Techna 480 Power Problem

[craigf451]

Context: Techna 480, fully cycles, selects record accurately, plays record, puts it up, selects another, plays, etc. resets when selection series is over.  It appears to work as it should.

Issue noted: During Sequence 16, music cycle starts, the latch relay buzzes. It is supposed to be in the reset coil position as the music plays.

I've discovered that I'm not getting 32V at the mechanism board ( measure 19.78VDC going into latch relay from CR307 and ~21.8VDC going into R311 and E of Q305) and I've traced that back to the power regulator.  I've got the parts and service manuals; however, there are not full voltage marked schematics to determine where an issue might be pinpointed.

I've verified all resistor values on the regulator PC Board Assembly and Power PC Board Assembly, replaced the few electrolytic capacitors on each of those boards, and retouched all solder joints on the boards.

Pin voltages on the Regulator Board that I think impact the Power PC Board are Pin 9 = 26.76VAC as input, which seems to track to what spec is for the winding #3, and Pin 13 = 21.88VDC, which should end up at 32VDC.  

Pin voltages on the Rectifier Board from the Transformer (All AC) 1) 9.2  2) 7.28 3) 0  4) 15.46  5) 14.13  6)  6.55

Things in the path on the Regulator board I suspect but haven't checked are the Q201 Darlington and the CR201 & CR202.  

Any ideas or alternative causes for the relay buzz.  Follow on steps work in the sequence and it is not intermittent.

Thanks,

Craig F.




  

[jukenorman]

Hi Craig,
Do you have the large fold out schematic that originally came with the service manual? That would give a full circuit of the regulator board for example. Does the 32V come up if you pull the relay (is the relay the problem?)?

Norman.

[craigf451]

That type of schematic is not present in the 2 books I purchased from the recommend source.  A picture of the board layout and parts list is available but no markings of voltage outputs is on that picture.

The regulator board and transformer output pin voltages noted in my post were taken from the power supply disconnected from the jukebox and corroborated reg board measurements taken while everything was hooked up. Relay in or out didn't matter on the supply voltage measurement.  Doesn't disprove that the relay may be bad.

I'm kind of curious as to why the rest of the cycle works at 10V lower, too.  and it dawned on me this morning that both latching and reverse relays are 24V relays.  So, I shouldn't expect 32V into the relay, but seems like a little more would stop the buzz?  or the relay is bad.  Anybody got a part number?

Second curiousity then pops up.  The magazine and gripper motors should be running on 32V, if I read the sequence schematic correctly.  Everything seems to be working. I guess it is just running a bit slower, but with enough voltage to trigger all the other cycles.

Craig F.

[Ron Rich]

Craig,

There is another RockOla 480 post below--with "end of record" problems-- check it out--

If you purchased that info, and did not get the schematics, but paid for them( you axked, as it says to do ?)--- scream-- at that source !!! Ron Rich

[craigf451]

Much appreciated.  That appears to be the exact issue I'm having.  I'd read through that prior to having this issue, did not connect the dots, and did not re-read.

I will follow through with that trail of thought.

Craig F.

[Ron Rich]

Craig,
Good luck ! Ron Rich

[craigf451]

Success! Replaced both caps, now there is proper power, no buzzing, and quicker cycles, too.

Craig

[Ron Rich]

Hi Craig,
KooL--Enjoy your music ! Ron Rich