamp.in the tandberg and see what it does. I'll report back with my findings
 
Alright so I hooked up the preamp from the tandberg to the poweramp in my marantz and the hum persists. The hum does get louder with the volume control and overpowers the music to the point that you can barely hear anything besides the hum. I'm also getting a but of electricity flowing through the shaft of the volume control and when I connected both receivers I got a light shock from the faceplate of the marantz. That makes me think the problem is a ground issue somewhere... anynideas where to start?
 
sanjib said:
I hope the Tandberg specialist @jdurbin1 will come to help you!
Click to expand...
Haha same here! Its actually his posts that gave me the courage to tackle this job in the first place. And yeah I know I can adjust the voltage but since it's fairly close wanted to track down the source of the hum first. I've ruled out the main power amp board. The shock I'm getting makes me think a ground issue but I havnt quite figured it outyet
 
Why not send him (jdurbin1) a PM about your problem on the Tandberg 2080?.......that is if you have not done so already.
 
R-2-R said:
Why not send him (jdurbin1) a PM about your problem on the Tandberg 2080?.......that is if you have not done so already.
Click to expand...
I'll do that if he doesnt fimd the thread on his own. I'm sure it's something simple I'm missing I just dont want to start removing and testing random transistors until I've determined where the problem is.
 
Is that black wire from the preamp board still floating around loose? That grounds the board... as do some of the board mounting screws. Make sure ALL of those are snug, don't overtighten to the point of stripping out the aluminum channels though.

Set the +25V per the manual. A bunch of the rest of the receiver uses that regulated supply, so having it at 29V (16% high!) isn't helping anything; in particular it will shred the FM alignment as the tuner 100% relies on that being accurate. It's also potentially exposing some downstream components to higher voltage than they should be exposed to.

Did your partial recap include the 1000uF/63V axial cap next to that current-limiter festoon lamp on the source select/regulator board? If not, do it now - they're a known weak point and that filters the +25V line so any AC ripple downstream shows up a bunch of places you don't want it.

Aside from that, check the replacement cap installation (if you did any) for the smaller caps on the preamp and filter boards.

These aren't prone to hum issues generally, so I'd suspect either poor grounding or a cap in backwards somewhere, or maybe a cracked solder joint on one of the preamp/filter boards - in particular, look at where the headers solder in for harnesses that run board to board.

Last, make sure you thoroughly deox and reseat all of the signal cable harnesses: from preamp to rear panel jacks, back to the power amp. I usually spray the male part, run that in and out of the jack a few times to wipe away any oxidation spots.

John
 
So the black wire is screwed down and all the screws are good and tight. As far as which caps have been changed, every electrolytic besides the big Siemens filter caps have been changed. I didnt mess with the FM section because I dont have the tools to realign it so I figured itd be best not to mess with the tuner sections until I at least get everything else in order. I double checked all the caps and they all appear to be in the correct orientation. As far as the cable harnesses, I havnt deoxited those yet but will get that done and report back. Maybe I accidentally swapped a wire and plugged it into the wrong spot? I'll compare with the pics I took before unhooking everything and see what it looks like. I'm about to head out and wont be in for a few days so may be Saturday before I can do any further trouble shooting. Thanks for you help!
 
Also, based on the fact that using the poweramp only I have clean sound, does it sound like my issues is in the preamp, voltage board, or mode filter board? That's the area I'm focusing my attention to now since the poweramp is working... now I will say the hum isnt a typical background hum. It overpowers everything and makes a thump noise if I press and of the selector buttons and theres a big thump when powering on or off
 
Also, even though all the controls have been heavily cleaned if I touch any of the controls while its on theres a loud static electricity type sound. I got the voltage down to 25v btw
 
Yeah it's on the front boards, your power amp test was pretty conclusive on that part. With as much drama as you're describing, swapped connectors or solder bridge somewhere would be high on the list of possibles, then broken solder joint somewhere.

If you want to post some pictures of the replacement cap installs, I can compare them to known correct original boards but the cap polarity markings will need to show in the pictures. Generally the board markings are accurate on these but I've literally never needed to recap one of these receivers to make it work correctly, so couldn't tell you 100% they don't have a marking wrong somewhere. And, if any of the parts you replaced were the old axial caps, it's easier to make a mistake orienting a radial replacement.

John
 
Awesome, that's what I was thinking too. I'm going to be busy until Saturday but I'll sit back down with it Saturday and double check all the boards and post some good pics. Hopefully I'll be able to spot an obvious issue somewhere
 
So I've only got about an hr to tinker with this thing today but I did go ahead and snag some pics. I'm going to hit all the wire harnesses with deoxit and check for loose connections on the boards while I'm here
 
Well, the caps all look correct for orientation and I don't see any marking errors on the set I checked here so that can probably be dismissed as a possible cause.

Checking the harnesses for possible swaps would mean opening a 2080 and I probably won't get to that very soon, but you can use the PCB connector markings to track which harness goes where; I think it's only the 2-pin ones that could be swapped, anyway.

Have you done the cracked solder inspection, checked for solder bridges? Those multi-pin connectors in particular should be inspected closely - more likely to find some erosion around a pin that a problem of this magnitude caused by oxidation (only place I'd really worry about that is the plugs/jacks for the coax signal cables).

What type caps did you use to replace the orange low-leakage originals? I can't tell from the pics, but if those weren't replaced with UKL-series (or equivalent), they should be. Regular caps (even if they're labeled "audio grade") aren't correct for those locations.

John
 
Cool, thanks for checking your board for me. I only had time to check the voltage regulator board today and I did find one loose connection but I dont think it's the cause of the problem. I'll have more time to dig in next week and will double check the rest of the boards and the wiring layout then. I used nichicon capacitors but I'm not positive which series. I'll have to check my order list and see.
 
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