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Need help with my Telefunken Studio 1 'cause it's AM only...


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#1 Ken

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Posted 15 November 2014 - 04:28 PM

Bought a second Tele Studio at a discount, thinking that a parts box would be a good thing to have.  Now I'm trying to consolidate the two into one working unit.

I'm testing the top board today because after assembly I only have AM & SW, but no FM for more than a minute or so before it all turns to static.  I'm thinking it's a capacitor that's gone bad.  I cannot check most of the alignment points because I don't have any way of injecting the signal that's needed.  I made some checks around IC 101 with my oscilloscope before losing FM but I don't find anything.  I'm also checking some diodes just downstream from the antenna input without finding anything unusual yet. 

 

Anyone have any experience working on these?  I have the service manual from the sites downloads section, and I seem to be able to puzzle out enough German to follow along, but short of a recap I seem to have hit a brick wall.  It appears this manual is OK for use with the Studio 1 & the Studio 1M.

 

I have all the boards connected, but no FM going out to the next board it seems.  Any help would be greatly appreciated because that and a re-belt seems to be the only thing between me and rocking down the house.



#2 Superduper

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Posted 15 November 2014 - 10:04 PM

Wouldn't rule out a cap but in this case, a resistor is even more likely than a cap.  I suspect the issue might be with a semiconductor, try freeze spray to see if you have any luck.  You also should do VR checks to see if any anomalies.  You also should try to narrow down whether the issue is in the RF or IF stages or with the local oscillator.



#3 skippy1969

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Posted 15 November 2014 - 11:04 PM

Hey Ken,do you have a Studio or a Studio 1M?

Are both your tuners boards bad?

Or do you think its in the main board?

I have a spare tuner board,but it's for a Studio 1M. 



#4 Ken

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Posted 16 November 2014 - 06:49 AM

Hey Ken,do you have a Studio or a Studio 1M?

Are both your tuners boards bad?

Or do you think its in the main board?

I have a spare tuner board,but it's for a Studio 1M. 

Thank you very much for your kind offer, Scott.  I'll keep that in mind, although mine are Studio 1's, not 1M's.  One had had a couple switches & connecters torn off it and I am using that one for parts for this one.  I wouldn't be surprised if a 1M tuner board would work though, because the noise reduction circuitry is on the main board (High Com, metal, cro2, etc.)

Both of these radios are in nice cosmetic shape, although one has a crack in the front by the tape deck.  Both were not working correctly when I bought them for cheap from ePay.  I'm starting to test from the very beginning and haven't hooked up & tested the decks yet, although one of them needs a repair like the one Roman did years ago on his Studio (I found his pics on s2g.)

 

I've been putting these chores off for years with the first radio.  Finally found another.  :blush:

 

I can't think of a better Christmas present for myself than a blastin' Tele!  ;-)



#5 Ken

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Posted 16 November 2014 - 07:10 AM

Wouldn't rule out a cap but in this case, a resistor is even more likely than a cap.  I suspect the issue might be with a semiconductor, try freeze spray to see if you have any luck.  You also should do VR checks to see if any anomalies.  You also should try to narrow down whether the issue is in the RF or IF stages or with the local oscillator.

Thank you, Norm, I'll get some freeze spray on Monday.  So far no anomalies in voltage checks until towards the end of the circuit (after IC 201.)  I'll try some resistance readings today, although I suspect now you may be right about it being a semiconductor.  I do find that I have 2 volts input to IC 102 where there should be 2.2v, but everything I check up to there is also very slightly attenuated.  Coming out of IC 102 I barely have 3v where there should be 4.7 volts for each of the right and left channels at pin 4 & pin 5.  The closest semiconductor is T 102, which through SW 201 k comes in on pin 1 of IC 102, where I have the correct 8V.

 

Like I said, resistance checks today around IC 102.



#6 BoomboxLover48

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Posted 16 November 2014 - 07:56 AM

Ken, Post some pics also. 



#7 skippy1969

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Posted 16 November 2014 - 11:19 AM

Just let me know if you need any parts Ken. :cool:

My parts unit's amp board is bad,but there are some good stuff left if you need anything. ;-)



#8 Prime

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Posted 16 November 2014 - 03:19 PM

Hi Ken,

The AM band works, therefore IC102 works. My first guess would be to check pin 12 of IC101 for B+ when FM is selected.

Also, the tuner boards are the same for 1 and 1M. I have both. 1M has metal tape capability, thats all.
The upper scale of UK models stop at 104Mhz instead of 108.

I you can't get it going, skippy's offer would be an easy quick fix

brett

#9 Ken

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Posted 16 November 2014 - 05:15 PM

Thanks, Brett.  I have 7.8V at pin 12 of IC 101, which is slightly less than I should have, like all readings upstream from IC 102.  Just over on the other side of L610 it says I should have 8.2V from the primary of L605/606, among others.  I have 7.8V at the junction of R602 & R617.  Their over on the other side of L610.

 

If I could find L610.  No luck so far.  Time for a break. 

