Marconi signal generator repair ?

BillC

Active member
I have had this Marconi TF 2002 signal generator for many years , never tested, it was part of a larger testing unit ex mil. This unit does not have a power supply on board , but has the required voltage regulators fitted and will accept -16 to - 32 volts dc + to chassis (ground) from an external unregulated supply.
I brought the unit in from a storage situation, removed the covers, removed the mud wasp nests and gave it a general cleaning. There is some damage to a band switch wafer, should be able to straighten and reset the contact. Also two nylon split couplings on the band switch shaft have broken and the third one is looking very groggy. It might be possible to repair the unit, but I am sure that there will be many leaky capacitors and open circuit inductors in the output filter blocks. The tuning system uses slug tuning, the tuning shaft with pulleys and steel slug driving belts may be seen in one image.
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VK3ZYZ

Moderator
Staff member
Do you know what current it requires?
I have a power supply of 32V 940mA and 16V at 625mA you can have if it is suitable. It is -Ve common so just the 32V may be usable in this appliction.
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This if from an old HP printer so should be pretty good quality.

EDIT: I found the manual and it says 300mA so this power supply should be good. Mybe run it through a couple of diodes to drop the volts a little?
 

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BillC

Active member
Hi Denys, your power supplies look good . There is some unused space in the main chassis of the unit, so one of your PSU.s could be very handy. Thanks, I will try a few mechanical repairs to the band switch shaft couplings first.
 

BillC

Active member
I have superglued all the cracked and broken band switch shaft couplers. The shape and the profile of the coupling elements is complex and not easily copied by milling or turning, might have to try to change the coupler design a bit.? The couplers as made are really quite feeble and the mechanical strength is lacking with that particular setup. The clamp bolt is in the center of the coupling element and when tightened the effect is such that it bends the clamp pieces in the middle and that promotes cracking across and through the clamping hole , very poor idea destined to fail.
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VK3ZYZ

Moderator
Staff member
This could be a good use for 3D printing, to make some new ones.
I mainly use PLA but ABS may be ok too. But the best I think would be Carbon Fiber Nylon.
Maybe a couple of Aluminum half tubes around the plastic bits for reinforcement will work?
 
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BillC

Active member
Hi Denys, the switch shafts measure 3.9 x 2 mil so that means the shafts are flat section. The shaft is divided into separate sections and driven by the insulated split couplings presumably to stop inbreeding of the RF signal between stages which could possibly couple along a common shaft. The actual shape of each coupling unit is fairly complex even with a small pip moulded into the center of the flat section at each end of the coupling piece, there is a corresponding hole in each end of the switch shaft and on assembly when the two halves of the coupler clamp together and the pips engage with the holes in the shaft sections the required lineal distance is achieved, this happens on four pieces of band switch shaft with three couplers. The couplers measure 13.2 mil long x 8.3 mil Dia. So the whole thing is fairly fiddly to work on. Your idea of an aluminium reinforcement is good, but there are space constraints so at this stage I hope to use circlips one on each end of the couplers to provide the necessary closing force for the split, this should put the clamping effect at the ends of the couplers so as to oppose the bursting effect as the band switch is rotated. With all this in mind I hope that the superglue repairs hold, and that the circlips do most of the work. COMPLEX is it not?? Thanks for the interest.
 

BillC

Active member
Thanks Ray,I will bring the Sig Gen and parts across to the meeting and we can check it out.
 

BillC

Active member
The newly printed shaft couplers fit and work perfectly, thanks very much for the fine job Ray. I used the couplers with the longitudinal print pattern, and have plenty of spares remaining too. I used 2 mm clamping bolts and at this stage will not use circlips at the ends of the couplers as the printed units seem to be very strong. Your printer must have a very fine print resolution. The next challenge with the generator will be to get the electronics to work, thanks for the help!! The images show couplers being fitted. Also a small drop of thread locking compound has been applied to the clamp bolts.
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VK3YNV

Administrator
Staff member
Looks like they worked out ok, the material is PET-G, which is similar to the PET that they make coke bottles from.
 
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