Sound Technology 1700B

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ST1700 LDRs

I am working on three ST1700B, one with 003, & 004 options.
My plan to replace LDRs is based on the CLM6000 data sheet.
I am guessing that the CLM6000 (sorted by grade) was used in all
locations. { This may be WRONG } But gotta start from some point.

Here is the information I have collected: (Sorry TABs don't work)

U7 OSC PCB, , OSC GAIN CTRL , R Parallel 10K ,RED Grade 2, NSL-32
U205 DISTPCB, NOTCH , Phase Null , R Parallel 33K ,BROWN Grade 1, NSL-32
U206 DISTPCB, NOTCH , Amplitude Null , R Parallel 2K2 ,YELLOW Grade 4, NSL-32
U207 DISTPCB, NOTCH , R Switch , As SW ,BLUE Grade 6, NSL-32SR(2or3)
U208 DISTPCB, NOTCH , R Switch , As SW ,BLUE Grade 6, NSL-32SR(2or3)

DigiKey Price Ron Roff Trise Tfall Ifma Vf
CLM6000 500 500K 3.5 500 40 2.0 Original, likely all with sorting
NSL-28 $10.87 400 10M 5 80 40 2.5
NSL-32 $ 3.26 500 500k 3.5 500 40 2.5 x
NSL-32SR2 $ 3.45 40 25M 5 80 20 2.5
NSL-32SR3 $ 3.24 60 25M 5 10 25 2.5 x
NSL-32H-103 $ 3.14 750++ 500K 35 500 40 2.0

U207 - Relay + Resistor possible alternate
U208 - Relay + Resistor possible alternate

So I will try out the NSL-32 in the analog targets,
and the NSL-32SR(2or3) in the switching applications.
 
Good idea, thanks. I was looking around on Mouser and the options for PCB pin/sockets is mind boggling. My reason for putting in sockets is I don't know how many more replacements can be done before the PCB takes a hit, better safe than sorry. Plus it would be a lot easier to swap out the different replacement LDR's as has been mentioned above to see which ones work the best.
 
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Can you share a picture of the pcb that's different from the drawings? Ill look through my manual collection for clues.

Plotting the LDR's is difficult do to the time delays and some temperature sensitivities. Constellation does this for their volume controls.
 
Early ST1700

Thanks for responding. The photo shows two LDRs where I would expect three.
 

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Hi djwdjw
Here is what I did for matching LDR’s many years ago. It was a single one time test system. With today’s parts it could be different. I used an Audio Precision System One, DCX127 and an interface box to select parts. The DCX can measure Resistance while controlling the Current and plot it as Resistance vs Current. I have attached what I used as a controlled current source. I hope this may give you some help getting to your test fixture up and running.
I talked about this in post #13
Duke
 

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Future LDR curves

Hey Duke,
Thanks for the notes. I have already purchased some inexpensive DACs, & ADCs.
I will pair these with an Arduino DUE, and perhaps an FPGA - that is probably overkill.
I have a fair amount of experience with this type of task, and often over do the design work, but hey that is who I am.
AND that is why I have many unfinished projects.
This task has been a bit delayed by the death of my mother, and now I have three lawns
to mow and two houses to sell,.... So it may be a few weeks or months before I get this all done. My goal is to test and compare the
LDRs, and produce Spice models for the available parts. Now this is making a lot of work for myself, but as I am now mostly retired, (EE),
It gives me something to think about and push forward. Also it is fun!
I am interested in DIY conversations with people with similar interests.
Rambling: that is why I am posting here. It may come to pass that I also produce a YouTube channel featuring things like this.
If people are interested I will post links to that if it is appropriate here. Thank you for your suggestions and sharing your work.
That is what make sites like this work.
Dan
 
It has been about 8 months....so

Hey Duke,

This task has been a bit delayed by the death of my mother, and now I have three lawns
to mow and two houses to sell,.... So it may be a few weeks or months before I get this all done. My goal is to test and compare the LDRs, and produce Spice models for the available parts. Now this is making a lot of work for myself, but as I am now mostly retired, (EE),
It gives me something to think about and push forward. Also it is fun!
I am interested in DIY conversations with people with similar interests.
Rambling: that is why I am posting here. It may come to pass that I also produce a YouTube channel featuring things like this.
If people are interested I will post links to that if it is appropriate here. Thank you for your suggestions and sharing your work.
That is what make sites like this work.
Dan



I don't mean to steal or shift the away from the ST-1700 sets, but I think the 1700 and 1701 and 1710 units have a lot in common, and I am currently working on my first 1710a.

I used to work in a shielded room many decades back, where the ST-1700B was my main piece of test equipment, as I evaluated prototypes before they were accepted for purchase. Some had glue and ice cream sticks holding the circuit boards in place, so when I say - prototypes, some were very early indeed!

