Tandberg TR 2080 No Sound

[TomHarrison1]

I just picked up a TR 2080 over the weekend (free), with a couple of issues. After pulling cover I found that D919 and R955 have completely burned up. R953 and R943 show signs of overheating.

I've got service manuals for 2075 and 2075Mk II/2080. 2075 Manual has better resolution and can make out component values and voltage readings on schematics.

So I've ordered replacement parts (mouser has the BY206 diode). But I have a question about R943 and R944. According to schematics, they should be 10k ohm, but with my unit, both appear to be 5.6k ohm. Can someone confirm what they should be.

Also, with these signs of shorting/overheating, what else am I likely to find has gone south?

 

[gslikker]

Probably several, or most of the, output/driver transistors in that channel. remember, a shorted transistor can put certain dc voltages on places it does not belong and take out more than would be obvious. Apart from that, the initial cause of the problem may not be the measurable defective components.
Forum member jdurbin has most experience with these.

 

[TomHarrison1]

I suspected as much. While I'm waiting for the resistors and diode to come in, I'll pull and test the output transistors.

 

[TomHarrison1]

OK, my bad. I just came across this TR 2075 MkII Circuit Diagram and Boards manual that answers some of my questions. This is the best quality scan I have found, and the values are different from the 2075 manual I was using.

http://sportsbil.com/tandberg/tr-2075mkii-s.pdf

R943 and R944 are in fact 5.6k ohm (not 10k as they are on the 2075)

D919 (CR919) should be 1N4004 (not BY206 as they are on the 2075)

I found a 1N4007 diode on PartsExpress that is 1000v equivalent to 1N4004 (300v). Is this a safe substitute?

As for the Output transistors. I don't see them on the diagrams/schematics. Can someone help with original part numbers and new equivalents for a 2080?

 

[TomHarrison1]

Also looking for equivalents to FT317A/FT417A Driver pairs. Not finding much in my searches.

Though I did find a thread on the Output pair and equivalents. OnSemis MJ15003G/MJ15004G

 

[slimecity]

Have you tested the outputs yet? Those burned resistors are probably placed in the circuit as "sacrificial" ones and they could even be fuse resistors. You need to start with testing the outputs then test all other transistors upstream from there.

 

[TomHarrison1]

First, here are the part numbers I see on each Output Transistor:

Q927: Motorola 2N5630 7840
Q929: Motorola 2N6029 602
Q928: Motorola 2N5630 7840
Q930: Motorola 2N6030 7840

Looks like 3 of the 4 are bad. I disconnected all leads from each and ran diode tests on all 4 in all combinations and got the following. Only Q928 looks good.

Left Channel:
Q927 black to base, red to collector: .001
Q927 black to base, red to emitter: .001
Q927 red to base, black to collector: .001
Q927 red to base, black to emitter: .001
Q927 black to emitter, red to collector: .001
Q927 red to emitter, black to collector: .001

Q929 black to base, red to collector: .528
Q929 black to base, red to emitter: .528
Q929 red to base, black to collector: 2.704
Q929 red to base, black to emitter: 2.704
Q929 black to emitter, red to collector: .001
Q929 red to emitter, black to collector: .001

Right Channel:
Q928 black to base, red to collector: OL
Q928 black to base, red to emitter: OL
Q928 red to base, black to collector: .467
Q928 red to base, black to emitter: .475
Q928 black to emitter, red to collector: OL
Q928 red to emitter, black to collector: OL

Q930 black to base, red to collector: .467
Q930 black to base, red to emitter: .340
Q930 red to base, black to collector: OL
Q930 red to base, black to emitter: 856
Q930 black to emitter, red to collector: .862
Q930 red to emitter, black to collector: OL

I'll check drivers next...

 

[slimecity]

Roger that. Chances are you may find that some of the pre-drivers are also gone.

 

[TomHarrison1]

So best to test all trannies down the line, order, replace bad ones before firing it back up?

Since this unit has pre ins and outs, would it be ok to plug an amp into it to test the rest of this receiver, or should I wait, given its current condition?

 

[jdurbin1]

I'd replace the 1000uF/63V cap in the +25V regulated supply first, it's probably an aging Frako like the ones I see on that power amp board. Make sure you check those too BTW, very common to find one or both has failed and is causing excess DC offset which can lead to the final stage failing. Either way I'd only test the preamp & tuner after unplugging the power supply from the Pa board.

There are multiple board versions for the power amp, and the available documentation covers only three of them: 2075 (earliest model, full service manual), 2075 MkII early (that's the Norway schematic for the MkII, which also can be used on late production 2075's), and the 2075 MkII/2080 manual which is the relevant one for your receiver (as long as someone hasn't been swapping boards!).

