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Post by halfwaytree on Aug 14, 2023 12:25:07 GMT
My AMI J120 has a couple of issues with the pulse generator that keep ocurring.
The first is that when a selection is made when a record is already playing (ie the amp is not muted) the pulses from the generator are picked up by the phono lead and injected into the amp. This doesn't occur all the time and the resulting speaker movement is relatively small. However, what does occur all the time is a larger pulse when the pulse generator wiper comes to rest after a complete revolution. This occurs at the same time or perhaps just before the selector buttons are reset. This creates quite a loud pop through the speaker which I'm sure is not too healthy for it. I've tried re-routing the phono lead, but it makes no difference.
The second issue is that occasionally the pulse generator doesn't make a full revolution so the wiper never gets to its rest position. Therefore the selector buttons will not latch. I can sometimes coax the wiper into the correct rest position after closing one of the start relays. And then everything works fine again maybe for a couple of days or even weeks. However, there have been times when I've closed a starter relay and it still doesn't work, so I'm none the wiser of the cause of this. The erratic nature of the fault is making it difficult to pinpoint.
Any help would be appreciated.
Gordon
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Post by jukenorman on Aug 16, 2023 16:06:36 GMT
Hi Gordon, Are you sure that it's the pulses from the pulse generator that's causing the problem? I would have thought it more likely to be the relays in the pulse converter. You could make sure that the contact are clean etc and check (change if original?) any capacitors associated with these relays that are there for noise supression. The loud pop is likely the sprague relay operating. With regard to your second issue, do you mean that it's stopping in the home position and not advancing to the credit position? This came up very recently, check this thread. Norman. |
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Post by halfwaytree on Aug 21, 2023 13:16:15 GMT
Hi Norman,
thnks for your suggestions. The smaller pulses that I was experiencing seem to have disappeared so everything seems OK on that front.
As you suggested the large pulse is from the sprague relay as there is a spark from both front and rear relays on the right. The left side relay that has the capacitor does not spark. I recently replaced the two 100mf caps and the 0.1mf in the pulse convertor, and the 7nf cap (I think that is the value, IIRC) that is attached to left side front sprague relay. I also cleaned all the contact points in the pulse convertor and the sprague relay. The pop is still there unfortunately and it does seem to vary in intensity. The gap on the front right relay does look quite large so I'll see if I can measure it.
Regarding the pulse generator, yes, it was stopping in the home position and not advancing to the credit position. The jukebox is set to freeplay, but as this is my first AMI I'm not sure how that has been accomplished. The large multi-pin connector is connected to the credit switch box, but the small one is not. The wipers are very dirty in that box so I'll give them a clean and see if that helps.
Any insight on how freeplay is implemented on these machines would be useful.
many thanks
Gordon
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Post by jukenorman on Aug 21, 2023 14:06:23 GMT
You could try a capacitor across the contacts to see if that helps? A similar query came up on another forum recently and to quote verbatim "0.1uF 600V is a great noise reducer" so you could start with that value.
Freeplay on these AMi's is normally done by cutting one of the wires going to the coil of the subtract relay in the credit unit - so that it no longer removes credit when a selection is made.
Norman.
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Post by halfwaytree on Aug 22, 2023 15:33:28 GMT
Ok, thanks Norman. Just so I'm clear - I can see where the cap should be connected to the contact (contact 5 in the manual) does the other end go to the same connection on the coil as the existing .0047mf cap on contact 2?
thanks
Gordon
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Post by jukenorman on Aug 22, 2023 19:16:13 GMT
Hi Gordon,
Start with the contacts where you're seeing a spark and connect the capacitor across the two blades that are sparking (where the wires connect at the back of the switch).
Norman.
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Post by halfwaytree on Aug 23, 2023 18:51:59 GMT
Thanks Norman - worked a treat! The loud pop has gone completely 90% of the time and there is only the slighest of cone movement the other 10%. Nothing to be concerned about now. I did the front and rear switches on the right and as there were some free tags on the board that holds the 100mf caps I put the 0.1mf 630v caps on there and ran wires to the blades which was easier than trying to solder the caps directly to the blades - it looks neater, too.
Really appreciate your help on this,
Gordon
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