ST 1700B

Jump to Latest
L

llwhtt

Member
Joined 2008
#1
My 1700B won't null intermittently, lightly tap the front near the "distortion" push button and it will null. I have verified the oscillator is OK. So my question is has anyone ignored the warning stickers inside and cleaned the switches with DeOxit?

Craig
 
#2
By now you probably need to clean them. Use the Caig lab contact lube stuff. those are all sliding contacts. Their concern was someone taking Freon tuner cleaner and blasting the switches. Without lube they would wear pretty fast.

Its quite a PITA to get at all of them. Check that it does null at other frequencies. You need to be sure its the switch and not something else. like another flakey connection. Also the cables unplug on pins that are known to corrode over a long time. Good luck.
 
#3
The last time I was in it, when this all started, I'm pretty sure I checked/reseated the connectors and anything else that was obvious. The only thing I didn't do was ignore all those stickers. I got this from James Bongiorno about a year before he passed and was supposedly fresh back cal. It's worked great until this problem. I'll get back in it when I get a chance.

Craig
 
#4
I mean this in the most respect to the late James Bongiorno, but does it smell like smoke / cigarettes or have smoke residue outside and inside? I sent him a tuner to calibrate in 2005 and it came back smelling like smoke / cigarettes. I worked on plenty of studio tape machines that had control panels turned brown in color due to smoke and smelled like an ash tray inside the card bays.

He had major health issue during his life. Smoking probably did not help.
 
#5
This piece is clean but yes he was a smoker and drinker. I'd been to his small apartment in Lompoc a couple of times and it was not a pleasant sight, though his little shop room seemed OK. I only met him after he'd mellowed out, I guess was quite the character back in the day. Kinda wish I'd met him earlier because I've got lots of questions about my SUMO "THE POWER".

Craig
 
#6
I am a big fan of his Ampzilla amps. I have several of the first generation. Along with a Son and Grandson. I saw his personal Ampzilla on eBay and a clear acrylic one from his collection on eBay after he passed away. Unfortunately at this point in my life they were too expensive for me.

That's cool you met him in person.

RIP James
 
#7
I have two Ampzilla IIa, Son, Grandson, Thaedra I and II, a Thalia I and a few SUMO pieces. I've never run across an original Ampzilla but then I don't go looking for them either. I have to keep my disease under control! I know JB wasn't a fan of the Ampzilla IIa but from I understand his last design, the II, wasn't very stable which seems odd as stability was always in his specs. He didn't care for the Thaedra II either. Both were after he left and other people "messed" with his designs. I really enjoy working on all of the old SAE/GAS/SUMO stuff.

Craig
 
#8
I finally dove into my 1700B and found several leads of the opto-couplers NOT soldered!!!!!! My board is different from the Stan Curtis manual that I downloaded. I have only three, that I can find, optos, instead of four. One of the CL60s has been replaced with a VTL5C4 and had at least two non-soldered legs. That is the middle position opto. The front position opto looks to be a plug-in since the the board has hollow turrets, I touched up the solder joints on that one as well. The intermittent nulling is gone now but still have high distortion readings in self test, unsteady .0055-.006 in the .03 position and off the scale in the .01 position. Since .0055-.006 is less than .01 it shouldn't peg the meter in the .01 position. Need to troubleshot the Ratio circuit now, any ideas?

Craig
 
#10
I would start by disabling the auto set level and verify gains at each setting. Useful to have a decade attenuator for that task. The VTL5C4 was the original replacement part when the CL60 ceased to be available. Try to match to a Silonex which have lower distortion. I have datasheets but won't have access until Sunday if you need them. Some variants used socket pins rather than soldering. The calibration says you need to wait 5 minutes or so before you can calibrate since the photocell takes quite a while to dark adjust.

I believe there is one photocell in the oscillator and two in the analyzer. Another in the auto set level circuit. With some careful opamp updating you can get very good performance from it. I found some adapter boards for TO5 to dip on eBay which enables the use of modern opamps but the Harris parts are very good to start with.
 
#12
Here's something interesting the meter pegs in the .01 Ratio position ONLY at the 1KHz and 2KHz frequencies or at least when the x100 and 10 or 20 buttons are pressed. At 4KHz I get an unsteady .0075-.0085%, still a tad high but at least it's not pegged. Back to the manual.

Craig
 
#13
Popped the ground fuse, disassembled, replaced fuse. Decided to ESR check all of the electrolytics and found both C306 and C310 dead, patched in some new caps and my problem on the .01 Ratio scale is gone, yippy! Need to order the correct capacitors now.
 
#14
llwhtt said:
My 1700B won't null intermittently, lightly tap the front near the "distortion" push button and it will null. I have verified the oscillator is OK. So my question is has anyone ignored the warning stickers inside and cleaned the switches with DeOxit?

Craig
Click to expand...

Did you ever get yours sorted out? We had many of these as well as the 1000A at my old job. My boss was an ace at keeping them going and always swore at their connectoritis. He went through many cans of Cramolin (DeOxit alt) returning them to service.
 
You must log in or register to reply here.
Top Bottom