 

I have a headache.  :lol:



#10 oldskool69

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Posted 16 November 2014 - 05:22 PM

I have a spare studio 1 for guts.  Lemme know if you need parts.  Keep in mind, slow is better than no so if you need them I'll have to scrape time to get it out with football season in full swing. :cool:



#11 Ken

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Posted 17 November 2014 - 06:06 AM

Thanks, Freddy.  And again, thanks everyone for the offer of spare parts.  I hope that between all of us we will have enough to get just this one going.  :-D

 

I'm back on it.  :rock:  Today should be freeze spray day.



#12 skippy1969

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Posted 17 November 2014 - 10:44 AM

Yes! We must make the Studio1 whole again! :clap:  :clap:  :clap:  :clap:  :clap:



#13 Superduper

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Posted 17 November 2014 - 03:27 PM

A general and slight attenuation of voltage across the range could be the result of supply voltage variations.  In testing, most specs call for a stable supply which might mean supplying power with a bench power supply.  The point being that if B+ to an IC calls for 8.2v and you get 7.9v probably is not sufficiently significant enough to result in tuner going from working to simply static.

 

Also, note that the schematic has the circuit split into blue colored blocks.  Each block represents a stage and you should focus your efforts on the stage that is suspected problematic.  Brent told you that AM works so IC 201 is good (and probably everything else in that block).  Also note that IC 201 feeds to IC102 (stereodecoder section).  This section is the MPX demodulator and if  you are having trouble capturing stereo, this might be a place to look at but since you are having different symptoms and because AM is having no trouble passing that circuit, it's most likely OK too.  Furthermore, anything downstream like the AF block is probably a waste of your time since again, the AM audio has pass through that part of the circuit as well and has no trouble getting amplified to line levels so look no further in that part of the circuit.  Good news for you is that it would appear that you only really need to focus on the upper left block which includes the RF, local oscillator and the FM detector sections.  If you were getting really quiet output, you would look near the end of the FM portion.  However, since you are getting static, then I would personally suspect more the front end.  There looks to be 2 FET's that might be suspect. 

 

As for why I suggested freeze spray to check, since you indicated that FM works for a minute or so before turning to static, that often has to do with a component warming up and perhaps having an internal break which gradually occurs due to thermal expansion.  It might or might not be effective to find the bad component but it's easy and cheap enough to try.

 

Anyhow, maybe some of these tips makes sense to you.  If not, then just think of it as gibberish, and ignore it, lol. Thinking too much about something that doesn't make sense might only serve to confuse you.



#14 Prime

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Posted 17 November 2014 - 06:53 PM

Thanks, Freddy.  And again, thanks everyone for the offer of spare parts.  I hope that between all of us we will have enough to get just this one going.  :-D
 
I'm back on it.  :rock:  Today should be freeze spray day.


I'm curious if IC101 is working. With the antenna up and moving the dial towards known strong fm stations; does the tuning meter move at all? Its driven off pin 14. If the meter is moving around then maybe the mute function in IC101?
If no movement then maybe IC101 not getting any 10.7mhz IF on pin 18.

#15 Prime

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Posted 17 November 2014 - 07:17 PM

I need to pay attention better.
I overlooked the "working for a minute, then drift to static" detail.
Probably not mute related then.

#16 Ken

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Posted 18 November 2014 - 06:25 PM

Eureka, I have found it!

 

T101 !  :blush:   Missed it the first time 'cause it was to high and I was looking for something to low...  :bang:

 

Big thanks to everyone who chimed in with suggestions and advise, especially Norm, who as per usual is right on target.  :thankyou:  :superduper: A semiconductor it was.  I now have the proper 6V at the collector instead of 8V like I had previous to replacement, and the correct voltages at the base & emitter instead of big fat 0's.  Don't know how I missed those the first time.  :-/

 

 



#17 Prime

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Posted 18 November 2014 - 06:56 PM

Now you can rock the house down!

#18 Ken

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Posted 18 November 2014 - 07:07 PM

On to the tape deck!  :frankenstein:



#19 skippy1969

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Posted 19 November 2014 - 06:33 AM

AWESOME!!!!!!!  :clap:  :clap:  :clap:  :clap:  :clap:  :clap:



#20 Ken

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Posted 20 November 2014 - 06:25 AM

Today's update:  FRUSTRATION!

 

Always be careful when working with 30 year old, fragile equipment, because if you slip, THINGS BREAK!

 

I broke the main power switch and had to re-solder the main connections onto the opposite side of the switch.  Lucky me there WAS another side to the switch.  Now I'm back where I was a day and a half ago.

 

Onward and upward!



#21 Ken

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Posted 21 November 2014 - 06:04 PM

Re-aligned the radio bands and re-installed the main power switch yesterday.  Moving on to the deck and the main PCB, I discovered the main PCB is cracked at one corner.  Already belted the deck, so I'm jumper-ing a half dozen traces this evening.  :thumbsdown:  :annoyed: .  Another problem not mentioned by the last owner, who was obviously inside this radio.  I think his nickname was "The bigger the blob, the better the job."  :nonono:



#22 skippy1969

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Posted 21 November 2014 - 08:06 PM

DANG!!!!!  :bang:  :thumbsdown:  :nugget:



#23 Ken

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Posted 22 November 2014 - 06:42 AM

Nice avatar, Scott!  A personal favorite!  :rock:

 

Back to work.  :bang: