Telefunken Italia - model "Mignonette MF" - 1a Serie

Telefunken Italia - model "Mignonette MF" - 1a Serie

JAN 2023 - restoration notes.

I don't want to bore you with information that is already available on the net about radio restorations and/or about this particular radio model.
I just want to share my restoration notes and annotated schematic.

This radio has the chassis directly connected to the power line.
There is a very HIGH risk of electrocution - use an isolation transformer when working with this kind of old radios.

Please note the use of an auto-transformer that imply no isolation from mains (!!) and as the power switch is directly connected to the power line. There is no fuse!
Everyone putting his hands into this chassis must know what he is doing!!

I started replacing all paper caps and the 3 electrolytics.
Then I replaced all the resistors that measured way out of specs. Some of them are unreachable (left alone).

This Italian radio makes use of one of the first attempts to integrate components on a single "chip": they are LARES boards.

Here are few examples:

Excerpt from LARES manual

Here are the ones I've replaced.

The units replaced

While it looked a good idea at that time to introduce simplification to the spaghetti layout approach of the time, it turned to a nightmare as time goes.
As many other noted on the net, they shift way out of specs with time and mine are  not exception. I replaced them all with discrete components.

The radio is working now: FM is really OK; on other bands it remains heavily deaf.
It probably needs a complete IF alignment  but I have no time left and I do not want to risk breaking the coil slugs (they are strongly glued and look very fragile).

Here is my annotated schematic diagram for you guys to enjoy.

LARES modules (NOR-323 and NOR-322) are highlighted.

Hope this help.
Ciao, Emanuele.

User manual:

 

 

 

Here are some unsorted pictures taken during the restoration process:

 

Adventest R3361B Spectrum Analyzer vertical instability fix (failed joint between input LPF and coupler)

After full recapping of the PSU and CRT modules of my R3361B the instrument began showing a pronounced vertical instability: looking at the CAL signal (30MHz / -20dBm) the trace was randomly jumping up and down in a 5-8 dB range.
I initially suspected a side effect of my recent recappings, but that was not the case.

Long story short:
during recapping I was forced to move/dismount/rotate/drag the unit multiple times..
In one of these movements I had to drag the instrument towards me: the two front feet inadvertently went over the edge of the table; it has been as if the instrument had fallen from a height of 2/3 cm hitting the table edge right on its bottom front part.
This has been the actual moment since the instability began to show up.

Stated that:
- the input LPF-coupler assembly is located just behind the input socket in the right bottom front part of the unit - just where it took the hit;
- the LPF (THP118) and the coupler (THP202) are each built as gold stripes laid down on a ceramic substrate; the two parts are connected via a very thin solder joint crossing between the two ceramic wafers.. 

(Image from eevblog forum, author Mr. "razberik")

 

 

 

I decided opening the RF input section , and....
BINGO!
the solder joint in my unit had flown off as you can see from this picture:

The unjoi"ned" joint

 

 

 

 

Here is the block diagram of the involved parts (the failed joint circled in red):

 

 

 

 

The problem was now how to fix it without significantly affecting the features of the instrument.
Doubts were about:
- the surface to solder is less then a couple of mm2;
- the material to be soldered is a thin layer of gold laid down on a ceramic support from which it can easily lift up by the effect of heat;
- the part is a VERY sensitive part and very high frequencies are involved there and so the geometry of the traces counts A LOT;
- Is it advisable to use some solder flux here??
- Is it advisable to put a very thin copper strand between the parts?
- how can we avoid the solder from spreading too much along the traces? (the gold plated traces transport tin very easily).

Here is an excerpt of the suggestions I've got from the eevblog forum:
- solder a thin copper strand between parts is OK and avisable;
- put kapton / polyimide tape on the areas that you don't want to have solder on;
- conservative tip heat setting, just enough to melt the solder and not much more;
- use hot air from the underside to pre-heat (evenly !) and then solder very carefully (unfeasible here as per hardware setup..);
- take your time; it is a repair where you can easily mess up it all;
- No lead free solder within 100 miles of this project!
- Paste flux, minimal quantity (speck on end of a toothpick)

With these suggestions in mind I proceeded against the unknown and started the procedure depicted by the following pictures:

..masking

  

..soldering

 

 

Finish!!

 

 

 

 

 

 

I didn't put any copper strand (too difficult in a so small fixture).
Final cosmetic result is not as good as I would have liked it to be; I had to use 400°C to get a good bright joint: it was like as the ceramic substrate was sinking a lot of heat. Due to lack of heat the solder lumped instead of spreading as expected.

I any case the S.A. is now stable again.
I should now check it for flatness on the entire frequency range but I do not have any suitable sig-gen... (I only have an HP8640B-no doubler..).
May be I can perform some test using the internal tracking generator.. will see.
For the frequency ranges I usually work on (< 0,5GHz) I believe this can be considered a success.
Conclusion:

Advantest spectrum analyzers must be treated like very fragile crystal glasses, absolutely preventing sharp hits, even if not very violent.

 

Hope this can help someone else with similar problem.
Emanuele.

NOTE: Someone drew my attention to the left side of the solder where a crack in the ceramic wafer is quite clearly visible; this is something I will address in the future. At the moment I don't see any problems in the functionality of my SA.

Advantest R3361B Spectrum Analyzer CRT module removal and recapping.

 

DISCLAIMER: the following instructions are provided only as a report of my hobby experience. In NO way they can be interpreted as a replacement of the Advantest service  manual instructions. In no way I am responsible of any damage you or your device can suffer by following this procedure. Lethal voltages are present in the device!! Qualified personnel only! You know what you are doing and you are proceeding at your own risk!

 

 

To get to the CRT module I have followed this procedure:

1. Place the rig in normal position.
   Remove the four plastic feet on the back: the top and bottom metal covers will now slide off. You have to remove both.
2. Disconnect the black connector located in the backplane board very close to the PSU cage right front edge. It is the power and video signals BUS going to the CRT module.
3. Remove the left side rib - the one with the handle (4 big screws 4 small screws); pay attention to the plastic termination at the back side of it: slide it off BEFORE attempting to remove the rib..
   You do not need to remove the card reader board (if that option is installed).
4. Remove the plastic bar present on the upper crosspiece of the front panel and remove the 3 small screws that retain the front panel.
5. Place the rig upside-down (from now on the left and right references are referred to this new position).
6. Look at the front panel bottom crosspiece and remove the 3 small screws that retain the front panel.
   You can now pull the front panel off but to completely remove it you need disconnect the ribbon cable from the controller board and the power wires from the power switch (take note of actual connections there..).
7. The CRT module is fixed to the main frame by mean of 4 screws located at the bottom side of the box (but you see them from the top as the rig is now upside-down).
   Two are visible and reachable directly through two holes in the front panel lower crosspiece and the third is visible behind a group of wires close to back left side of the TG. Remove them all.
8. Unfortunately to reach the fourth screw you need to unlock the tracking generator. It can seems scary but it is not so difficult then...
1. Remove the bottom front crosspiece completely removing 8 big screws; note that two of them are actually fastening the TG unit front part (just under the TG output connector..).
2. Disconnect the flat cable from the back of the TG. 2 bigger and longer screws remain to be removed: they are located at the back left and right sides of the TG unit.
   At this point the TG unit can be flipped over to top of the rig (..actually the bottom ...as it is upside-down) revealing that damned fourth screw. Remove it.
9. The CRT module should now be free to come off. Take care of all the wires while removing it.
10. Once you have the CRT module in your hands, unscrew all the 8 small screws (4 on one side, 4 the on other side) but do not touch the 2 bigger screws you see on the lower back of the unit.
11. At this point you can remove the entire CRT chassis out off the metal frame.
12. Should you want to separate the board from the chassis, disconnect the two wires bundles coming from the outside; disconnect the ground lead from the circuit at the CRT neck, unscrew the 4 nuts at the bottom side of the board.
    

You are now ready for recapping and redo solder joints.
Please note that C319  (10uF/25V)is a NON-polarized electrolytic.
Here is the cap list I used for recapping:

 I've left the snubbers C319, C207, C205 and all other high voltage caps alone as I was not able to find them at local suppliers and I didn't want to wait for an online dealer..

Some useful pics:

Step 2: Video connector

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Step 8.2: damn screw

 

 

Step 8.2: flipped TG unit

 

Final test before reassembling..