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Pioneer M-90 Power Amp Voltage Selector Plug - HELP!

Marantz Man

Marantz Man

Mmmm, Rotel you say???
Hi Guys and Gals,

I have very recently aqcuired a M-90 power-amp in very good condition - however, the amp is the S/G model which is basically the dual selectable voltage (110/230v) model for the US service men when abroad. Anyway, my amp has lost the voltage selector plug at the back. I understand that this plug is also a fuse for the unit.

Does anyone have any info on this part, eg, part number, availability etc.

I have the Pioneer schematics for the US model and the European model but not for the dual voltage one.

Finally, does anyone have a spare 'plug/fuse' they could sell to me??

Any help would be greatly appreciated.

Thanks in advance.
Nick
 
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Right now I too have a good cosmetically M-90 KU on my bench. Just insides are fried out. As a result I am rebuilding it up totally from clean circuit boards.
Your voltage switch for S/G model is part number AKX-507. Usually the tab on the inner side breaks and the rotating part flies away from the body. I used to repair those switches by drilling and using a bolt with a washer to keep the rotating part affixed to the contact body.
You can make the amp usable for 120V by jumping contacts 3 to 6 and 1 to 4 (3-6 and 1-4) at the back of the switch. But Pioneer parts website still shows the part available for ~ 22 bucks. The AKX-507 went into pretty much all S/G, SD versions of amplifiers and big receivers of that era, such as A-91D, A-717, A-449, VSX-D1, VSX-9700 and others.
The fuses are located on a separate fuse assembly board. It is situated behind the rear panel to the right from speaker terminals if looking at the rear. There should be four slow blow fuses 4A each.
 
Me too. I had spent a fruitless hour searching to find the part number for the voltage selector. Learned a lot, but NOT that.
 
New schematics showed up on hifiengine, confirming everything including it's availability...

markthefixer said:
The voltage selector switch / fuse holder is the AKX-507.

You are in luck, later models used this part, and parts.pioneerelectronics.com lists them as IN STOCK for $22.25 (plus shipping and handling, which will bite).

The hifiengine.com site has schematics available for it, and they have a drawing showing the switch.

Best advice - buy the replacement switch / fuse assembly. Don't kludge it.
Click to expand...
 
markthefixer--thanks for the reply in the other thread!!

hennessy--does that pinout apply also to my A-77X? (For 120V that is)
contacts 3 to 6 and 1 to 4

I didn't see any numbered pins on the connector, but here is the wire color looking from OUTSIDE the amp...

Black .Green . Red . . (top 3)
Yellow Yellow Brown . (bottom 3)
Left . Center .Right

Any ideas which color to which color?

[edit] Looked up the schematic markthefixer directed me to, and it looks like it is black-to-green and yellow-to-brown if it IS like you say 3-to-6 and 1-to-4, looking from the OUTSIDE the amp.
Am I correct in looking at the pin numbers from the back (outside the amp)?

Also any warnings about looking into replacing the 28 yr old power caps, before throwing the switch?
They are Pioneer ACH107's @ 8200UF 63WV

I found this amp at a thrift store, so don't know the history. The heat sinks on the finals WOW'd me! They are HUGE!

Thanks, Brian
 
Last edited:
For A-77X the 1-4 and 3-6 for 120V stands correct.
I would hold myself from advising about wire colors. Might be a loud and costly mistake. Work from schematics on this one. Make pictures, use color markers, pencil, paper, and your brain.

Mark's advice about obtaining a new part from Pioneer is the best way, albeit expensive.

As of powering the unit for the first time the general idea is to use the Dim Bulb Tester. Saved my life many times. Have a ABC rated fire extinguisher nearby.
If there are no over current signs, no smoke, fire, explosions, etc., I would gradually increase the bulb power from 40 to 150 Watt and keep each bulb in the circuit for several minutes. Might help reform the capacitors if they are unused for a long period. For bigger amps I need 200W bulb, too. Be aware, sometimes a very low wattage bulb is not enough for protection/speaker relay engagement.
 
carnal said:
markthefixer--thanks for the reply in the other thread!!

hennessy--does that pinout apply also to my A-77X? (For 120V that is)
contacts 3 to 6 and 1 to 4

I didn't see any numbered pins on the connector, but here is the wire color looking from OUTSIDE the amp...

Black .Green . Red . . (top 3)
Yellow Yellow Brown . (bottom 3)
Left . Center .Right

Any ideas which color to which color?

[edit] Looked up the schematic markthefixer directed me to, and it looks like it is black-to-green and yellow-to-brown if it IS like you say 3-to-6 and 1-to-4, looking from the OUTSIDE the amp.
Am I correct in looking at the pin numbers from the back (outside the amp)?

Also any warnings about looking into replacing the 28 yr old power caps, before throwing the switch?
They are Pioneer ACH107's @ 8200UF 63WV

I found this amp at a thrift store, so don't know the history. The heat sinks on the finals WOW'd me! They are HUGE!

Thanks, Brian
Click to expand...

Get a VERY bright light, and carefully examine the back of the switch - there ARE numbers molded into the part by each connection. I hesitate to relay the sequence and position used by other parts numbers of similar ilk, as the consequences of their being different are so severe.
 
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