Rockola 474, suddenly no sound

[jukerocks]

Rock 474 has long been reliable but quite suddenly produces no sound. It has the 48350-1A stereo Amp. Fuses are good, it's gett5 a measured 99VAC to one pin and -30-some VDC to another. Swapping themuterelay did no good, and the #3 micro tests good with clean connections. And yes, the speakers are plugged in and the volume control doesn't help. Any help as to where to start would be greatly appreciated.
Patrick

[jukeboxmarty]

Hi Patrick,

A good starting point is certainly checking various voltages in your amplifier.

You said, "it's gett5 a measured 99VAC to one pin and -30-some VDC to another".

I'm actually confused by that statement. Where did you measure 99VAC? What other voltages and at which locations did you measure?

And thanks.... but I wasn't going to ask whether or not your speakers were plugged in.

-Marty

[jukerocks]

Marty: thank you for looking at this. I have checked voltages at the plug on three units with identical mechanism: the 474, a 463, and a 464. At the 6-pin plug, all three measure about -35VDC at the top left, which appears to be purple/ green. But the AC voltages across the bottom are not good. The two working jukes measure 47VAC, 0, 47VAC across those pins. The 474 in question measures 100 VAC, orange wire , 58VAC, red wire, and 17VAC, orange / green wire.
It looks like I've got incorrect voltages that may have silenced the amp. Where to go from here?

[jukeboxmarty]

The AC voltages are obviously not correct.

The wire colors you specify are somewhat different from what my schematic indicates.

The AC wires coming from the power supply are indicated as orange-green (pin 5), red-yellow (pin 3) and orange (pin 1).

I'm assuming you measured with the (red) plug connected to the amp.

I would try disconnecting the plug from the amp, then measure between pins 1 and 3, and pins 3 and 5. The indicated measurement should be approximately 46VAC.

[jukerocks]

You've got me looking in the right direction. The voltages are way off, but reported correctly. Consulting the wiring diagram, the Orange on Pin 1 should show 46VAC but has 100VAC. The Orange / green on Pin 5 should have 46VAC but reads 17VAC. The Red / yellow on Pin 3 should go to ground but shows 58VAC. These measure the same at the plug with its ground pin as they do at the power supply and a common ground.

[jukeboxmarty]

Pin 3 gets grounded through the amplifier.

Did you take these measurements with the plug disconnected from the amp?

With the plug disconnected, did you measure between pins 1 and 3? and 3 and 5?

[jukerocks]

These are measured with the amp out, both at the amp cable plug and at the power supply at that cable. . But 1 to 3 and 5 to 3 both do read 46.7 VAC. Had not tried that. But the voltages of all three to common ground are way different than the other two machines. what might be going on here? Patrick

[jukeboxmarty]

Pin 3 is grounded to the AMPLIFIER once the red plug is connected.

Once the red plug is connected to the amplifier, you should get 0 volts across pin 3 and the AMPLIFIER ground. If you get ANY voltage, there is a connection problem between the plug and the amplifier.