TF 2016 Sig Gen Help needed

[kernowcam]

Can someone advise please. The power board has a big 3055 transistor. It has 37v on collector and 7v on base fed from a new bfy51. Nothing on the emmiter 0v. Any ideas if you have access to the circuit.

Edit. Some posts were from a misnamed duplicate thread, hence the strange ordering.

[WME_bill]

TF2016
It would be helpful if you would clarify which model. TF2016 Sig Gen, or TF2106, which I cannot trace. Perhaps you could get the moderators to correct the heading, if that is what is needed.
On the assumption that you mean the TF2016 Sig Gen, which does indeed have a 2N3055, I attach the page from the manual which contains the circuit diagram of the Power Supply Unit. The rest of the circuits and the manual are too large to post on the Forum.
The emitter of the 2N3055 goes off to form the negative rail, so it goes everywhere.
wme_bill m0wpn

[tri-comp]

Originally Posted by kernowcam

Can someone advise please. The power board has a big 3055 transistor. It has 37v on collector and 7v on base fed from a new bfy51. Nothing on the emmiter 0v. Any ideas if you have access to the circuit.

You can be sure of one thing; the 2N3055 is gone.
With a forward voltage-drop of 7V across the Base-Emitter diode it's not surviving.
A dead 2N3055 could also have put a serious strain on the BFY51 and it should be checked, too.
rgds,

/tri-comp

[kernowcam]

Yes it is the 2016 unit. Thankyou for circuit.
Sorry I am dyslexic and get things like this mixed up.
I will swap the 2n3055 if you think its bad, Dad who was trying to fix this did swap it over but it may have been ruined by bfy51.

[kernowcam]

My TF 2016 is poorly.
I have managed to get the power board running with 21 and 20v output now.

There is no output at the RF socket but the counter out has a good signal with carrier, the carrier switches on and off, the machine tunes through all bands.
The deviation seems to work - all monitored off the counter output.

Attenuators coarse and fine - nothing.

I do have the manual now but not really enough skills.

[Skywave]

To investigate the workings of an item such as this, either of the following items of test gear are essential: an oscilloscope or a VTVM. Each needs to have an adequate bandwidth for the signals you need to examine.

Al. / Skywave / Oct. 3, '13 //

[dave cox]

Sadly, I don't see a (free) downloadable manual. My guess is that since the counter O/P is alive but the RF O/P isn't it's likely in the final amplifier or attenuator. At that low-ish bandwidth it should be nothing too exotic

dc

[AC/HL]

There's a hint about relays in this American Forum thread

http://www.antiqueradios.com/forums/...p?f=8&t=166945

[Radio Wrangler]

One of the biggest causes of fatality of sig gens is someone keying up a transmitter into their output. Depending on the power it can ruin attenuators and the generator's output amp (usually seperate to counter outputs)

David

[kernowcam]

I have an oscilloscope, meters etc. I have looked at the schematic and in my woolly fashion worked out the final area / attenuators would be suspect. I have checked the post attenuator relay cut out box and this does not have a signal coming into it. Tried to get at the attenuator input but not found correct point yet.

[kernowcam]

Gradually taking it apart.
Found the signal split point - to counter and amp sections. Also found the area where the signal appears to die.
Just need to remove the board as it's solder side up and I need to see other side.

[tri-comp]

Originally Posted by dave cox

Sadly, I don't see a (free) downloadable manual.

If TF 2016A is similar try this:
http://72.29.85.210/~radioama/instru...0Operating.pdf

rgds,

/tri-comp

[kernowcam]

I have made some progress.
The point where the signal dies has a 100mh choke which has overheated. Someone suggested checking the caps adjacent to this and a resistor. I am fairly confident that this is the problem - Well it is A problem, hopefully no more but he did warn that these tant caps etc do tend to fail on equipment of this age.

[dave cox]

Tant cap failed and melted a choke ! How many times have I seen that in tektronix gear ? You can either replace with a very good quality electrolytic (low ESR at HF) or risk another tant with at least 3 times any voltage it could possibly see. There look to be plenty more tants that don't have any current limiting other than a tiny choke. I would tend to replace these as well if they are in the same situation / of the same type & voltage ...

dc

[kernowcam]

I have checked the choke - failed, the tant - I managed to pull the wire out on removal as the solder was being difficult to remove, highly suspect either was as per your comments. Also changed an adjacent electrolytic and bingo - that stage is now working to TP2. Unfortunately TP3 has no signal now so 2 steps forward, 1 back but pleased with my efforts as I do have a signal on the output now albeit low.

[Radio Wrangler]

What I heard was that the price of tantalum dust had gone through the roof, and manufacturers were looking for any way to economise. They knew users derated for voltage stress, so they started making parts <ahem> less generously rated shall we say.

Failure rates went up, well organised users spotted this and started recommending their designers use even greater derating factors... and when they finally twigged, stopped using certain makes.

Rather like the issue with secret formulae for aluminium electrolytics, these little things are just ticking away waiting to fail.

David

[AC/HL]

Some posts were from a misnamed duplicate thread, hence the strange ordering.

[kernowcam]

More progress. I am looking for a signal at TP3 on RF amp board a3. Tr 4 and 6 seem to have the correct voltages, however pin 5 should have 6v which is the ALC control voltage. Its 2.5v.
I have been told as its a feedback loop may be tricky to fault find. The 2.5 v feeds to 2 FET's which then feed tr4/6. One has a 6.5v source feed from tr4 giving 3.5 at the drain, the other 6.5 from tr 6 giving 6.5 at drain. I am thinking the FET is short circuit and or the tant capacitor from drain to earth may have failed.

[orbanp1]

Originally Posted by dave cox

Sadly, I don't see a (free) downloadable manual.
...
dc

the mods.dk web site has the manual:
http://www.mods.dk/manual.php?brand=marconi
You need to sign up though.

Peter

[orbanp1]

Originally Posted by kernowcam

More progress. I am looking for a signal at TP3 on RF amp board a3. Tr 4 and 6 seem to have the correct voltages, however pin 5 should have 6v which is the ALC control voltage. Its 2.5v.
I have been told as its a feedback loop may be tricky to fault find. The 2.5 v feeds to 2 FET's which then feed tr4/6. One has a 6.5v source feed from tr4 giving 3.5 at the drain, the other 6.5 from tr 6 giving 6.5 at drain. I am thinking the FET is short circuit and or the tant capacitor from drain to earth may have failed.

One way to test a circuit with a feedback loop is to open up the loop and then test the sections of the circuit.
In your case, e.g., open the circuit at pin-5 and add DC control voltage to it from an external source, and see what happens.

I am wondering if the schematics is correct regarding those TR5 and TR12 J-FETS (drain and source mixed up?). Those FETS are used as variable resistors for controlling the gain by adjusting the values of the emitter resistors of TR4 and TR6. The resistance of the FET is controlled by the source-gate voltage while the drain-source voltage should be around zero, that is why there are C28 and C32 capacitors. See http://users.ece.gatech.edu/~lanterm...fet_cvr_an.pdf
On the other hand, a linearizing circuit, like R47-C27, R50-C34 is usually used between the gate and drain in such a circuit.
In any event, either of those those C28 and C32 caps could be shorted, as you mentioned. Those tantalum caps could be replaced with a "regular" aluminum electrolytic capacitor, paralleled with a 100n disk capacitor.

Peter