Is this normal?

[jdurbin1]

Not unusual for those board connector jacks to develop cracked solder. Check for that around the pins on each connector, in addition to the deox work.

Binkman, the meter drive comes straight off the TDA 1047 with an adjustment pot along the way. It's normal to see the voltage that way if for some reason the IC isn't pulling one side low or high, or if there's a broken connection on either side of the meter circuit which seems to have been the case.

John

 

[P. Hageman]

Today I have cleaned all connectors on the FM board, took some close look at every solder-connection and again measured the voltage on both the IC's. Voltage's IC 1047 on pin 14 and 15 are not correct??? I also made a small film on the movement of the signal meters, so you can see. I do not have a clue anymore and feeling a bit dissapointed at this moment......................................

 

[Mr. Nick]

I can see that. Signal strength meter is almost dead.
Yesterday evening my TR2025 started acting up again. It worked very well on different days for many hours per day with no problems. On these days I kept the case open, since I waited until it would begin acting up again.
So, that never happened and I put the case screws from the bottom and top panels back on, secured screws normally. I put it back on and watch it for couple of minutes, tuner working great UNTIL.. in 30 seconds of time frame, signal strength gradually began losing signal strength until the needle is back at 0 -strength level. How funny is this?

So today I open the FM front end case (shiny metal box) and discovered few transistors had their legs in some nasty looking build up on them. Before this I tested I had zero signal strength.
At certain angle it would almost look like the legs were corroded. Well, can't be sure, since some transistors and ICs have copper finish on the legs.
Anyway scraped that build up away with a tip of a flathead screwdriver from several transistors and fired up the Tandberg again in dim bulb.
WOW, gotta say wow, now I have the signal strength at between 3 and 4 on the scale. Just 15 minutes ago I had the strength at 0 level.
Can't say, if this was the solution, time will tell, but I can't perform any tests, until it starts acting up again.

Peter, given the condition of your connectors there are probably more connectors which need cleaning.
Suggest to take a look what you find from the front end, also check the wires connected into front end box.

Take a look, this is what one of the transistors looked like before I cleaned the transistor legs.

 

[P. Hageman]

Nick, thanks thats worth looking for. BUT, how do I open the tin box??

 

[Mr. Nick]

Top part of the box lifts upwards after you have desoldered the black ground wire off from it.
Have a very good spot light to work inside the front end, because there are very thin wire threads coming out of the certain FM components.

Now I have had Tandberg on for 3 hours, signal strength sitting firmly at close to level 4 on the scale.
Before I worked the front end, it would go between 2 and 3 at best.

 

[P. Hageman]

Nick, I opend the top part of the box and sprayed with some tuner cleaner, left it for a few minutes and then dryed it with air. No such nasty looking build up anywhere as far as I can see. What I also find strange is when I push the "Mute" button, no sound at all, even when I am tuned in at a loud station, thats not how the mute should work I think, or is it? I think this is going above the level of what I can do anymore. Think I reach the point of decide what to do with it. I am not used to quit on a project, but this is getting to frustrate me, every time hoping for a solution but no succes sofar. I still think the reason must be something small, but..........................Its a pity I already invested in all those replacement parts.

 

[Mr. Nick]

This is a true challenge for you. You have done well so far, shown ability to change components correctly, measure voltages from locations and managed to bring center tuning meter into life.
Don't give up now, I know it looks like big obstacle and it's frustrating to perform actions to find out efforts were in vain. You will get to the bottom of this!

There are in fact many things you can do.
For example you can put the receiver standing sideways and ensure from both ICs (1047 & 1310) with your multimeter that each pin has a good contact to the solder side of the IC socket, did you do this yet?
Also that you had a wrong component fitted at incorrect location - have you checked the FM decoder board carefully, if there are any other incorrectly fitted components like "C233" ?
It might be something very simple in the end that is messing up the circuit. Also you could measure the voltages from each of both uA703 IC pins and compare them to the schematic's voltages.
Check that you have about 23,5V entering via resistor R254 to the FM front end, is it present?

The muting function should mute the weak signal reception and as your signal strength is weak, it's muting the entire FM band. The muting function is probably alright. Problem lies elsewhere.

What John has to say about Tandberg front ends, have there been any problems in the past?

 

[P. Hageman]

Nick, thanks. I won't be able to work on this machine for a few days. Hope to be back home on saturday. In the mean time, keep them coming all those suggestions on how this could be fixed Perhaps John will tune in as well.

 

[Binkman]

Perhaps.getting away for awhile is a good thing.

when I push the "Mute" button, no sound at all, even when I am tuned in at a loud station, thats not how the mute should work I think, or is it?

