Credit unit blows fuse

Hi Guys,

I'm revisiting this issue now, I may have mentioned it in a previous thread, but I think it warrants one of its own.

My Rockola 442 came to me with a 2amp fuse in the credit unit. The unit specifies a 1/4 amp slow blow... I changed it to the correct one, and every time I added a credit via the internal switch (or external....read on!), bang there goes the fuse.

The jukebox had its coin slot panel replaced at some point with an oversized panel featuring a "credit" button - Much to my annoyance! This was wired to the coin mechs coin switch. I'm aware now this is crappy practice at best, and have removed the said panel and wiring.

As advised by Ron I had a look at my coils in case the use of this button over the years had cooked them. All of the coils have a 470 ohm resistor wired in parralell to them. The bottom coil (connected to the credit switch on the credit unit), had a resistor that didnt look to healthy. I cut a lead to test it out of circuit with a multimeter, and it snapped right in half! So potentially this resistor has been damaged by this same issue. I replaced this resistor with a new one, but the problem still exists. I metered the coils (with resistors connected), and they all now read around 470-500 ohms. The bottom coil does read the lowest, but not by much. So I guess the coils are ok? The unit will also add and remove credit with no problems, providing a higher rated fuse is in place.

Is there anything else I should be looking at in the credit unit? I have been testing with all the coin mech parts disconnected so as not to confuse things. I can buy more coils, but not till pay day and only want to buy them if theres a fair chance this will resolve the issue. This has been an expensive project so far

Im presently using the unit with the 1/4 fuse and have put it to freeplay so I dont need to add credit. I've recently ressurected the original coin mech though, so am keen to start getting it ready for coin use!

Adam

Hi Adam,
Well, the credit unit does NOT "blow" the fuse ! What blows it is the credit switch(es). Switches are timed for individual coins by several factors, and if "off" in timing, this will cause the fuse to blow.
Factor #1 is speed at which the coin pass through the switch. #2 is switch "adjustment (gap)". 3. is Cleanliness of "slug rejector".
Factors 1 and 2, should be mentioned in your service manual, # 3 depends on you eyes (Hot soapy water--rinse well,dry TOTALLY, prior to using). Ron Rich

Hi Ron, I havent cleaned the coin switches yet, but I've not been testing with those, I've been using the switch on the front of the credit unit itself (the one underneath the metal lid). I've tried to flip this as quick as is possible, so I wouldnt expect this to blow a fuse? I assume this was there so engineers could test a jukebox when onsite without parting with their own money.

Though I guess cleaning this with switch cleaner also wouldnt hurt.

Hi Adam,
I don't recall ever seeing a free play switch under a "metal lid". I would ASSUME that it should be wired around the fuse, but I would need to confirm this on the schematic--If it's wired thru the fuse, and you don't "hold it", I would once again, ASSUME that the coin credit coil was degraded. Ron Rich

Yes thats right its wired around the fuse. When working (in this case with a higher specced fuse), it adds credits. I've tried to flip it as quickly as possible but it always blows the 0.25A fuse every time. I guess I should try replacing the coil and see what happens

Adam,
Now I'z confuzzed !! "Wired around the fuse"? If so, ANY size fuse won't blow, when using that switch ! And BTW, one should NEVER oversize any fuse, as for sure, you WILL destroy something !! That coil is degraded ! Ron Rich

Perhaps I havent explained this too well, I'll post some pics to show you what I mean. Or at least what I think I mean

Well I just replace all three coils in the accumulator unit and all three resistors....the unit still blows the fuse whenever credit is added. Is there anything else I should check? I'm using 250ma T fuses in the fuse holder. The cover states "1/4 amp slo blow", so this must be the right fuse?!

I would assume, if it is a "slow-blow" type,( on this side of the pond, it would be marked "MDL"or "313", if sloblo) it is the correct fuse--and I would assume that either your slug rejector is "dirty". mis-aligned, or one of Rob's Geppeto friends has "re-adjusted" the gap/pressure on the coin switches. All coins should fall through the coin switch VERY quickly, or the fuse should/will "blow".
Ron Rich

Adam: It looks like you're using the "service credit switch" to add credits. Some time back I posted a very similar problem with the fuse blowing whenever I'd add credits that way. See: viewtopic.php?f=3&t=5689&p=21932&hilit=460+credit#p21904 or easier yet search for "460 credit" and you'll be right there. My workaround was to either replace the momentary switch itself (which is not "momentary" enough) or just keep my hands off of it. It's either dirty or defective, but I decided to quit using it, since my kids like to drop half-dollars in it to play. I'm not sure if they even know it's real money, since we don't usually see that coin in use. If I'm servicing the juke and need to add credits, I tickle the coin switches. This adds multiple credits, but still runs the obvious risk of keeping one open too long and popping that fuse.
Patrick

Patrick,
"Tickling" the coin switches is NOT a good idea, on ANY brand jukebox--"coin switches" are designed only to work with coins, at a sustained pressure, and time, for each coin. The free play switch should operate a specific coin coil with no problems--but if wired thru the fuse, it must be "pushed and released" very quickly-- Ron Rich

Yes thats right its the service switch. I've cleaned it but always seems to blow the fuse no matter what I do with it.

Im wondering if these arent infact slow blow at all. I have some more coming and if I get the same issue I may just do as you say, or even try a 350ma fuse. My intention is to use coins long term so maybe I'll try the coin switches when I've cleaned them up

The larger size fuse is an even WORS-ER idea !!!!
NEVER over-fuse anything, as most circuits are fused at the maximum already --Ron Rich

I hear you Ron, and you're right to say that. I was wondering if modern slow blow fuses are any different in the way they work to older ones, so considered upping the rating a tad to see if any difference.

I have just tried a different brand of 250ma slow blow, and I cannot believe it, the problem is gone!!! Either the previous fuses I had were cheap crap from China, or they just behave differently. Strange, i never thought trying a different fuse would work! So far I've used the service credit switch several times and it adds credit just fine

I don't believe there are any "standard specs." for fuses--I think Bussman wrote some years ago and I thought that all (most?) other makers followed them.