Tempo 1475 - No Selections (Write in issue)

[bonnie59]

Hi There,
I have a restored 1475 that has recently developed a write in problem. No pins firing in any category.
I have replaced the large two part can capacitor in the credit unit and checked plugs, fuses, checked for stuck buttons but having no luck.
Reviewing the schematic and wondering what to try next. . .
Is anyone out there able to offer any suggestions to try?
Many Thanks & Kind Regards
Dan

[jukenorman]

Hi Dan,
First up, do you have credit? Next, is there DC voltage at the capacitors you replaced? In January you started a similar thread - most of what was said then would still apply now.

Norman.

[bonnie59]

Hi There,
Thanks for the response Norman.
Yes definitely have credit. The select light is lit and when I make a selection I get the "click" and the carousel starts scanning. Also when the correct number of credits are used the select light goes out and I cannot make anymore selections. . . . It just never finds a pin to select and play, and instead just completes two laps and then stops.The capacitor I replaced is the was the 300/150 large capacitor that lives inside the credit unit.(definitely wired the correct way around and in fact has sorted out my credit accumulation issues).Looking at the schematic it's the 300mf / 50v side that via the number button bank fires the rest coil and the 150mf / 50V side is credit accumulation.
As the credits are reducing with each selection OK the reset coil must be being pulled in Ok and hence the 300mf side of the capacaitor must be getting charged up OK . . ? By my understanding the other switches connected to the reset relay are what power the commoning relays, sector coils and scan control unit. Again the scan control unit kicks in also showing that the 300mf is doing its job.

[jukenorman]

Hi Dan,
No, that is not correct. The scan control relay is AC operated. When the 1 to 40 buttons are in the relaxed position, a circuit is made through all the buttons to charge the 300uF capacitor. When a button is pressed, the charge in the capacitor is then routed through that button to the selector coil (simplified quite a bit!). I think you need to start with the 300uF capacitor - is it charging?

Norman.

[bonnie59]

Hi Norman,
Thanks for the understanding and help, forgive me I am new to this, but am doing my best to learn.
So to check, I have powered up the juke and then powered down. I then removed the plug from the front of the credit unit and checked the voltage between pin 6 (Gy-Bk) 300uf and pin 4 (Bk) ground. Directly after powering down I am seeing around 33V (this does slowly drop)
This suggests that the cap is charging, albeit not to 50v or is it to be expected that by the time I power down and remove the plug it will have dropped?
Next stop from here is the button bank, so i guess I should be checking to see if I'm seeing the 33V at the common rail on the button bank.

[jukenorman]

Hi Dan,
It was time for me to pull out the manual and I can see that my memory has failed me a bit and I have misled you! The 300uF capacitor is in the circuit that pulls in the reset relay and that must be happening because the scan control relay is coming in. Incidentally 33V is probably as much as you would expect to see on the capacitor. The 300uF capacitor is important because its charge determines the length of pulse going to the selector coils due to the time that the reset relay is held after a selector button is pressed.

Next step is to clean the contacts on the reset relay. The reset relay is marked as Item J on the accumulator assembly in the manual. There are three contacts - one pulls in the scan control solenoid, a second routes power to the commoning relays and the third to the selector coils. There is a "sticky" on contact cleaning to refer to.

Norman.

[bonnie59]

Thanks Norman,
Contacts cleaned, but no improvement. Another symptom that I have which I wasn't sure was related is that when I press a selection the scan start solenoid fires, but 9/10 it doesn't engage the ratchet and start the carousel scanning. I have to fire in a number of selection in succession and then eventually it engages and the carousel starts to scan. I put it down to a worn slot in the ratchet where the solenoid arm joins the ratchet. Looking closer at the selection pins as I'making a selection you sometimes see the pin quiver but rarely. Given the solenoid is struggling to engage the ratchet and the pins are struggling to fire it's almost like both are struggling for voltage??
Come to think of it, the gripper motor seems to be running slower that it has done too.

[Ron Rich]

Hi Bonnie,
It would be my GUESS, that the scan control and the pins are 25 VAC, both fired from the pricing unit, with the subtract pulse. I would check for a "pitted/burned" contact there-- If you don't know how to "clean contacts", see the FAQ's page for help--do NOT "spray them with contact cleaner" !
Ron Rich

[jukenorman]

Hi Dan,
Yes, I think that the scan control solenoid not pulling in regularly is significant - it is operated by the reset relay. If you are not getting a solid pulse on the reset relay, it takes us back to the 300uF capacitor and its discharge. The No. 1 button is closest to the capacitor so it has the best chance of firing (the others go through a series link of closed contacts). Since you've replaced the capacitor and we seem to have ascertained that the capacitor is being charged, it's pointing to contact problems on the button bank. You need to have a good solid "fat" pulse to the reset relay - that is crucial to making selections.

Norman.

[bonnie59]

Thanks Ron Rich and Norman,
I am going to give the contacts a more thorough clean in line with your guide Ron before diving deeper towards the button bank.
My initial clean was with a solvent, but looking more closely they may be burnt a little.
I am really struggling to find a burnishing tool here in the UK. What could I use instead do you think? I'm thinking very fine wet and dry paper maybe? 2000 grit wrapped around a wooden stick?
Do you disassemble the contacts to clean or in situ?
Kind Regards
Bonnie

[jukenorman]

Hi Dan,
I should also have mentioned that the plugs/sockets can also be a source of problems - there is a 40 way Jones plug from the button bank for example. I would absolutely avoid a burnishing tool on that type of contact. I remove the button bank and wash it with a water based janitorial cleaner - the sort of thing used to clean office toilets, then rinse it and let it dry. Any delicate items like solenoids should either be removed or protected.

Norman.

[bonnie59]

Hi Norman,
Noted, thanks.
I am talking about the 3 contacts in the Credit unit actuated by the reset relay. According to the contact cleaning guide these can be cleaned using a file and then burnished?
Kind Regards
Dan

[Ron Rich]

Hi Dan,
"Filing" them does NOT "clean them" ! It removes silver. One should avoid filing unless necessary to remove "pits/burrs". "Sandpaper" of any kind is a No-No, in my book, as the sand always embeds itself into the silver--- If you can't find a burnishing tool, I understand there is some sort of "stick" used in the UK --Never have seen it, nor used it-- I do most contacts right where they are--no dis-assembly unless badly burned-- Ron Rich

[jukenorman]

Hi Dan,
Yes I thought you were threatening to attack the button bank switches with a burnishing tool! You can get burnishing tools at Mouser - mouser.co.uk. I have never bought anything there so I don't know what their delivery charges might be - it's only fairly recently I discovered that they operate in the UK!

Norman.

[bonnie59]

Thanks for your guidance on this.
Currently awaiting a Mouser delivery with a set of 3 contact burnishing tools.
Once I receive them and have properly cleaned and burnished the contacts I will see how it performs and let you know.