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Old 2nd Oct 2022, 11:04 pm   #1
murphyv310
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Default Farnell SSG 520 signal generator

Hi.
I've obtained one of these fine Signal Generators.
Unfortunately I have a few issues and am looking for advice with the problems.
On initial power up the red out of range light came on but the green lock light stayed out.
After a few tests it was ascertained that although RF was present on the output socket it was way off frequency, setting the thumb wheels there was no change in frequency which was floating around 18.2Mhz.
Then all stopped, no RF the green lock light came on no matter what you do with the thumb wheels, also the out of range LED no longer comes on.
I then did some tests and found the +15v supply was missing, a short on the line after I removed the power connector so I had 15v from the 7815 regulator.
The short was traced to a very odd fault, the pvc tape on the lead from the plug was a like goo, it had melted into the PVC wiring and causing shorts all over the place, I've since repaired this but I've no lock nor frequency settings.
RF is present but it drifts all of the place.
Any advice would be helpful, I have the full manual.
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Old 2nd Oct 2022, 11:20 pm   #2
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Default Re: Farnell SSG 520 signal generator

The case of the galloping plasticiser.

David
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Old 2nd Oct 2022, 11:40 pm   #3
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Default Re: Farnell SSG 520 signal generator

I have a similar PSG520 and when I first acquired it in the 1990s I found it was failing to lock. I contacted the seller who said it sounded like a probable problem with the 'PAD diodes' and kindly sent me a pair of them FOC. I fitted them and that fixed the fault. This obviously must have been a relatively common 'stock' fault on them for the seller to be able to be so confident that that would be the fault. Of course there is no guarantee that this will be the problem with your unit.

Try searching this forum for SSG520 and PSG520 threads, there have been a few over the years and they may give you some leads.
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Old 3rd Oct 2022, 3:50 pm   #4
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Default Re: Farnell SSG 520 signal generator

Thanks chaps for the replies.
Looks as if the wiring loom is still a problem with another two supplies acting up, pressing the cables further downstream and the 5v and 22v lines drop out with noise showing on the scope most of the time on these two lines.
Not sure yet the best way to proceed as these feeds are via screened leads.
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Old 3rd Oct 2022, 9:06 pm   #5
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Default Re: Farnell SSG 520 signal generator

The PSG520 had plug in connector strips (brownish in colour) that were prone to being intermittent. Especially the ones on the psu.
I don't know if the SSG520 uses the same connectors.
The pins were ISTR tinned and tarnished over time. I used a fibre tip brush to clean them up and possibly a light coat of servisol?
Rob
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Old 3rd Oct 2022, 10:08 pm   #6
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Default Re: Farnell SSG 520 signal generator

Hi.
Some progress tonight. On the occasions that I did get some output I found when you gave the RF box a tap the RF would disappear. I then removed the cover and found two Tantalum caps rather warm, in fact one was getting quite hot, between boards there are five in all. They had to go! all went well but on the amplifier board on removal (rather fiddly with with the solid coax connection to remove one of the screened leads earth was off, this is a return for a supply ground, work has been done on the board in the past. on assembly I was rewarded with RF and tapping the RF enclosure it's now rock steady.
We still have problems and its from the Thumbwheels to the edge connector to the PCB. So Rob you could well be right or it's a wiring problem, one lead has been hard wired in the past. Hopefully tomorrow I'll be able to investigate and perhaps get a fix.
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Old 4th Oct 2022, 7:22 pm   #7
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Default Re: Farnell SSG 520 signal generator

Hi.
Slow but further progress today. Discovered more cable issues. The problem is on the joints of the cables, the screened cables being the worst, whatever the material is on the sleeves its deforming and corroding the joint its supposed to be protecting, three screened cables that go the the Synth board via the edge connector have turned out be at fault, I now have some control on frequency using the thumb wheels but there is no response from the four sub 1Mhz adjustments and the frequency is still way off also the FM section isn't working, could be due to lack of the start pulse, possibly due to incorrect locking. The green lock light is constantly on which is wrong but the out of range lamp is now operating as it should. With the Synth board out the RF is outing at 8.5Mhz but it does drift a lot.
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Old 6th Oct 2022, 10:08 am   #8
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Default Re: Farnell SSG 520 signal generator

Hi
After finding more issues with the cabling yesterday I boxed up the generator for another day.
I might try to obtain another with decent cabling hopefully unaffected by this unfortunate problem that is otherwise faulty and make one out of two.
Most likely put a wanted up and will see what transpires.
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Last edited by murphyv310; 6th Oct 2022 at 10:34 am.
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Old 18th Nov 2022, 10:18 pm   #9
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Default Re: Farnell SSG 520 signal generator

Hi
Well after banging the back of my hand when doing some other type of DIY that I can't mention here I was putting off further work on the generator. So I decided to power it back on and there was an almighty bang.
You may ask what happened, indeed it has suffered a catastrophic failure. Again cable form issues and the +24v line has shorted to the +5v line, this blew a bit of print in the PSU and has damaged virtually every board. I've now abandoned this and it's now in my late friend Bob's workshop in Sorn Ayrshire, the plan is one day to revamp the workshop to a display of a TV and Radio workshop (hence donating the generator) as it's no longer running, well that's the plan but who knows if it will materialise.
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Old 19th Nov 2022, 9:29 am   #10
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Default Re: Farnell SSG 520 signal generator

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Old 19th Nov 2022, 10:46 am   #11
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Default Re: Farnell SSG 520 signal generator

Quote:
Originally Posted by peter_scott View Post
Peter
Indeed a pity Peter but perhaps a warning to others with these generators to look out for this degradation.
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Old 19th Nov 2022, 1:31 pm   #12
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Default Re: Farnell SSG 520 signal generator

Hi!

I have a PSG520 so I will strip out all the cableforms and wiring and give them a most meticulous examination!

I have to admit in all the years I have worked on equipment dating from the 1950s to the 1990s I have never come across plasticiser migrating to such a severe extent as to cause short circuits that cause irreparable damage like that suffered in the OP's unit tho!

Most of the faults I've had with ancient p.v.c. wiring have been due to the insulation hardening & crumbling off!

I dismantled a Cossor CDU130 Oscilloscope for parts and drawing out, and the tightly–laced cableforms from this were all found to be in perfect condition!

Chris Williams
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