I restored the power supply, Deoxed the pots and switches. Replaced the RCA jacks on the front and resecured all the BNC connectors on the back.
All the PS voltages are good.
I have the panel connected to the ST1700B and a ST1000A along with the Bench receiver.
At first the test panel was working well. I connected each ST Distortion analyzer, FM generator and the Oscilloscope, making sure the switching and functions worked through the panel.
I have a feeling the op amps are making it difficult to precisely check the functions. Sometimes the signal is there, other times its distorted.
Its the buffered signal that the ST1200 uses for all the test functions where a signal is needed in the test receiver/amp.
It has some of these OPA2605 and the OPA741's there's 14 or so op-amps total in this piece of equipment. I need to find some modern op amps to fit.
Here's an attachment of the snip: test signal board:
All the PS voltages are good.
I have the panel connected to the ST1700B and a ST1000A along with the Bench receiver.
At first the test panel was working well. I connected each ST Distortion analyzer, FM generator and the Oscilloscope, making sure the switching and functions worked through the panel.
I have a feeling the op amps are making it difficult to precisely check the functions. Sometimes the signal is there, other times its distorted.
Its the buffered signal that the ST1200 uses for all the test functions where a signal is needed in the test receiver/amp.
It has some of these OPA2605 and the OPA741's there's 14 or so op-amps total in this piece of equipment. I need to find some modern op amps to fit.
Here's an attachment of the snip: test signal board:
Attachments
This ST1200A (J36) connects up to the ST1700A ( Source & THD analyzer) as its source and routes the signal to the test receiver.
The test receiver speakers connect to J9-12 to TB1 (1,2 & 1.9) o/p gets routed back to the ST1700A
check Relays K1,K2,K3 Speaker fuses F4,5
I think you need to trace/monitor the signals from input to output.
The test receiver speakers connect to J9-12 to TB1 (1,2 & 1.9) o/p gets routed back to the ST1700A
check Relays K1,K2,K3 Speaker fuses F4,5
I think you need to trace/monitor the signals from input to output.
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Working on the ST1200 is a real PITA. Much harder than the analyzers with all the myriad connections on the test panel. I have had some bad connection problems as well. They turned out to be the cable connection to the PCB's. Again deox helps as did NOT plugging in all the way??. Sometimes you just need to move on. Its been fine with the cable slightly loose.
First probable candidate are the switches. At their age they may have some corrosion on the contacts. replacing opamps is only a last resort if everything points at them. You can make an adapter using parts from e-bay. There are adapters for using can opamps in dip sockets but you can reverse that with the pins on the round pattern and sockets on the dip pattern.
I rescanned some of the pages that did not come out well. PM me and I'll resend them.
First probable candidate are the switches. At their age they may have some corrosion on the contacts. replacing opamps is only a last resort if everything points at them. You can make an adapter using parts from e-bay. There are adapters for using can opamps in dip sockets but you can reverse that with the pins on the round pattern and sockets on the dip pattern.
I rescanned some of the pages that did not come out well. PM me and I'll resend them.
I ended up cleaning all the connections. Using the Fader 5 for the switch lubrication.
The 1200 is working perfectly.
The one issue I wish I could I work out, if it’s even possible, is testing a Pre-amp. I can’t understand why I can’t get it to switch through the bench receiver.
I thought using the pre amp RCDR through the amp in, setting the Bench receiver to AUX, switching the Analyzer inputs to Rcdr?
In a nut shell:
Is it possible to connect a pre amp alone to the 1200?
The 1200 is working perfectly.
The one issue I wish I could I work out, if it’s even possible, is testing a Pre-amp. I can’t understand why I can’t get it to switch through the bench receiver.
I thought using the pre amp RCDR through the amp in, setting the Bench receiver to AUX, switching the Analyzer inputs to Rcdr?
In a nut shell:
Is it possible to connect a pre amp alone to the 1200?
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There's a cool factor to the whole ST thing. I have all the ST equipment that connects up to the 1200A and I'm still finding out about all the functions.
I like using the equipment and the level of simplicity it gives. Although it has a ton of connections and needs some attention from time to time.
There's nothing in the manuals explaining the connections and switching for a pre-amp only connection/test procedure. The only way is to have a separate amp sub'ed in. Not completely sure yet.
I like using the equipment and the level of simplicity it gives. Although it has a ton of connections and needs some attention from time to time.
There's nothing in the manuals explaining the connections and switching for a pre-amp only connection/test procedure. The only way is to have a separate amp sub'ed in. Not completely sure yet.
I took a quick look at the service manual for the ST1200A, it has an inverse RIAA filter, which means, it is able to test phono pre-amp frequency response accuracy among other tests.
I see on the 1200A front panel,
"To Amplifier Inputs" Phono, Aux/Tape, you connect these L/R outputs to the device, receiver/pre-amp under test (DUT), phono and/or tape and/or aux inputs
"From Amplifier Outputs" connect this to the pre-amp output jacks on the DUT outputs (pre-out).
If you want to run the amp too, use a "Y" cable to split the pre-amp out, back to DUT amp-in and to the ST1200. Connect the DUT speaker/amp-out to the 1200A speaker inputs.
Give it a try.
I see on the 1200A front panel,
"To Amplifier Inputs" Phono, Aux/Tape, you connect these L/R outputs to the device, receiver/pre-amp under test (DUT), phono and/or tape and/or aux inputs
"From Amplifier Outputs" connect this to the pre-amp output jacks on the DUT outputs (pre-out).
If you want to run the amp too, use a "Y" cable to split the pre-amp out, back to DUT amp-in and to the ST1200. Connect the DUT speaker/amp-out to the 1200A speaker inputs.
Give it a try.
The problem, not obvious from the schematics, is that there is no way to pass audio through a preamp and to the amp section of the attached receiver and then to speakers. Testing for distortion etc. is simple. but no option to listen the way its all set up. You could just pull out another amp and tie into the load/speaker connections. But that seems a little silly with a receiver already tied in.