Systron-Donner 1702 sig gen. - UK Vintage Radio Repair and Restoration Discussion Forum

majoconz · 4th Dec 2017, 9:45 am

It may turn out to be a lemon, but it's only an NZ$15 lemon! Systron-Donner 1702 sig gen - 100Hz to 1GHz apparently.
Beautifully made in 1981 - mainly 74LS series logic and TO5 tin can analogue IC's - been stored in a damp place with lots of condensation inside the cast aluminium board enclosure - the cadmium plate had started to go off so that was carefully brushed out and vacuumed - the boards were all taken out and left outside in the sun for a couple of days. Mains power fuse popped and a couple of diodes in the power supply but is showing signs of life - the master oscillator is going - only couple of cycles down in 10MHz according to my HP3586A.

I've been working my way slowly through the test procedure - but it only tells you what to look for when it's right, not what to do when it's wrong. Many phase locked loops all tied back to the master oscillator - many tests say 'short this test point to ground and test that the lock light goes out' - trouble is, mine's out all the time! It has great promise and I haven't found anything disastrously wrong, but why doesn't it go....

...and it's frustrating that someone flogged the extension board!

KeithsTV · 4th Dec 2017, 1:59 pm

I acquired a Farnell sig gen about 20 years ago with a fault. It's only 10MHz to 520MHz and uses, from memory, 8 separate oscillators each of which is selected depending on the frequency set on the thumbwheels. It showed no sign of locking which was, after some signal tracing down to the 100Hz reference signal for the PLLs being shorted to ground by a faulty feed through cap.

As it's not locking on any range I'd suggest tracing the master oscillator signal through the various divider stages to make sure the reference to the PLL phase detector, which may well be 100Hz or 50Hz, is present. Then look for any output from the divider chain from the VCOs. There may well be more than one phase detector because of the wide frequency range.

I know what you mean about the missing extension board!! You may have to solder wires to the various points you need to monitor before making measurements. But for $15 you can't complain.

Keith

Andrew2 · 4th Dec 2017, 2:14 pm

I used to have a 1702 about 20 years ago. 100 Hz to 1 GHz in 100 Hz steps, all with thumbwheel switches! The only fault was a transistor in the attenuator driver and once that was replaced it worked a treat. A heavyweight though.

4th Dec 2017, 9:45 am	#1
majoconz Heptode Join Date: Jan 2008 Location: Ashhurst, Manawatu, New Zealand Posts: 570	Systron-Donner 1702 sig gen. It may turn out to be a lemon, but it's only an NZ$15 lemon! Systron-Donner 1702 sig gen - 100Hz to 1GHz apparently. Beautifully made in 1981 - mainly 74LS series logic and TO5 tin can analogue IC's - been stored in a damp place with lots of condensation inside the cast aluminium board enclosure - the cadmium plate had started to go off so that was carefully brushed out and vacuumed - the boards were all taken out and left outside in the sun for a couple of days. Mains power fuse popped and a couple of diodes in the power supply but is showing signs of life - the master oscillator is going - only couple of cycles down in 10MHz according to my HP3586A. I've been working my way slowly through the test procedure - but it only tells you what to look for when it's right, not what to do when it's wrong. Many phase locked loops all tied back to the master oscillator - many tests say 'short this test point to ground and test that the lock light goes out' - trouble is, mine's out all the time! It has great promise and I haven't found anything disastrously wrong, but why doesn't it go.... ...and it's frustrating that someone flogged the extension board! Attached Thumbnails __________________ Cheers - Martin ZL2MC

4th Dec 2017, 1:59 pm	#2
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,573	Re: Systron-Donner 1702 sig gen. I acquired a Farnell sig gen about 20 years ago with a fault. It's only 10MHz to 520MHz and uses, from memory, 8 separate oscillators each of which is selected depending on the frequency set on the thumbwheels. It showed no sign of locking which was, after some signal tracing down to the 100Hz reference signal for the PLLs being shorted to ground by a faulty feed through cap. As it's not locking on any range I'd suggest tracing the master oscillator signal through the various divider stages to make sure the reference to the PLL phase detector, which may well be 100Hz or 50Hz, is present. Then look for any output from the divider chain from the VCOs. There may well be more than one phase detector because of the wide frequency range. I know what you mean about the missing extension board!! You may have to solder wires to the various points you need to monitor before making measurements. But for $15 you can't complain. Keith

4th Dec 2017, 2:14 pm	#3
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,036	Re: Systron-Donner 1702 sig gen. I used to have a 1702 about 20 years ago. 100 Hz to 1 GHz in 100 Hz steps, all with thumbwheel switches! The only fault was a transistor in the attenuator driver and once that was replaced it worked a treat. A heavyweight though. __________________ Andy G1HBE.