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Old 27th August 2006, 11:26 PM   #1
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Default SG505 puzzle

my Textronix SG505 had been operating as close to perfectly as one could imagine until this afternoon -- now we have some 120Hz problems -- has anyone ever had the internal +/- 15 V regulation system on this thing go wonky?
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Old 27th August 2006, 11:31 PM   #2
anatech is offline anatech  Canada
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Hi jackinnj,
Like everything else, yes. How old did you say they were?

The repair is very straight forward and unlikely to affect the calibration, unless the 120 Hz residual was not found at the time of it's last cal.

-Chris

Edit: check your rack / supply also.
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Old 28th August 2006, 01:25 AM   #3
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yeah, I will check the pass transistors on the TM5006 before I start screwing around with the SG505 -- I had looked at the residuals back in the early summer and it wasn't a problem at that time so it must be the mainframe. the SG505 was yielding THD of 0.0005% to 0.0008% back at the time I did the article on the Super Oscillator.

the TEK mainframe is on almost all the time.
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Old 28th August 2006, 01:32 AM   #4
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Hi jackinnj,
At least you have a simple problem!

-Chris
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Old 28th August 2006, 04:36 PM   #5
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fwiw -- here's the power supply regulator used in the SG505 -- Q2 and Q3 are located in the TM5006 chasis:

Click the image to open in full size.
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Old 28th August 2006, 10:22 PM   #6
anatech is offline anatech  Canada
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Hi jackinnj,
Did you find the fault?

Wishing you success ......

-Chris
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Old 29th August 2006, 12:09 AM   #7
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yes, it was the F29555, F30555 pass transistors -- insulated TO-220 versions of the ubiquitous power supply transistors. I also gave the TM5006 a good airing with the compressor.
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Old 29th August 2006, 01:01 AM   #8
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Both?
Interesting.
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Old 29th August 2006, 02:11 AM   #9
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I didn't bother to check -- the SG505 worked well in all the other bays -- for the moment I have replaced the 2955/3055 with another On-Semi device of which I have thousands.

I have an SG502 which is completely dead -- some of the physical construction is identical to the SG505 but the 502 dates from 1971 -- this could be an interesting fixer-upper.
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Old 29th August 2006, 02:16 AM   #10
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I have a couple Tek modules but no rack. Would you sell your 502? I don't mind fixer upper.

-Chris
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