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Old 8th Oct 2018, 8:23 pm   #1
NorfolkDaveUK
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Default Tandberg 3000x annoying problem

I`m still trying to figure out this darn thing . I will try and describe where I`m at the best I can but its a bit weird . Soo ...

This machine has been a pain since I bought it . First the belts were gone so I did those then there was something wrong with the brakes so I sorted that and that was the extent of the mechanicals , then I moved on to the electrical . So it plays really well , in stereo and sounds great , input how ever is really messed up . The 5 pin din plug was fubar`d so I changed that and now I get a signal on input , BUT , its got a messed up signal . It`s as if the 2 channels are crossed over somewhere and I`m getting left and right signals combines going through the input amp , I`ve looked and looked and I can`t see any physical shorts , I`ve replaced all of the transistors , replaces all of the capacitors and still the darn thing doesn't want to play ball . When I try and scope the signal , I get what looks to be both signals totally out of phase with each other on the same trace if you understand that i mean . So i get a signal that looks like the one I`ve drawn in the pic (when inputting a sine wave). Any ideas before I designate this to the spares bin I`m getting fed up with it now ? Would be a shame its in the original boxes and everything . I`ve checked the socket I put in for shorts and there doesn`t seem to be any but I think I`m going to take it off and look properly . it really can`t be much else .

Ta !
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Old 8th Oct 2018, 10:51 pm   #2
Andrew64
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Default Re: Tandberg 3000x annoying problem

Hi Dave,
Looking at your drawing of the trace I think your horizontal sweep is to slow so the scope is not showing a true representation of the input, try speeding up the sweep speed and you may need to play with the sync as well, you should get a sinewave then. As for the messed up input it does sound (sorry) like there is a short between the channels somewhere.
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Old 8th Oct 2018, 11:03 pm   #3
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Default Re: Tandberg 3000x annoying problem

Hi Andrew , Thanks for your reply , no it`s not the scope bud , the scope has an auto set function so its automatic , you press the button and it sets everything for the best looking trace , in every other machine / circuit it displays the sine wave just fine . I will check it out but pretty sure its not the scope (fluke 100mhz 4 channel PM3082) . I will try a different probe , but when I test the signal coming out of the function generator its fine . As for the short I`m still looking but I`m damned if I can find one . Its about to hit the scrap bin soon ..lol .
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Old 9th Oct 2018, 12:15 am   #4
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Default Re: Tandberg 3000x annoying problem

Right now, I suggest you leave it severely alone and come back to it in a few days or weeks. It is either something very subtle or blindingly obvious, and at this point you are too close to see which it is. Decent 3000s aren't that thick on the ground that you can bin one just because it won't co-operate.
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Old 9th Oct 2018, 12:44 am   #5
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Default Re: Tandberg 3000x annoying problem

hehe , yeah I`m just venting when I say that Ken dont worry I wont scrap it , its in mint condition and like I say has all the original boxes , even has the plastic lid that comes with it and THAT has its own original box too and what did I pay ? 23 inc shipping ..lol . I think its more a power issue than it is anything else , someone (not me ) has re-wired the transformer , and I just noticed that the fuse on there was blown but everything was still working (hence i didnt notice the blown fuse ) so something is definitely amiss there . I need to get that sorted before anything else .

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Old 9th Oct 2018, 8:02 am   #6
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Default Re: Tandberg 3000x annoying problem

If it and even its plastic cover have survived the baptism of fire which is shipping, it's a natural survivor and deserves some effort.

Put it on one side and give it a break, as Ted suggests.

When you come back to it, stuff a signal into only one channel. nothing into the other, then go probing along the channel that should be quiet. Go slow, go steady, go methodical and you'll get there.

My style of fault-finding is to test and measure the living daylights out of the set until I'm sure which component is duff, and then replace just it.

Your style seems to be to work your way through by changing likely candidates.

Both methods work, but each has drawbacks. Mine is tediously slow, too slow for a commercial repairer. Occasionally I can't decide between multiple parts and have to change the bunch anyway. The keep changing things approach can be much faster but it runs into trouble if spares aren't easily available, and it doesn't always show you how the fault occurred and it can get stuck when one part can take out another.

Whatever someone's style, it's helpful to be able to switch to the other when a job needs it.

