Rockola 478 Mech Power Board Problem

[Keith Gorham]

Feb 13, 2021 22:29:27 GMT jukenorman said:

I cannot identify the red button on the schematic - can you be more specific? And after you press this red button and you have 24V on the relay, does it pull in?
Norman.

The red button I refer to is the clear button on the logic board.  On the schematic, it is just to the right and down from the mech controller IC.

[jukenorman]

OK Keith, I have found the red button. I don't think it has much relevance to your problem except that by doing a "reset", it is giving us some good info!

So we are back to the point at which you push the button and the voltage at pin 3 goes to 25V and pin 1 goes to 0V - does the reset coil energise? If not, you need to check R309 etc as I previously indicated.

Norman.

[Keith Gorham]

Update again. First I want to thank everyone that has attempted to help me fix this jukebox and I feel I have provided miss-information and for that I am sorry.

The reason the gripper motor continues to turn is that the latch coil is getting both signals at the same time and as an result it does not reset to allow the gripper motor stop.

The latch circuit should have been disabled in sequence 14 Step 3. The micro switch #1 should send 32 volts to the logic board then send an signal back to the mech. power board to disable the latch circuit. I attempted to trace the signal but got to the point that I was not sure what was going on, and my significant other got tired of pressing and releasing the switch.

[jukenorman]

Hi Keith,
So is it the case that at the end of the cycle (when the gripper is parked over the carousel) and you manually flip the relay into the reset position, that the latch relay will energise in sequence 14? Or maybe you don't have to flip it if the reset relay energises when the red button is pushed when the gripper motor fails to stop after transfer?
Norman.

[Keith Gorham]

I think I found the problem. I traced the circuit to the hex inverter. Pin 1 input was low as was pin 2 the output. The low input was correct, and the output should be high. When I applied high to the output pin, the gripper motor stopped. I pulled the chip and bench tested to confirm that one inverter was bad, but the others seemed to work ok. I am glad they used off-the-shelf components as that inverter is available on eBay for about $5. I will know for sure in about an week. Wonder if that is something that radio shack would have stocked back in the day....

[jukenorman]

Hi Keith,
No "think", you have found the problem! If the hex inverter gate is faulty, it won't allow the latch coil to relax when it should! So the reset coil subsequently cannot overcome an energised latch.
Norman.

[Ron Rich]

It's probably something RS SHOULD have stocked--they may have saved the company by stocking what was needed, but they chose to stock/sell that crappy "RCA" (made in China)branded, stuff instead. Ron Rich

[Keith Gorham]

The chip did fix the problem, but having a minor issue as it does not want to grab the record after playing. The part opposite the record does not go into the center piece far enough to grab the record. If I put my finger on and apply a little pressure it will grab the record. The part I am talking about is the piece that goes underneath the center mechanism.

[Ron Rich]

Didja READ the "STICKIES" ?? Do it and you question will be answered ! Ron Rich

[Keith Gorham]

If you are talking about cleaning and using the correct oil on the mechanism, then yes I have.

I guess I could have explained that I was concerned that I may have the teeth on the gears not installed correctly, but the more I exercise the mechanism, the better it is getting.

Question, should this machine allow the user to select an record that does exist in the machine, and then thee machine attempt to pull an record that does not exist and place it on the turntable?

Thanks!

[Ron Rich]

Did you bother to READ the sticky on the gripper above ? Phono has no idea if there is a record in a slot, or not Ron Rich

[jukenorman]

It's a 160 select, there are no spare slots that I am aware of. You can only select 1 or 2 for the first digit, all ten buttons for the second and eight buttons for the third digit - so you cannot choose a rogue selection. That is covered in the manual.

Norman.

[Keith Gorham]

Sorry, I am asking questions that are apparently addressed elsewhere. I have tried to search prior to asking.

[Ron Rich]

Don't need to search-- just read your "messages".
Ron Rich