Any way skip to 37 years later and my 1710A with option 003. It doesn't work. Meter needle vibrates in a nasty way, and the generator output looks like a large sine-wave decreasing to nothing. I just ordered some 8 pin Dip to TO-99 adapters so I can try replacing the old Harris 2605 and/or 2625 cans or whatever they are, with more modern chips like the NE5534AN, AD747, LT1468CN8's, or LME49710 parts as appropriate. The outside of this set looks gawd awful, but the inside was pristine (except for one dead bug of a worm sort, like what I used to find in old Akai Reel to Reels).

I hope a few people will suggest some areas to check, and come Monday I will order some NSL32SR3 opto's, (or was it the 32SR2 that was found to be the closest to the original)???

Photo is from "input monitor". Input control is on .3 AC volts, Ratio on "0". I believe it is set to 1 kHz. X10, 100, 0, 0. 3 red LEDs are lit - OSC, Notch, Overload... I am at a loss.

I replaced the GEN fuse holder it was broken but the fuse was not blown 1/32 A. The +15 and -15 PS are adjusted to exact 15.00v. Not sure where to measure the +/- 17 volts lines (under a shield?).

I will not try to reinvent the wheel here, but I would like to get this working, so I hope a lot of people who know these sets better than I do - have many suggestions. Suggestions?


Steven
 

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Hi Steven,

I have no experience with Sound Technology sets but enjoy trouble shooting old test equipment.

I found a manual at the site linked below:

http://www.steampoweredradio.com/pdf/sound technology/sound technology model 1710a manual.pdf

Does it look appropriate to your set? Assuming it is, I'd start by poking around in the oscillator section.

I surmise the picture is a startup transient from the oscillator? It's encouraging that it at least starts. Best guess is that something has failed in the oscillator level control circuit. Would you try to capture the corresponding control signals at TP 1 and TP6?

Good luck!
 
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The ST oscillators have 2 modes, fast and low distortion. In the low distortion it settles in the fast mode and switches to low distortion after some time. The fast mode uses a Jfet and low distortion uses the optocoupler. You may have an open optocoupler. It may be in sockets so some wiggling might get that back. If you switch to fast does the oscillator work OK?
 
Hi Steven,

I have no experience with Sound Technology sets but enjoy trouble shooting old test equipment.

I found a manual at the site linked below:

http://www.steampoweredradio.com/pdf/sound technology/sound technology model 1710a manual.pdf

Does it look appropriate to your set? Assuming it is, I'd start by poking around in the oscillator section.

I surmise the picture is a startup transient from the oscillator? It's encouraging that it at least starts. Best guess is that something has failed in the oscillator level control circuit. Would you try to capture the corresponding control signals at TP 1 and TP6?

Good luck!



It has been a few days, and I already had that 1710A manual, but barely got 25 pages into it. I did locate the +17 / -17 supplies, under a big shield, and the -17 was -16.98 very close to -17, but the +17 was running an inconsistent +21, +22 volts so I suspect a shorted 2N3055 pass transistor or other problem.

Maybe the regulator IC, an LM723CL, it says 723CL in my set, and it's a ceramic mil spec part so I will try to check the 2N3055 first, problem is short leads on the output wires don't allow good access to this board, so some unsoldering wires first, before I can do any work checking various parts. On what board would I find those "test points" TP1 & TP6 ???


-Steven
 

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The ST oscillators have 2 modes, fast and low distortion. In the low distortion it settles in the fast mode and switches to low distortion after some time. The fast mode uses a Jfet and low distortion uses the optocoupler. You may have an open optocoupler. It may be in sockets so some wiggling might get that back. If you switch to fast does the oscillator work OK?



Hi Demian,

As far as I can see, the set is just running haywire, with the meter needle vibrating, and various LEDs on the front panel lit. Fast mode / Low Distortion mode it's the same - Crap!

Just discovered a PS problem, on the +17 volt line running 21 / 22 volts, not sure what else yet. All the optocouplers I have noticed are soldered (so far). I do mean to order some spare optocouplers, was it determined I think elsewhere that of the modern available replacements, the LUNA NSL-32SR2 or 32SR3 was the most appropriate, or the best?

Does the modern replacement part need a 120 ohm series resistor on the led side, I seem to recall someone saying something like that, or was it needed in series on the cell side?

Anyone recall what that other thread said on the subject?

Thanks,

-Steven
 
Hi Steven,

Are pins on U601 accessible for probing? I nearly always try to diagnose problems in-circuit.

A shorted pass transistor will likely present some odd voltages that would be observable at the regulator IC. Since the -17V regulator is essentially identical and is working, you can use it a guide to normal voltages. I suggest connecting your voltmeter negative lead to the -15V rail and recording observed voltages on all U602 pins. You should see nearly identical voltages on U601 re its ground terminal. The discrepancies should point the way. If you have trouble interpreting what you discover, I can try to help.

We can hope that repairing the +17 regulator will lead to better behavior elsewhere in the instrument. ;)
(BTW, I think I saw it's supposed to be set to +17.3V)

The test points mentioned earlier are in the oscillator section, and are the outputs of opamps U2 and U3.

Good luck!
 
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