Rowe AMI Cadette CMM1 restoration - help needed

[viperz]

It is going to be a long restoration with little time that I have to work on this jukebox nowadays. Pulled out the amplifier and volume control with its harness from the jukebox. Attached my bench speakers to it. Now I can properly diagnose it.

Problems:

1). Left channel is dead - very low output from preamp - will start diagnosing from here first.
2). Both speakers are humming quite noticeably (ground problem or ground loop somewhere - no wonder, there is a ton of ground points throughout the amp).
3). Right channel works, but goes into audible oscillation for first couple of seconds - could be oscillating at higher frequency after that for all I know...

Well, that's going to be bucket-full to work on in this amp...

[viperz]

Made some progress... right channel no longer oscillates - cleaned and washed all connections on preamp, replaced a couple of out of tolerance resistors. Left channel now works (replaced bad transistor), but.. output of left channel preamp output is now 1.5x higher than output of right channel preamp output... to be continued...

Oh, and the new belt is now in the mail... hopefully it will fit the changer.

[viperz]

Oh yeah, fixed the preamp - nice and even - output of left channel preamp was 1.5x higher than of right channel... On amp side, output of right channel amp was 2x higher than left... preamp output is great now on both sides... left channel amp - not so much, I blew out outputs on it... new outputs, 1 new driver and 1 new predriver... still doesn't fully work, but I am on it... and I found a failed pre-driver transistor that was causing low output of that amp board, but now need to fix my own booboo.. I was going to change all 4 outputs anyway, since the originals are rusted (although tested perfectly).

[viperz]

I can't figure this out... driver NPN transistor is blown.. metal round transistor marked "RCA 320C" on the top, driving 2N3055 output transistors. Rowe AMI p/n 701-00320. I can't find any cross-reference to this transistor

[Ron Rich]

Eugen,
Whatz the ROWE part # ? Ron Rich

[viperz]

Hi Ron,

Thank you for chiming in. I figured it out with some help from Facebook jukebox community.
I replaced both drivers with TIP29 and TIP30 matched transistors.
I also found one failed resistor - 2-watt 1K resistor - it was overheated in both channels, and cracked in "good" channel.

Now I got great even and balanced output from preamp inputs to each power output.

The only weird thing I have to figure out I'm this amp - for first one second after power up both channels do whooomp sound. Very quiet if no volume, or more loud if I have input signal.
I don't know if it is oscillation or just output coupling capacitors charging.

[Ron Rich]

Hi Eugen,
That's fairly normal for a jukebox solid state amp-- inrush current prior to the mute relay getting power to function -- Ron Rich

[viperz]

Thank you, Ron. Would that relay engage at the power up and only release when the stylus hits the record?

I still have to figure out the function of muting relay, or more what signal causes the relay to pick. On the bench obviously I don't have that connector connected. I will have to figure out amplitude and length of the signal in order to check if the relay operates properly. It looks like just a quick pulse to pick a coil, but I haven't checked that part yet.

[viperz]

Just a quick update. Got the bias current lowered in left channel to 100-110mA, still quite high, but should be ok. Bias in right channel is ~75mA. These carbon composition resistors drift really badly over time, and obviously move biasing points by a lot. Didn't help that I had to change 5 transistors in left channel along with 1 of 3 biasing diodes.
Either way, the amplifier seems to work on the bench well. Reassembled and reinstalled the amplifier, power distribution box, volume control and speakers back into the jukebox cabinet. Cleaned and oiled changer mechanism, installed new custom record magazine belt (fits perfectly!). The jukebox is definitely alive. Right now tonearm won't lift high enough to clear the gripper arm in horizontal position. I need to figure out if I put that mechanism together correctly, since it was in pieces, before I will follow service manual instructions and bend the tone arm rest bar upwards. Also, record magazine does not seem to be aligned with the gripper arm, will have to adjust that part after the tonearm lift fix.

I also finally was able to unlock and clean the coin box. Now it opens/closes and the lock works.

It also seems to be in free play mode since light "make any selection" lights up and I can make selections without dropping coins, but I'll figure this out in the future.

[Ron Rich]

Hi Eugen,
I think I would change any resistor that's "drifting", as once they start drifting, it has been my experience that they will continue to do so, on an almost daily bases. I am not familiar with the pricing unit used in that model, but if mechanical, and having dual "cancel (credit)" coils, the "normal way" these were jury-rigged, was to cut the connector in the center of the two coils, so that it was simple to re-connect the two wires--- Ron Rich

[viperz]

Ok, I keep working on the changer for now.

The record magazine is aligned with gripper arm, so I didn't have to adjust that.

I adjusted lead-in and cut-off positions, so stylus lands in first groove, and cut off switch works after last groove.

So still:

1). I don't understand why the arm doesn't rise high enough to clear the gripper arm.

2) The turntable plays at 33.3 (actually 34) rpm instead of 45 rpm. For some reason, it thinks I'm playing 33 LP, but my LP sensor is not even installed.

[viperz]

Got the speed issue figured out. I installed rubber motor mounts upside down. So playing 45 rpm now.

Now just need to figure out why the arm is not raising up.

Also need to adjust the tracking weight - the counterweight is pushed all the way in, so I can't reach the locknut, need some think pliers I guess.

And mechanical song indicator shows correct letters and numbers, but letters on middle roll are off to the side, can barely see the letter not sure how to adjust that yet.

[viperz]

Bent tonearm rest and the arm started going way up. I guess something was binding. Bent it back and now I can play both sides of all records just fine yay!

Now need to try to adjust tonearm tracking weight and song indicator wheels...
Then will move onto the payment mechanism, which is something totally new to me.

[viperz]

1). Tonearm tracking weight needs adjustment.
2). Annunciator letters - some come out perfect, some come out almost to the side of the display window.
3). Credit unit - adds credits fine, but does not subtract them, although I saw it subtracting once! I guess, signal doesn't get to cancel relay or cancel solenoid? Ron, I will look for the cut wire between coils, as you suggested, it is hard to see inside the credit union, even on the bench...
4). Credit unit related. I used to have 'choose any selection' light always on, now it stopped working, and I have no lights on. I setup the credit unit based on one of the selection options in the service manual I installed new light bulb. The 'any selection' bulb flickered a couple of times when wipers were moving along the credit unit circles. I washed all credit unit circles and bottom contacts with deoxit and a toothbrush. They were visibly oxidized and now they're quite shiny.


I added a few photos of counterweight and its locknut - not sure why I can't just turn counterweight by hand to move it outward? and photos of annunciator letters - C is perfect, J is almost sideways. 

[viperz]

Scratch #1, done. Some oil and I was able to move the weight. Settled around 3.5g. It was a bit over 5g in fully closed position.


The cancel solenoid is now firing. I guess, cleaning contacts worked. So now wipers go down all the way back, but I still can play songs after it's all the way back... What am I missing?

I have been reading and reading the manual on this credit assembly. It seems that for some reason relay K3 keeps the selector button-enabling solenoid engaged at all times, independent whether I have a credit or not... As soon as I switch the cycle/off/on switch to ON, I hear the solenoid behind buttons engaging.