DS345 func gen schematics (power supply problem)

[terryk87]

Hello all,

My Stanford DS345 function generator refused to power up, and the mains fuse was blown.

(1)
The manual is easy to find and even has operational descriptions and a parts list, but the schematics are in separate documents referred to as Sheets 1 to 7, and never seem to be included or alongside the manual.  Does anyone have them or a link, or have they been posted here?  (I did a search here on DS345 and didn't get anything.)

(2)
I've begun troubleshooting it blind, and have found that the fuse blows even w. the secondary windings of the main transformer disconnected from the board.  (These windings measure reasonably w. an ohmmeter.)

The primary winding(s) have wire colours (in order) brown, green, red, orange, yellow.  They are connected to a mains filter / fuse / 120 or 240 config module which I have not (yet) figured out.  However, I had disconnected these wires and measured the resistances of the primary winding(s) as follows:

brown to green: 28 ohm

red to orange: 23 ohm
orange to yellow: 7 ohm

Is that reasonable for primary windings?  (The asymmetric tap has me wondering.)  BTW, the transformer says "Pacific 1095 6-00092" but I couldn't find any data on that.

(BTW, when I had disconnected the primary windings, the fuse did not blow so the problem does not seem to be the "mains filter / fuse / 120 or 240 config module" I referred to above.)

(3)
If the problem is the transformer (as seems so at this point), I could perhaps hack in an alternate, but I'd have to know for sure what this one is supposed to be doing...

Thanks for any info or experience with this,
-Terry

[tautech]

Wondering if the mains filter is shorted? 
What type is it?
Pic?

Follow member xrunner's thread from here:
https://www.eevblog.com/forum/testgear/hp-54501a-restoration-and-calibration/msg941934/#msg941934

[terryk87]

Wondering if the mains filter is shorted? 

Unless you're referring to a different possibility, I noted that:

(BTW, when I had disconnected the primary windings, the fuse did not blow so the problem does not seem to be the "mains filter / fuse / 120 or 240 config module" I referred to above.)

So the short verson is: fails w. mains filter module connected to transformer primary windings (secondary windings NC); does not fail w. just mains filter module.

So I'm wondering if the transformer is gone, along with the resistances I measured on the primary windings.  Even so, the schematics would be helpful (e.g. to help spec an alt transformer to drive the regulators).

[tautech]

Try this manual link:
http://elektrotanya.com/srs_ds345_synthesized_1uhz-32mhz_function_10mhz_arbitrary_generator_sm.pdf/download.html
12.9 Mb

Wait for "processing" to change to "get manual".


PSU schematic on P142

Edit
And the best bit is all the transformer primary taps and secondary windings have all their voltages listed. Treble 

Further edit
check the listed 130VAC zener for short

And another edit
Above mentioned 130VAC zener is listed on P127 as: 4-00541-435 130V/1200A Varistor, Zinc Oxide Nonlinear Resistor
It can be safely omitted for tests.

[lowimpedance]

Try this manual link:
http://elektrotanya.com/srs_ds345_synthesized_1uhz-32mhz_function_10mhz_arbitrary_generator_sm.pdf/download.html
12.9 Mb

Wait for "processing" to change to "get manual".


PSU schematic on P142

Edit
And the best bit is all the transformer primary taps and secondary windings have all their voltages listed. Treble 

Stanford have the rather annoying habit of removing the schemattics from all their online manuals archives, but luckily they are provided with the paper manuals. And with a bit of luck someone will scan the diagrams for their gear and upload for all to share. I have a DS345 and gave up looking for the 'full' online version .......till now. Thanks for the link and 'reminder' !.

[tautech]

Try this manual link:
http://elektrotanya.com/srs_ds345_synthesized_1uhz-32mhz_function_10mhz_arbitrary_generator_sm.pdf/download.html
12.9 Mb

Wait for "processing" to change to "get manual".


PSU schematic on P142

Edit
And the best bit is all the transformer primary taps and secondary windings have all their voltages listed. Treble 

Stanford have the rather annoying habit of removing the schemattics from all their online manuals archives, but luckily they are provided with the paper manuals. And with a bit of luck someone will scan the diagrams for their gear and upload for all to share. I have a DS345 and gave up looking for the 'full' online version .......till now. Thanks for the link and 'reminder' !.

Well that one's a real doozey, beautiful schematics and surprisingly easy to find with a simple "DS345 service manual" Google search.
Just goes to show how they get updated from time to time, manuals that I thought were unobtainium are now available. 
Anyways, my pleasure and enjoy. 

[terryk87]

Thanks for the link to the service manual, tautech!