Those gold Frako caps tell me this is probably a relatively early production 2080, they switched brands later.

Did someone really sub a 2N6029 in place of a 2N6030? That's not good... probably not working now either.

I think I've used OnSemi equivalents for those drivers at some point, but would have to check that. Pin out may be an issue too.

John

 

[TomHarrison1]

Hi John. Was hoping I would hear from you . So I fixed a few amps, replaced caps, resistors and trannies. But I don't know parts by use. If you can steer me to what C number those 1000 uF caps are that would be grateful.

I've got the OnSemi's on order and have just pulled the 2 left channel drivers. The one next to D919 is pretty blackened. Nice fire there at the time those failed.

Still trying to track down replacement driver equivalents.

Tom​

 

[gslikker]

Two channels out, I would make sure to have a variac around and/or limit current at the transformer secondary connections through power resistors when troubleshooting. (although, on AK people seem prefer a "dbt").

Maybe MJE15032/33 or such can be considered for drivers? Just guessing here.

Now IF one of the amplifiers did have its output shorted to MINUS voltage you can also assume the right part of the input pair did have its emitter-base junction " zenering" which can have deteriorated the transistor. In that case, additionally the input pair could be suspect too.
A TR2075 I recently updated, did have " crackling problems" (sometimes very loud) which I could not trace and while some transistors reacted on cold spray I ended up replacing differential pair and the next ones also.
Differential input pair became 2*KSC1845, BF381 I did put in KSC2330 instead and the Q907/Q911 pair I put in 2N5416S which I had around.
Be aware also the limiting circuit (which I do not really comprehend without more studying) can have defective transistors as well...

 

[jdurbin1]

C610, big axial cap laying on its side on the source select/regulator board, left hand side under the tuner.

Here are some other AK links on those drivers (bridges 2075 and 2080 but the parts should be similar, as all of these models used the same Motorola output sets originally):

http://audiokarma.org/forums/index....tired-tandberg-tr-2075-recently.714997/page-2

http://audiokarma.org/forums/index.php?threads/help-needed-for-a-tandberg-tr-2075-mkii.628617/

That last one suggests I did find & order OnSemi parts for the drivers, but I've forgotten the numbers. The ones gslikker mentioned sound familiar, though.

This one cites some modern replacements a friend of mine in the Netherlands told me about. there's a mistake on part number in one of my posts but read posts 8 thru 12:

http://audiokarma.org/forums/index.php?threads/tandberg-tr2075-output-transistors-needed.267250/


John

 

[TomHarrison1]

Thanks, I'll take a look at those Frakos. I pulled the left channel drivers Q923 (NEC D608A R75) and Q925 (NEC B628A R78) and they both look bad. I haven't pulled right channel yet.

These NECs don't appear to be original according to schematics (should be FT317A/FT417A?), but the solder joints looked original. Can someone confirm what equivalents I should be looking to order.

 

[TomHarrison1]

I pulled the right channel drivers Q924 (NEC D608A R75) and Q926 (NEC B628A R78) and only Q926 looks bad. Pulled C610 Frako and it reads 1208 uF. But I'll pull the other Frakos and go ahead and replace them all as you suggest.

Still need help on replacement drivers since 3 of 4 are bad.

 

[TomHarrison1]

OK, just pulled and checked the Frakos on the Amp board.

Left channel:
C905: 0 uF (should be 470/6v)
C913: 255 uF (should be 220/63v)

Right channel:
C906: 762 uF (470/6v)
C914: 267 uF (220/63v)

 

[gslikker]

Myself if having to buy new I would try the MJE15032 and such, they are designed for this kind of circuits.......For the outputs, indeed the MJ 15001,2,3,4 MJ15024,25 MJ21194, etc, all qualify.

Just be prepared probably more is at fault...

 

[TomHarrison1]

So mouser has the MJE15032G's, but the 33's are back ordered until March. What about the TIP2955/3055 pair that John mentioned in the third link of his post #13 above. The 32/33's are rated up to 250v C-E, 250v C-B and the 2955/3055's are only 60/100v. But since the rails are +-52v, will the 2955/3055's suffice?

 

[gslikker]

No, they are not suitable at all. He stated the types "came to mind" talking to some tech in the past. Practically they will not have been used as drivers.

There are more reasons but it starts with the fact the package is bigger so they do not fit the holes in the circuit card, they take too much space.

 

[TomHarrison1]

Ah. Ok. Rats. I'll look for another source or I guess wait til March

I found one source but that have a $25 minimum order. Guess I could buy some of the other electrolytics. Already ordered replacements for the Frakos at mouser.