Tandberg TR 2045 Phono Stage Noise

[Westlind]

Having been bitten by the Tandberg bug (by a TR 2030 I picked up a couple months ago), I recently acquired a neglected but mostly whole TR 2045. When I got it it was covered in dust and grime and produced only crackle, but several hours of tedious cleaning and Deoxing resulted in great FM reception and almost everything working just fine. I replaced the burnt-out lamps with some obtained from jdurbin (thanks John!), cleaned the filth from the face and buttons, etc. It's a good looking unit!

But here's the issue: when I push the "Phono" button, the unit produces a horrible racket - a low, throaty roar akin to a motorcycle revving. It seems to escalate in tone until the unit gets warm, then maintains a steady racket. And it's LOUD. (Notably, if I turn on one of the Tape circuits and turn the volume all the way up, I can hear the same tone, though faintly).

I've checked all the circuitry in the phono stage for shorts, and can't find anything. Everything seems to be connected to the circuit board the way it should be, I'm getting continuity everywhere where I should get continuity, and not where I shouldn't, and am kind of at a loss. Phono stage capacitors are all capaciting. Any ideas for what I should be looking for?

Thanks in advance!
Dennis

 

[rcs16]

I found a schematic at hifiengine for TR2045. Does it do it on both phono channels?
Sounds like motorboating, low freq oscillations.
I do not know what you mean "Phono stage capacitors are all capaciting" did you actually measure them?
There is not too much in there, two stage gain using BC549B bjts, try changing all the ecaps in the phono section.
these are all common parts. Use Nichicon UKL(UES,Muse BP) for coupling and UPW or Panasonic FM (low esr) for C509,510. Match capacity and voltages

Good luck
Rick

 

[Westlind]

Hi Rick! Motorboating is a good description - oscillations in both channels.

Regarding capacitors, I was just trying to be clever - they're working and I measured them. Changed them out for Nichicons, same result.

I found that schematic as well, and everything seems to be present and wired up correctly.

Thanks!

 

[jdurbin1]

Two things I would suggest:

1) If you haven't already done it, replace the 1000uF/63V cap that filters the +25V regulated supply. That cap can cause a ton of noise downstream if it's starting to go... including in the RIAA circuits.

2) Look for bad transistors in the phono circuit, I've seen them fail in odd ways esp. when they're being exposed to a lot of AC ripple from the aforementioned cap failure. Might try some cold spray and see if you can isolate a particular transistor, but they're not difficult to just replace, either - Mouser will have the current "BC" equivalent to whatever the originals are.

John

 

[Westlind]

Thanks John - I really appreciate the suggestions. I have replaced the 1000uF Frako and adjusted the +25V supply. My next guess was to look at transistors, so that will be my next step. I'm headed off for Spring Break, so it might be a couple weeks until I get back and order them from Mouser (already found what I need), and then I'll post an update.

I do have a bit more info on the racket it makes: when the unit is relatively cold, it makes a horrendous roar out of both channels; the warmer it gets, the more the roar shifts to the left channel and becomes more intermittent in the right. It's not some slight phono channel hiss or hum; it's louder than a full in-tune FM signal at the same volume setting.

 

[jdurbin1]

Means there's pretty significant gain after the noise source which would to me again suggest the transistors in the phono circuit as the likely source.

John

 

[Westlind]

Well, now I'm stumped. Got back from vacation, ordered transistors, and replaced them all in the phono circuit. I managed to change the character of the noise, but not eliminate it. Here's what I now get: upon power-up, there is a very loud, low (estimating about 1000hz) steady hum out of both channels for about 7-10 seconds; that then gradually subsides and goes away in a few seconds; what continues is an intermittent crackling noise out of both channels, not unlike the sound of wind over a microphone, that does not go away. I've sprayed every component in the phono circuit with cold compressed air trying to find if I can locate a noisy transistor, but nothing I do seems to affect the sound. I hooked up a turntable just to see what happens; the phono signal comes through and is appropriately amplified, but the crackle persists (and overwhelms the incoming phono signals).

The tuner and the two tape inputs work perfectly; in the worst case, I could always hook up a phono preamp to one of the tape inputs, but given that Tandberg phono stages tend to be great, I hate to do that. Any thoughts or suggestions?

Thanks!
D

 

[bimasta]

I'm just observing this exchange with interest, as all my main system is Tandberg (separates). I'm constantly impressed by John's knowledge and willingness to help — the intended purpose of AK personified. And I wish you the best results Dennis — T'berg is so good — and so underrated.

 

[jdurbin1]

Do you have a scope? Would be interested in looking at whether there's noise that tracks with what your hearing on the +25V line into that circuit, which you can check at the common connection between R5521/R522. That line is filtered by C509/C510, a pair of 100uF caps - might look at replacing those. Also I'd be checking to make sure the grounding is ok. Tandberg tended to use screws through metal clips to ground boards, those can oxidize or work loose over time.

Do you get any of this noise when you power it up with another input selected, like FM or one of the tape inputs?

John

 

[Westlind]

Thanks John - Sadly, I don't have a scope (something to put on my wish list). For what it's worth, I did check the +25V line with a voltmeter, and it is providing exactly 25.0 volts. Also checked the R521/R522 connection (it was fine), I'd already replaced the C509/C510 caps, and grounding is good. I don't get any of that noise when another input is selected - FM and both tape inputs are working great. Just for kicks, I plugged a sound source into the phono connection after the initial loud hum died down, and it sounded OK but I'm only getting sound through the right channel. I checked continuity on all of the connections on the phono circuit (it was fine), and cleaned the solder side well with alcohol to make sure there was no carbon deposits causing arcing - but that didn't help either. I'll keep probing and checking components, but I remain stumped.