And the best bit is all the transformer primary taps and secondary windings have all their voltages listed. Treble 

...which is exactly the info I need, since:

SOLVED:
The problem was indeed the transformer.  Even though the windings measured OK resistance-wise, the primaries were drawing several amps w/o a load (on the secondaries).  IIUC this is likely excessive eddy current losses, presumably due to the insulation breaking down between the laminates (an age-related failure) - ?  (Clarifications or corrections welcome.)

Later I'll post the p/n of a currently-available replacement that is the most compatible I can find.

[rastro]

Any luck on finding a replacement power supply transformer???  I think I have a similar failure.

[SoundTech-LG]

Thanks for the link. I have a DS340. Do not see it at electrotanya, but the 345 may prove helpful.

[rastro]

I tried contacting SRS last week via email and phone message but have not gotten any response.   

[terryk87]

Hello all, I had intended to follow up on this, but you know, events...

At the time I quickly realized an equivalent or adaptable replacement for the transformer did not exist, so I replaced it w. three of those "configurable" types.*  I mounted them externally (bolted on top of the steel case) - it was ugly as sin but seemed worth it to keep that beast going.**

However at the same time I also found a bad filtering (smoothing) cap, also age-related but apparently indep. (not causitive) of the transformer failure.***  NOTE: it wouldn't surprise me if other units are experiencing this too.  In my case, I happened to catch it too late and it sunk the whole thing (but others may fare better).

The details:

One of the large electrolytic caps had been oozing corrosive gunk onto the PCB (this had been happening before I replaced the transformer).  I replaced the bad cap (and some of the others proactively), patched a couple of eaten-away tracks, and it worked – for awhile.  However I should have known better: if something had eaten the PCB, it was probably still eating it (it had looked like the damage was limited, but later I realized it was a multi-layer board...)

So for anyone else:

If you're trying to keep one of these things going it may be a good idea to replace the filtering caps.  However if the particularly ungraceful failure I had (corrosive leakage) was due to a particular model of cap, maybe it's only worth replacing this one (or probably pair, 1 for each phase).  At this moment all I can recall is that it had brown-coloured sheathing and was about 10 to 15 mm in diameter.

Also note that the power supply stages (incl. the regulators) are always on (i.e. even if the front-panel power switch is off), so if it's plugged in it's cooking (maybe this is for stability, since there's a precision reference involved?).

(footnotes)

*IIRC, from the Triad "World Series" (chassis mount).  BTW, all 3 gave me more secondary VAC than I believe was being spec'd, but maybe I missed that it was at a certain load (it certainly wasn't a case of mixing up RMS and p-p).  (I don't recall if it meant I could've gone lower in spec'd VAC(out) for any of the 3.)  I was worried about forcing the regs downstream to dissipate more than designed, but they didn't thermally shut down.  Also, the existing and new caps had adequate V-ratings.

**Even though it was only 30 MHz and had a more primitive UI, it had a floatable output.  It was also from the era when people knew that ergonomics included pushbutton action!  (Not like all the squishy crap we have now which if pressed off-centre isn't tactile and may not make contact, aurghhh!)

***At first it may seem curious that both failures happened around the same time, however this was while I had the unit plugged in for several weeks after it had been mothballed apparently for years, and since the power supplies are always on standby and both failures are likely age-related (bad filter cap and transformer presumably w. broken-down laminations), it's not suprising.

[rastro]

@ terryk87

Thanks for the update.  Sounds like you got a work around.  I'm also finding it unlikely to get a replacement part that meets size and voltage requirements.

Finally got hold of SRS tech support and was told they don't sell spares.  Evaluations and some level of repair started at about 1/3 of list price of the system.  So that's a dead end.

Since I want to keep the system as a contained unit my choices are limited.
1. Find an EI kit with comparable dimensions and wind my own.  Most of the kits are for audio/RF applications.
2. Find a toroid with the comparable outputs. Or build one that will fit in the system with a makeshift bracket. 
3. Disassemble the old EI transformer noting the wire gauge and winding count and rebuilding it.

I think option 3 seems like my best path.  Although taking apart the old EI is very difficult without damaging the core.  I've seen some youtube showing disassembley but I'm not having any luck with taping out the "E" pieces.  They are stuck.  So I figure I'll have to unwind the bobbin and maybe crack it off before I can disassemble the "EI" core laminates.

Right now I just finishing un-treading all the secondary.  After I un-thread the primary I am hoping to crack the plastic bobbin free of the EI core and can then peel off the EI layers.
This is probably going to be a while.

-rastro