Problem with Otari MTR-90 MKII 2" 24ch Deck

kfalls · Aug 21, 2018

My company purchased a vintage Otari MTR-90 MKII. It came without a power cord, so we had to rewire. It came with a 3-pin plug with a twist locking ring. The unit tag said it's 117V single phase. When lookling at the wires I notice they are Black, White, and Brown, not a color cose I'm familiar with. I looked in the Operational and Maintenance manual and in there the cabling is Black, White, GRN, so I'm assuming the Brown is the chassis ground and wire it this way. However it won't come up. Checking continuity to chassis, I see White and Brown are floating, but the black has .2 ohms to chassis. This is telling me Black is chassis ground. Anyone have an MTR-90 they can verify against? Any ideas?

Fred Thal · Aug 24, 2018

kfalls said:
I looked in the Operational and Maintenance manual and in there the cabling is Black, White, GRN . . .

Color coding a line cord assembly is one thing. What a manufacturer did inside their equipment is another. Further, vintage equipment is an unknown because there's no telling what someone may have done inside the machine. So I suggest that you first verify the primary power wiring from the locking power inlet all the way to the main transformer primary strapping.

Look at the drawing for the DS1Z power supply and observe that the main power switch (also a circuit breaker) is two-pole. If your power inlet has visibly numbered terminals, according to this drawing, terminal one would be the neutral, terminal three would be hot and terminal two would be the equipment grounding conductor. You could verify this with your ohmmeter.

I suggest that you also verify the transformer's primary strapping for 120 VAC mains connection, against this same reference drawing as well.

I'll ask a colleague this morning about a MTR 90 technical help mailing list. I imagine there is one somewhere. If so, I'll post that information here. I doubt that many pro multi-track tape machine technicians who work with MTR 90s are on audiophile forums.

kfalls · Aug 24, 2018

Fred Thal said:
Color coding a line cord assembly is one thing. What a manufacturer did inside their equipment is another. Further, vintage equipment is an unknown because there's no telling what someone may have done inside the machine. So I suggest that you first verify the primary power wiring from the locking power inlet all the way to the main transformer primary strapping.

Look at the drawing for the DS1Z power supply and observe that the main power switch (also a circuit breaker) is two-pole. If your power inlet has visibly numbered terminals, according to this drawing, terminal one would be the neutral, terminal three would be hot and terminal two would be the equipment grounding conductor. You could verify this with your ohmmeter.

I suggest that you also verify the transformer's primary strapping for 120 VAC mains connection, against this same reference drawing as well.

I'll ask a colleague this morning about a MTR 90 technical help mailing list. I imagine there is one somewhere. If so, I'll post that information here. I doubt that many pro multi-track tape machine technicians who work with MTR 90s are on audiophile forums.

Thanks for the reply. I was able to find a schematic for it online (along with about 100 other Otari tech dosuments). Running the line back from the AC input the black wire definitely goes to chassis, brown and white to the top of the power switch. Bottom line the unit is up and operational. Thanks for the comments and help.

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Problem with Otari MTR-90 MKII 2" 24ch Deck

kfalls

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Fred Thal

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kfalls

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