And Bimasta - thanks for the good wishes, and amen to your comments. I'm a total noob at repairing vintage audio, but I'm really enjoying the learning process. John and others at AK are the best - I just hope that someday I'll be able to contribute a few solutions in addition to my problems!

Dennis

 

[Westlind]

Another quick update, after tinkering and checking connections this weekend: the loud phono stage noise on startup is gone - hurray! I wish I knew what it was and what I did to make it stop, but it's gone. But, the phono circuit has a new mystery - I still only get sound out of the right channel. I think the left channel is working, since if I poke a bare wire into the left channel point on the DIN input, I get a nice healthy crackle noise. The same cable and input source works fine on both Tape inputs, so I have some troubleshooting to do, I just ran out of time. I'll try a different cable and input source tonight and provide an update. Still, I consider this progress!

 

[jdurbin1]

It could be progress, if it stays gone. I'd look really closely at the soldering work on that part of the board, esp. the newly replaced parts, and as mentioned any board grounds in the area. Open ground is a very common cause for this kind of thing in general (not specific to Tandberg). There isn't anywhere near enough voltage/signal on that board for carbon arcing, and it would take a long time for a cap to leak enough to saturate the board and create a short and by then it would be very visible.

It wasn't DC I would be looking for on the +25V line (or where those two resistors are common, which is the +25V line) but excess AC noise. Moot point though; if that was the root cause it wouldn't have disappeared like it has. You're chasing either connection issues (solder or board ground or possibly flaky connections at the DIN plug/jack), or possibly an intermittent component and you've already done the legwork to look for that one.

If you're getting noise on the dead channel at the DIN jack with a wire stuck in there, sounds like the DIN plug/adapter is either N/G or not wired correctly for that jack. There are diagrams for those connectors on the last page of most Tandberg receiver owner's manuals as well as in the schematic.

John

 

[Westlind]

Thanks again, John - so far, it's staying gone. I went through all of the soldering work last night, and it seems solid - continuity where there should be, not where there shouldn't be. Plugged in a turntable, and got good sound out of both channels. I assumed the wiring for a tape input was the same for the phono input, but perhaps I'm mistaken - the cable I used worked just fine to connect my ipod to the tape inputs, but only produced sound out of one channel on the phono input (i turned the ipod volume way, way down when plugged into the phono input). I'm keeping my fingers crossed that it's fixed, although I would feel a lot better identifying an actual flaw and repairing it than having some divine intervention solving the problem. I'll give it another good going-through before reassembly. Then, assuming it stays fixed, I'll have two fully operational and aesthetically pleasings Tandbergs - the 2045 and a 2030. I need to decide which one to keep for myself and which one to give to my son (who wouldn't use the phono input anyway, at least not now). I picked up a non-operational 2025 at the Goodwill, which is my next project. And then I really need to go into some sort of rehab program - this stuff is too addictive, and I fear the day I find a 2080 at a decent price...

Thanks again for the help!
D

 

[Westlind]

Just when I thought it was safe... the noise is back.

Here's what's happening: I thought it had gone, since while I was troubleshooting it, it went away. I left it for a few hours, came back, no noise. I left it overnight, came back the next morning, no noise. But then I left it for a couple of days when I was out of town; turned it on, and the noise was back.

I'm clearly no expert, but I have a theory: could it be that when a capacitor builds up a charge, there is no problem, but when the capacitor is left for days with no current coming in, that triggers the noise? I can't think of anything else that would cause a problem only when the unit has been sitting for a significant period of time. Thoughts greatly appreciated!
Dennis

 

[jdurbin1]

Mmm, doubt it... but, stranger things have happened.

On the plus side, the 2030 is pretty much identical to the 2045 other than the power ratings (and related transistors & voltages in the amp) so what you've learned from that one will be very relevant when you work on the 2030.

John

 

[Westlind]

Very true - I've learned a ton on this 2045. Aside from that temporary noise, it's a beautiful receiver and sounds great. And, given that it was close to dead when I came by it, I still feel I contributed to extending its useful life. It may end up going to my son - he won't use the phono stage, and has an appreciation for fine vintage things. Thanks again!

 

[slimecity]

What about grounding? That may not entirely explain why you lost sound in one channel but could explain the noise. Is grounding OK on the phono inputs and is the phono section on a separate board to the rest of the amp, how is it connected to the chassis? Are there any loose screws that could affect grounding? What about any cable connectors, any loose connectors?

 

[Westlind]

Hi Slimecity - and thanks for the thoughts. I checked, and I think the grounding is OK; from what I can tell, the board screws on to the chassis, and there are two connection points that contact the chassis right next to that screw - I made sure they make good contact, tightened the screw and tested for continuity, and it seems to be getting good ground. I tried all the cable connectors, and gave them all a spray of Deoxit Gold and took them on and off several times before returning them; it might be worth giving them all another check, but I'm not sure it would explain why the noise goes away after 10-15 seconds (and why it only occurs when the unit has been sitting for a while). The noise has a very regular decay curve - not intermittent like I'd expect with a short or a faulty connection.

 

[c_dk]

It sure sounds like cold solder joint. Places to look first: joints with a larger thermal mass like Molex pin connectors. Tougher to get hot enough during manufacture they will crack over time and cause all kinds of intermittants. With the plastic end of a screw driver you can carefully manipulate the board while you monitor your signal at a low, low volume level to see if you can make/ break the signal.

 

[Westlind]

Not a bad idea - I'm relatively happy and confident with the solder joints I've made, but there are quite a few in the phono section that I didn't touch. I'll give it a look this weekend. Thanks!