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Old 23rd November 2009, 10:09 PM   #1
diyAudio Member
 
Join Date: Jul 2009
Location: Boston & Shanghai
Default Any tips on ST-1700B Distortion Analyzer repairs..?

Anybody an eggspurt on Sound Technology ST-1700B type analyzers?

I'm trying to fix up a semi-functional one and discovering as often happens that it was less fuctional than I thought...

Replacing the obsolete LDR's (LED-photocells) with current Perkin Elmer parts seems to have mostly worked to put the oscillator back in service but in the process maybe has thrown a few voltages off. I was mostly winging it with that sub so don't have any reference for circuit mods to tweak, maybe there are a few things I need to do...

On the Analyzer side of the unit it still shows excessively high distortion readings, but I need to finish replacing those LDR's and then walk back through the voltage calibration checks again before I'm completely out of ideas...

Am considering upgrading the Op-amps via TO-99 to DIP8 adapters as well - I have googled the (thin) info that's available on upgrading those but aside from some ancient posts about AD744 and AD797 no specific details seem to be floating around.

Anybody know anything about servicing these or anybody who does? (Obviously I'm after self-service direction and/or mod/update info not send-it-out service - I know Sound Technology still will do calibrations and repairs to these but it costs a fortune and I'm in it to fix it myself anyway...)

Thanks in advance...
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Old 23rd November 2009, 11:19 PM   #2
Apex Jr is offline Apex Jr  United States
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Join Date: Jun 2002
Location: Torrance, Calif
Oh.. This brings back memorys...
I had bought 5 of these and had pre-sold them to Groove Tubes
he kept 3 and sold the other 2 to SWR. I had them calibrated
and the tech at Groove tubes said 1 was just not right, I took
it back for calibration twice and they told me it was fine.
They refunded my calibration cost.
I had to send it up to Northern California and to calibrate it
they wanted $600.00. there went my profit.
I was told it was the LDR and they had to replace the resistor
a 3 - 5 cent resistor ! ! ! Yes, they need to know what value
But $600.00.
I did satify the customer.

Steve @ Apex Jr.
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Old 29th November 2009, 10:35 PM   #3
jblmar is offline jblmar  United States
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Join Date: Dec 2005
Location: Brooklyn, New York
Try this.
Disconnect every section of the set except the oscillator. Take voltage measurements.
Reconnect the oscillator section, disconnect the other sections. Take voltage measurements.
Measure one section at a time.
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