Normal. i.e. if you had an outdoor ant. on a rotor and able to tune in stations far away, local stations can be dropped with the mute allowing finer tuning.
--------------------

Binkman, the meter drive comes straight off the TDA 1047 with an adjustment pot along the way. It's normal to see the voltage that way if for some reason the IC isn't pulling one side low or high, or if there's a broken connection on either side of the meter circuit which seems to have been the case.

So.. where can OP apply probes to test v+/- on a strong station and a dead spot on the dial?

 

[P. Hageman]

Got home today and figured out there was just one thing that I could do with my limited knowledge. I started to resolder many contacts underside of the FM board. When I turned on the machine the signal strenght meter started moving to the right!!! I then tuned in on the strongest station and adjusted the needle with the potmeter at 4 and now it works fantastic. Even the mute button works, when scrolling over the scale no sound untill it hits the next station Think I did it, but still the stereo led is not working although the signal is strong enough. So tomorow I will look if there is also a bad solder joint. Feeling a bit proud!

 

[Binkman]

@P. Hageman Hey that's great! That time out may have paid off!
Aged solder joints... very common. these vintage puppies ain't getting any younger. led might be burned out if no joy after re-touching up those solder joints.

 

[P. Hageman]

I have done all the soldering and connectors, but the stereo led won't light up due to the fact that the voltage difference is to low (11,6V -13,13V). I then checked the voltage on C229, one side 13,75V (must be 15V) against 0,0V the other side , voltage on C228 one side 13,13V (must be 14V) against 0,0V the other side. So the voltage's seem to be a bit low. I was thinking perhaps Q202 could be faulty? I then checked the voltage on Q202, one pin 13,1V (must be 14V), second pin 20,5V (must be 19V) middle pin 13,7V (must be 15V) I thought to replace this transistor (MPSU 06), would that be a good suggestion, as it looks as if the voltagedrop starts there. Advise would be much appriciated!

 

[Binkman]

Worth a try. I did post a diagram asking where to test on strong locked signal where I assume the led is lit and then a dead spot on the dial both meter and react. If in fact it is an led or a wheat bulb?
pretty long day and didn't refer to the sm.

 

[jdurbin1]

The stereo indicator is an LED, unless someone has replaced it incorrectly.

Peter, can you hear stereo separation when you are on a strong station? Using headphones it should be pretty obvious whether it’s pulling stereo or stays in mono.

You could still be lower in signal strength than needed to reach the stereo threshold - and that threshold could also be set too high. If you are hearing stereo though, unplug the LED and reverse it and see if it doesn’t light up. Or use your meter to test it, every once in awhile these do die but I’ve found more that were just plugged in backwards.

John

 

[Binkman]

I know you adjusted he meter strength and unless you also adjusted R215 (led) you can try (note counter clockwise (+) clocik-wise 0) If never adj. then led probably out.

 

[P. Hageman]

John, I know the indicator is a led, its connected in the right way. I also checked if the led was working. It did light on 3Volt. As you advised I used my headphones but no stereo sound. Talking about the stereo threshold, is there a way to lower that threshold? Today I removed the front end box and cleaned underneath the board and resoldered every contact, I also got the MPSU 06 (Q202) and replaced the old one. Still no stereo. I am starting to think the reason for not getting a stereo signal could have to do with badly alignement of the FM??? Could bad FM alignement result in not getting stereo? By the way I made a small film where you can see how the meters react on FM signal.You can also hear the muting is working fine now I think.

 

[Binkman]

I'd rather watch 'Sydney Toler' in ciry of darkness... however appears meters working properly on signal strength. . Tuner meter stays in center with little fluctuation if normal.?? muting is working.

Did you try adjusting VR 215 till it lights up?? .. above post #55 and in the ser. man. (mono button off?)

 

[birchoak]

I believe that this is pretty normal as I have several amplifiers that do this when you touch the exposed metal can at the top. These capacitors are in the signal chain so what's happening is an effect like when you touch the end of a guitar jack plugged into a guitar amplifier. Same thing happens when you touch any of the RCA inputs of your stereo.

Ditto.

 

[P. Hageman]

It is working again like it should! With the help of a friend we suddely noticed the oscillator frequency was way out of the 19KHz. So after adjusting that to exactly 19KHz and readjusting R215, the stereo light started working and at last also the stereo signal was there. So after all this work, it payed of, I now have a perfectly working TR2025 with an amazing crisp sound Thank you all for helping me out with this matter, so nice! Peter

 

[jdurbin1]

Good catch on that. Can almost guarantee someone before you was busy inside twisting and turning pots and other adjustments.

At this point, if you have access to non-ferrous tools to do the adjustments, I would optimize the front end. I bet there is a lot more sensitivity to be had there but you need those plastic or ceramic tools to do it.

John