1975 Model 460 - Restoration in Progress Advice

[boogienights]

I am very excited to be a part of this forum and after recently purchasing the subject unit, I'm in the process of starting the restoration. Although I work on restoring old radios, this is my first attempt at at a jukebox.



I ran some basic checks starting with the power unit. The AC and DC voltages were all good within a volt or two. After watching some online videos, I went ahead and superficially cleaned anything I could see that needed it. Also, cleaned and reseated wiring connectors and relay contacts.



The unit powers up and the vinyl basket rotates with the select lever in scan mode. However, when in play mode, the 1st select button does not lock and no selection is made. The 'select any single' light is illuminated for credit. The write in arms does not energize or rotate and does not select a pin.



If I manually select a pin, the read out select arm operates, finds the pin, and the gripper arm loads the vinyl - the record plays and it is returned to the basket and then repeats with the same record as the pin is not being reset by the write in arm.



As an interesting observation. If I manually operate the lock bar solenoid in the push button selector assembly [it does not kick in automatically], button one will activate, and the read out selector arm will activate and rotate, and then stop at home position, but that's all.



Looking at the schematic, I'm suspicious of the selection control PC board and I did find R3 resistor had drifted way off spec as well as a couple of capacitors, I ordered new replacement electronics and will replace those soon.



In the same circuit board, I want to check the SCR's and am not sure of a reliable way of doing this. If anyone knows a reliable way to do this, please let me know and if they aren't good, what a suitable replacement may be?



Does this sound like I'm on the right track, or did I miss something? As a newbie, any advice would be very much appreciated.

[jukenorman]

No latching of the pushbuttons take place until the third digit. You should be able to follow the circuit for the first digit and why it's not registering from the schem-a-grams in the manual. It looks like you're nearly there though!

Norman.

[boogienights]

Thank you Norman. I'll take another look ab the schematic.

[jukenorman]

You have the description of the circuit for the first pushbutton press on page 19 and the schenatic with the "hot" circuits highlighted on page 18 of the manual - now that I've had time to have a quick look!

Norman.

[boogienights]

C1 is reading 0.096 [Spec 0.1] that one is good.
S11 has 0 resistance across the A to K and to G terminals in either polarity direction [same for S12, S13 and S14 - I think these are all bad and need to find a suitable replacement].
D1, D2, D3, D4, and D5 are passing current in one direction are good.
Q1 is good.
C6 reads 0.98 [spec 0.1] good.

If my SCR test is good [and I hope it is] all the other SCR's S1 through S10 show resistance A to K and to G unlike S12, S13, and S14. They all have the same part number except S14.

No guarantees those capacitors will be the same under load but I'll replace those anyway.

I have to check the hot circuit to C1 later, although the 'Select Any Single lamp is illuminated from credit switch contact #3. To be sure C1 gets power, I'll check that wire trace from the credit switch contact #4 to the board and report back.

Please Let me know your thoughts on my findings so far.

Ian.

[jukenorman]

The first digit is restricted to either a 1 or 2. Could this signal be getting lost? Have you tried both 1 and 2? I think it should also be possible to simulate this input at the circuit board.

Norman.

[boogienights]

Hello Norman. How would I go about simulating the input at the board?

[jukenorman]

If you look at the pages I referred to above, you will see that, for the first digit, the "1" pushbutton links R1 to R2 and should trigger the SCR S11. The "2" button should trigger S12 and links R1 to R4.

Norman.

[boogienights]

Ah, I see what you mean now. I'll do that. I can trace those.

[boogienights]

Hello Norman. Powered up the unit and with depressed pushbutton #1 reading zero power at S11 leg K or G with 13.24V at A. Same thing for button#2 at S13 with 13.79V at A.
Out of curiosity, I rechecked the 15 pin connector power supply and top row pin 4 from left -32.42VDC; bottom row pin 1 far left 35.2VDC; bottom row pin 4 from left 26.55 VAC.
All measurements taken with multimeter from source to ground.

[jukenorman]

Hi Ian,
I'm sorry I made a mistake in a previous post - the "2" button connects to S12. I have corrected the post now. I wanted to eliminate any likelihood of problems with the buttons which is why I was suggesting links at the board. If S11 isn't pulling in the relay K6 for "A" sides, then something is wrong in that circuit. Also the "2" pushbutton should trigger S12. You would think it less likely that S11 and S12 would both be defective so maybe C1 might be faulty?

The "3" button and upwards should trigger S13 and generate the "reset and reselect" light - does that work on the first digit? That's R1 to R14 but also relies on C1 not being defective.


Norman.

[boogienights]

Hi Norman, nothing happening with pushbutton #2 and S12 either. I will check C1 again and see what that's reading then look at #3 button and S13 with the "reset and reselect" light. I'll get a read out on those resistors as well.

[boogienights]

Hello Norman.  I worked through the selector unit circuit board last night and it is in sorry shape.  Out of 39 resistors, 7 were close to spec all others were off by a significant margin.  Most notable, 470Ω resistors R1: 855Ω, R3: 1125Ω, R18: 1316Ω.  This board needs a rebuild.  All capacitors will be replaced as well.  Based on your suggestion for replacement SCR's in the wanted parts add, some if not all of the SCR's will be replaced as well.  The diodes all checked out okay.  I'm thinking this board repair needs to be completed before any further troubleshooting.  Parts are on order.

[jukenorman]

That seems worse than I might have thought! I was reading back through your posts, it's quite simple to test an SCR with a multimeter on resistance - you should see high resistance anode to cathode in both directions. Then connect multimeter +ve to anode and gate and -ve to cathode and the SCR should conduct and resistance should go low.

Norman.

[boogienights]

Update from the weekend. I found a replacement selection unit circuit board and installed that and the buttons still did not work. However, I also replaced the credit unit and the buttons work now! I haven't tried the old board with the replacement credit unit in case that might cause another problem. So, it looks likely that both of those items were bad. I took more readings from the old and new boards and the old board is way different than the new one. I'll still rebuild that old one and keep as a back up. I haven't taken a close look at what may have failed in the selection unit. I'll do that next and see if that is easily remedied and keep that one as a back up as well.