Rock Ola 460 amp blowing fuses

[rockolarick]

Hi again,

It seemed like I was happy on where I was at with fixing the jukebox, I thought I would do one last thing and try to clean/re-solder the wires on the gripper motor to try to get rid of a static it was making while in motion.  I took the motor in and they soldered it for me.  All was going good, put the motor back together, made a selection and as the gripper arm was setting the record down and the tone arm was moving towards the record, it started moving very slow and the mechanical fuse blew.  I pressed the red button and took the motor back apart as it was hard to manually turn.  Got it back together and all good there, tested it and worked again.  When it set the record down and started playing it, I then realized I have no sound.  I checked the two slo blo 3 amp fuses at the top of the amp and they were blown.  Went to the store to buy 2 more fuses, turned on the jukebox, heard a loud hum and both fuses blew again.  I am frustrated with myself because everything was working ok until I decided to open the gripper motor back up to try to get rid of the static when the gripper arm moves.

Where should I start with diagnosing this issue?  Since these fuses are blowing does that mean the issue is after the fuses in the amp? Would it be a good idea to start unplugging wires (output, preamp, driver board, etc) to see what board is causing the issue?

[Ron Rich]

Your amp needs to be serviced by someone familiar with it--do not replace the fuses till the problem is located and repaired, as you can cause further damage by ding so. Ron Rich

[rockolarick]

Thanks Ron, I am waiting to hear back from our local jukebox guy. While waiting today, I tinkered around some more and think there is an issue with the Amp transformer. I took my volt meter on both the amp and phono transformer. I was getting 25/35 VAC on the phono transformer, but was only getting .5 VAC on the 3 wires coming out of the the amp transformer. The schematic says there should be 46 VAC coming out for each wire.

Could this be the cause of the fuses breaking in the amp? Before I open the transformers, is there anything in there I need to be careful of? I am guessing this needs to be replaced and is not fixable.

[Ron Rich]

Can't tell you-- no schematic available here-- Ron Rich

[rockolarick]

Sorry about that. Here are the 2 pages of the schematic. The first one shows the amp transformer dropping it down to 46 VACs. If you follow that wire it will lead you to the power plug for the amp which the orange, orange/green wire saying it needs 46 vacs. If you continue on, that is where it goes into the two 3 amp fuses that keep blowing when the phono is powered on. this is on page 82 and page 3 of the manual.

postimg.cc/XpNPmggH

postimg.cc/9DDc52Bn

[Ron Rich]

What's the (ac)reading on the red/green & orange/green wires, with the fuses removed--power on ? Ron Rich

[rockolarick]

Both of these wires coming out of the phono transformer are reading 25 vacs each.

[Ron Rich]

Where are you reading--If reading each wire to ground, that's correct-- should read 50 volts from wire to wire. Ron Rich

[rockolarick]

I am getting 50 volts from those 2 wires. I did the same thing with the amp transformer, connecting the 2 red wires together and I get 92 volts and connecting the red to red/yellow, I am getting 45 volts. I didnt realize the red/yellow was a ground. I thought they were all positive leads.

Why was I getting 25 volts going from red/green wires when I was grounding one of the leads on the chassis, but getting .5 volts when I did the same thing on the 2 red wires on the amp transformer?

[Ron Rich]

Before you hurt yourself (or worse !), find info on how a transformer (should) work-- Be careful measuring voltages, if you don't understand what you should see !--it appears to me the transformer is fine. Ron Rich

[rockolarick]

Thanks for the info Ron. Sorry if I lead you down a rabbit hole. I will wait for the guy to call me back on servicing the amp.

[jukenorman]

Hi Rick,
There was a query raised on a 460 amp last July and there is a bit of information in that thread regarding supply voltages. It's always worth looking back previous threads, there is a lot of good info to be found! STFF - search the friendly forum!

Norman.