David
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Old 9th Oct 2018, 10:14 am   #7
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Default Re: Tandberg 3000x annoying problem

capacitors i always change out for panasonics , especially if , like on this unit , it has frakkos in it , they are always dry and more often than no leaking dc , transistors I`m a bit less like that , but once i test if i test one on the bench (because you cant really accurately test them in circuit) I put a new one in its place because its a lot easier them fiddling around putting a clipped one in . this deck is awkward as heck to trace a signal on , the problem im having tracing the signal is , i get that weird trace on both channels even with the signal only going in one side .....well.....i did until last night ....once i noticed the fuse was blown and replace it the signal was better , but its still not doing what it should . When you listen to the signal from the output , it`s all coming from one speaker , BOTH input level pots adjust the input in said same speaker , and if you turn the input up too far on either pot , it squeals and clips my amp out . I`m also getting some sort of signal off the chassis , so some where its shorted to the chassis . I`m going to sort the transformer out this morning and then I`ll start over looking for the fault . The transformer is a mess on this thing . I`m going to pull the main board out again today . I had it out some weeks back to change all the capacitors so I may have caused the short putting it back in . I dont think so but its worth checking . If I dont get it solved today then it`ll go on hold anyway because I have 2 more being delivered that need to get sorted , an A77 and a Philips 4510

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Old 9th Oct 2018, 2:34 pm   #8
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Default Re: Tandberg 3000x annoying problem

" I`m also getting some sort of signal off the chassis "

Your fault description suggests a missing chassis connection.

On the original DIN socket was there a wire link across from pin 2 to the case tag of the socket?

Which exact model do you have?
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Old 9th Oct 2018, 4:23 pm   #9
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Default Re: Tandberg 3000x annoying problem

Its a 3041x bud . No there was no wire linking to the chassis from the din socket , the grounding is done via the bracket that hold the input connector board to the chassis as far as i can tell.
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Old 9th Oct 2018, 7:08 pm   #10
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Default Re: Tandberg 3000x annoying problem

OK, the manuals that I downloaded show a radio and a phono DIN external to a circuit board and the two MIC sockets on the board. Which did you change and which are you injecting the signal to?

I would proceed by checking the resistance of chassis to the earth pin of each connector then connector to connector. They should be dead short so anything more than a couple of ohms would be suspicious.

The radio, phono and mic signals are mixed by a resistor network to a common amplifier so a short between left and right at either the phono or radio sockets, but not the mic as these are independent L-R.

Using a scope and the signal injector I use a BNC T bar and connect the signal generator to CH2 on the scope and sync to that input then using CH1 to compare left to right you have a stable reference rather than syncing to whatever is on CH1 as you probe around.

Start by comparing the signals at terminals 103 and 203 on the board. If they are not easy to access then at the input level controls or the record level presets R112 and R212 and we'll take it from there.
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Old 9th Oct 2018, 7:51 pm   #11
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Default Re: Tandberg 3000x annoying problem

I had another look at the circuit and thought of another test.

Set both record switches to down and the S.O.S to normal Inject to pin 1 of the radio socket and increase both record levels to the point where the left meter shows 0DB. The right meter should be about minimum. Look at pins 3 then 5 of the radio socket. Next inject to 4. The right meter should now show 0DB and the left minimum, again compare the signals at pins 3 and 5.

Incidentally, I have a 3300 under the desk which apart from the tone controls and power amplifiers is the same machine.
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Old 9th Oct 2018, 9:42 pm   #12
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Default Re: Tandberg 3000x annoying problem

Thanks for that I`ll have a go at that in a few . Thank you . I also have a 3341 . Thats in bits , I bought it that way for spare parts only . I`m using the line in sockets for the input . I will switch to the DIN and see what that gives me and will report back later . Again . Many thanks for your input .
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Old 9th Oct 2018, 11:02 pm   #13
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Default Re: Tandberg 3000x annoying problem

OK ...we have progress . I used the DIN socket for the input , chased the signal though the input board (which I`ve done a million times already) but i noticed this time that the trace I was getting had become intermittent if I shook the board a little bit (it wasnt like that before ) . So i started giggling wires (again which i`ve done on many occasions) on the input board and sure enough one if the wires on there would clean the signal up if I giggled it enough . SO , i took that board out , cleaned up all the wiring and put it back in and low and behold , I get seperated signals at last . This is frustrating because I`ve done that once already ....anyway .,... So , thats cured the input side of things , no the only issue I have left to solve is when I turn the input up , via the input levels on the front of the deck , it gets to a certain point and then jumps to oblivion , (on both sides ) . So its goes up gradually , and then it gets to about mmmm ...1 oclock on the dial and whallop its pegs out . Does this both sides (SEPERATELY).

