Marconi TF2171 Possible Problem?

[Timmus66]

Good afternoon,

I have recently acquired a Marconi TF2171 Digital Synchronizer unit to go with my Marconi TF2015 signal generator, I have two TF2015’s and have tried them both with the TF2171.

When the TF2171 is cold and first switched on and locked in to a frequency, the frequency readout on my counter is reasonably stable, after about 30 minutes or so of warm up time one would expect the unit to be even more stable or at least as stable, however this does not seem to be the case, after warm up the unit seems more unstable and the frequency readout seem to jump and dance about a fair bit.

Only having used this unit for a few days and not being that familiar with it I am wondering if this a normal characteristic of the TF2171 or if I need to investigate a bit? (capacitor issue maybe?), Any advice from those who have owned or used the same unit would be very much appreciated.

I have made two short video clips to show the problem, The first one is switched on from cold and the second one is after 30 minutes of warm up time.

https://www.youtube.com/watch?v=Pvy_...ature=youtu.be

https://www.youtube.com/watch?v=RmPY0hJhCso


Thanks in advance

Tim

[ronbryan]

Is the TF2171 'Sync Output' meter deflection steady and centred in both scenarios, or has the reading drifted off to one side or the other as the TF2015 warms up?

Is the TF2171 'Out of Lock' lamp unlit or flickering?

Ron

[Timmus66]

Sorry Ron, I should have included that information in my opening post.

Just to clarify, I have tested the TF2171 on both of my TF2015’s, both 2015’s were warmed up for two hours before the 2171 was switched on, the first video clip shows a warm 2015 with a cold 2171 and the second video shows a warm 2015 and a warm 2171 if that makes any sense?

Meters on both the 2015 and the 2171 were centered and steady and the out of lock lamp was unlit and not flickering at all, seems as the 2171 starts to warm up the instability starts.

Tim

[ronbryan]

If you have the manual, I would check the DC supplies are within limits. To make sure that the pre-scaler chip is getting enough RF signal, you could go through the input amplifier calibration procedure, adjusting R19 if necessary.

If you put an AC coupled scope at a fairly high gain setting on the 'Sync Out' connection, when the generator is locked, what does the control voltage look like? I think the design provides a current output, to be fed into a summing network in the TF2015, but it might give a clue if the variation is random, rather than periodic.

Although you have two TF2015 signal generators, which should eliminate a problem with that area, I have had an unsoldered connection to the 'Counter Out' connector, which gave low amplitude to that signal, which is used as the input to the TF2017. It should be no problem to check that you are getting >80mV output into 50 ohm from that point - in fact I'm sure that my generator gave more like 300mV once working properly.

I cannot remember for certain, but I think there are some 'vias' on the top logic board, possibly on power supply rails, that might need checking or re-soldering. Maybe someone else can clarify that.

If all else fails, you could go through the 'Circuit Checks and Adjustments' in the manual. The only other fault I have had with my unit is with one of the BCY71 transistors in the output amplifier, but in that case the fault was not the same.

Ron

[jimmc101]

This thread on repairing a TF2171 may be of interest.

Jim

[Station X]

Timmus66.

If you need the manuals please PM me with your email address. They're too big to post here.

[Timmus66]

Thank you for the replies and advice, I do have the manuals so tomorrow I will open her up and go through the maintenance procedure and take some test readings and give her a good visual examination for dry joints etc.

Hopefully I will be able to report back with some good news.

Again, thanks for the help.

Tim

[Timmus66]

A bit of a development, I started to check the DC voltages as recommended by Ron, all voltages on the A4 board checked out OK with the exception of pin 18, the manual states it should be set at 5.25v, on checking it was at 5.31v (slightly lower with the wire reconnected at 5.29v), so adjusting R3 to bring it to 5.25v I decided to try the set and noticed there was a slight improvement, with that in mind I reduced the voltage in small steps and found that at exactly 5v the unit was perfectly stable when warm (been on for well over an hour now).

Is it possible the 5.25v in the manual could be an error and it should be 5v or could this point to a problem elsewhere?

Tim

[ronbryan]

A lot of the logic in the TF2171 is the obsolete, late 1960's, power hungry 74H series, so I expect that the 5.25V specified at the power supply pins was to allow a bit of volt-drop in the interconnecting wires and the pcb traces. I think that 74H was designed for 4.75V to 5.25V at the chip itself. In addition to the 74H TTL, the Plessey ECL pre-scaler chips run very hot and are powered from the 5.25V supply, so may benefit from a bit less dissipation. You could always check to see if the pre-scaler drive amplitude is adjusted correctly (R19)

Ron

[Timmus66]

Thanks for the reply Ron, happy to report most of the checks I have carried out on it have been OK, only thing worth noting is that R19 was already at full adjustment.

It has been on most of the day whilst I have carried out tests etc. and has not missed a heartbeat, everything works as it should and it seems to be very stable now since setting the voltage to 5v on pin 18 so for now I shall call it job done.

A video showing how stable it is now when fully warmed up, I’m very happy with that.

https://youtu.be/7rTTWFVXWpo


Many thanks for your help, very much appreciated.

Tim