Help with power supply for jukebox

[jim43bob]

Hi, I'm a novice when it comes to electronics and am slowly learning. I have a power supply board that I cannot get the outputs that are supposed to be supplied. In the attached schematic you will see -13 vdc and -27 vdc output . Right now I'm getting - 15 vdc and -33 vdc and am allowed a maximum of 15.5 volt difference between the two. What I want to know is what I should be looking for that would correct this. After anyone looks at the schematic I will list what I have changed to try and correct the problem.
Many thanks in advanced
Jim

 

[73's de Edd]

Sir jim43bob . . . . .

This schematic and its tie ins to the left vaguely suggest of a Seeburg unit of the 50-60's with its Tormat memory core system for queuing the song selections to be played, after their entry.
Prior to its concept, they relied upon a massive double bar of small solenoids that moved a small magnetic "pin" to slide a brass square across a contact buss that started connection to make a scanning motor start transversing to find that pulled pin and stop the carriage mechanism at that point and then go into the record pull and play mode.
On the Tormat "electronics" it magnetized a small memory bead that then got scanned within the total group, upon finding that first "activated" core , the schematics top of the page silicon controlled switch . . .SCS3100 . . .triggered to brake the mechanism at the record . .ya da . . .yada . . .yada . . .

Now, can you confirm and supply the Juice Box's brand and model / series..

If Seeburg ,they usually are referred to as "B" "G" "J" " R" ,etc models.
Looks like your -13 volt supply is determined by the CR3110 Zener diode in the emitter circuit of Q3120, ant it just may be the permissible tolerance of the zener, creating the error on that supply.
Soooooooo . . . . . your expected -27, is being -33VDC.
The -27 is determined by the dump to ground by the . . .look to the left . . .terminal 12 connection of the emitter of the off board Q3113 getting to ground thru the R3189 and R3190 resistor path PLUS the R 3113's path to ground.
That last resistor R3113 is related to the -13 V supply which is within 2 V, so R3113 is being less suspect. More likely, it is an out of tolerance CR3110 zener, with them probably using . . . 10% . . . . . stock zeners. (Worse, if a " bean counter " was controlling parts purchases.)

So see how close R3189 and R3190 are now being, to their assigned resistance.

Also give feedback of the voltages being read across these regulatory zeners in their operation.

CR 3104
CR 3105
Plus conventional diode CR 3106.

CR 3107

CR 3110

CR 3115

Waiting for Brand and model / series.

73's de Edd
.....

 

[davenn]

Hi ya Jim
welcome to EP

In the attached schematic you will see -13 vdc and -27 vdc output . Right now I'm getting - 15 vdc and -33 vdc and am allowed a maximum of 15.5 volt difference between the two. What I want to know is what I should be looking for that would correct this.

Is it an older unit ... 25++ years ?

Well it's sort of an indication that transistor Q3120 isn't regulating properly.
But before replacing it, I would be replacing the electrolytic capacitors in that area

C3107 - 100uF, C3109 - 1000 uF, which are in the negative rails area

it probably wouldn't hurt to replace C3105 - 300 uF as well as it's negative side is involved in the supply

if this thing is really more than 20+ years old, then it's quite possible that the electro's are drying out and loosing value
and causing an increase of AC voltage on the DC lines which for general testing would just look like an increase in voltage on the rails
This could be confirmed but measuring AC voltages on those regulated DC rails the -13 and -27. You may find there's a couple of volts or so of AC



Dave

 

[jim43bob]

Hi 73's de Edd. Thanks for the quick reply. This board is out of a 1975 seeburg entertainer STD160 series DCC-4 (digital control center).Here is what I have changed so far on the board. All of the electrolytic capacitors as well as C3101 a mylar as reccommended on a jukebox site, I've removed all resistors on the board and changed all ( a total of seven) there were out by more than 5% excluding R3189 and R3190 which measured exactly 634 ohm and 750 ohm respectively. I changed all the zener diodes (3 @ 13v, 1@20v and [email protected] volt. I changed diodes CR3102,CR3103,CR3108 and CR3109 as sugested on the same site. I have changed Q3100 and Q3120 as well. I have cleaned the edge connector and all the fuse holders as well. I had checked all the new resistors I installed to ensure they were within tolerances.I'm just baffled as to what to check next! I have another identical board that when I install I get -13.5v and -27v which are damn near perfect.
Jim

 

[bushtech]

Get those voltages 73's de Edd asked for and publish them here. Then compare those voltages with the voltages you get on the working board.

 

[jim43bob]

Hi Everyone. I've attached a PDF of voltage readings at diodes requested. I added as well diode CR3112 because of the odd readings from the bad board. I have also added electrolytic cap C3108 only once again because of the odd readings of AC voltage on both sides of cap on the defective board. All other electrolytics only had ac voltage on one side and both good and bad boards were very similar voltage readings. I had already replaced C3108 on the bad board with a new one (as well as all other electrolytics) but that's not saying the new one is good either.
Many thanks
Jim

 

[73's de Edd]

Sir jim43bob . . . . .

Looks like you have two cumulative errors at fault in these two parts on the bad board.



73's de Edd
.....

[Mod Note -- Resized oversized image]

 

[jim43bob]

Hi 73's de Edd! I changed both diodes and it did the trick! Placed voltage differential within tolerances (14.3 volts) when allowed a max of 15.5. I can now make selections in the jukebox when before it would just scan twice which is a power supply problem. Did not even think of looking to check AC voltages for leaks, and even though I had changed all the zeners that doesn't necessarily mean the new one was within tolerances and that i shouldn't check all the diodes. I want to thank you and anyone else that chimed in. I'm one step closer in getting my juke up and running.
Jim