Just so you dont all think i`m going any more nuts than I am already I added a pic of the trace I was getting when probing the input ...
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Old 9th Oct 2018, 11:50 pm   #14
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Default Re: Tandberg 3000x annoying problem

Looks like a classic mis-triggering waveform. If you have the trigger threshold set at a level in the waveform where there is a glitch in the signal your scope can be fooled to triggering in either of two places either on rising or falling edges, giving two overlaid traces.

Have a fiddle with the trigger level control or the trigger holdoff control. Take things off of automatic if it has such a function and see if the picture resolves the ambiguity.

David
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Old 10th Oct 2018, 12:59 am   #15
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Default Re: Tandberg 3000x annoying problem

Cheers David , no it wasnt the scope it was definitely the player . Thats now resolved and the trace is now back to normal . It was one of the wires on the input board causing it , I took all the wires off , trimmed them and put them back, and now the trace is all back to normal and I have separated left and right signals again Althought you are probably right about it looking like that on the scope . it was actually good because thats how I found the fault ..lol

The problem I have now is the problem with the input levels jumping up .

Cheers
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Old 10th Oct 2018, 7:59 am   #16
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Default Re: Tandberg 3000x annoying problem

The picture on the scope has to be misleading. It could be a waveform switching fast between two sine signals shown at a timebase speed where the switching isn't resolved. Unlikely to be created in a simple analogue tape recorder. Or it may be mis-triggering showing overlaid pictures by alternating between two trigger points - the scope failing to discriminate between rising and falling crossings of the trigger point. Most commonly this is caused by a glitch on a waveform or high frequency oscillation.

What it isn't is the scope simply showing that there are two signals exactly as there appear to be on one point at the same time. That would require one point to be at two different voltages at the same time. The scope display appears to show this, but if this is true, something has gone wrong with space/time/causality. As a new Dr Who series has just started, you must expect to be attacked by a guy in a rubber monster suit at any moment.

When you see a scope picture like that, if you don't have two separate traces switched on and overlaid on the screen, it's a big clue that there is something more to find by playing with scope settings. These are exactly the circumstances where the automatic setting algorithms now found on a lot of scopes get it wrong.

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Old 10th Oct 2018, 10:24 am   #17
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Default Re: Tandberg 3000x annoying problem

Sorry, but I have to agree with David, the only way you could achieve a display like that on a single trace would be if the timebase was syncing on both positive and negative excursions and very close to the zero crossing point so that you are in fact seeing two traces one after the other.

Now, "The problem I have now is the problem with the input levels jumping up"

Is this indicated on the meter and is it going over scale or back to zero?

Try scoping at the preset resistors R112 and R212 as you increase the levels.

Interestingly the two circuits I have show different values for the front panel record level pots, either 1meg with one end not connected or 25K with all three connections used.

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Old 10th Oct 2018, 10:33 am   #18
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Default Re: Tandberg 3000x annoying problem

Thanks David. I`m very new to this scope so all the above is highly likely , except maybe the rubber monster suit , I think that`s a bit of a stretch ..hehe . Anyway , like I say I found the fault by watching that trace, moving the board about and watching the trace clean up to a normal wave so , in the end it was handy .

Does anyone have any idea why the input signal would suddenly jump up at a certain point ? Does it have anything to do with the buffer amp switching in maybe ? I`m going to see if it does the same thing using the DIN input . Even with nothing inputting , if you put it onto source and use the input levels , you can hear the point where something is kicking in and sending the needles to the peg when you have a signal inputting , the needles dont peg with nothing inputting you just get a ton of hiss.

Sorry see mos , we were typing at the same time . I`ll give those resistors a look . these are 10k pots ...lol
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Old 10th Oct 2018, 10:57 am   #19
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Default Re: Tandberg 3000x annoying problem

OK, it sounds as if it is going unstable and oscillating.

Turn the output level controls right down then scoping R112 and R212 then R106, R206 should show which stage is oscillating.

The common decoupling capacitor is C104 for the first stage and C300 on the power supply for the second but more likely is another bad connection at a cable screen or earth point.

Edit, just noticed that your circuit is completely different to the ones that I have. Can you scan the whole circuit and add it as a PDF?
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Old 10th Oct 2018, 11:10 am   #20
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Default Re: Tandberg 3000x annoying problem

Cancel all references to components. My number dyslexia has kicked in and I have been looking at the 3400 series instead of 3041
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