AMI H Selenium Rectifier replacement

[greenmartian]

I am still working on the AMI H100 and am replacing the selenium rectifier (*F-5113) in the control box with a bridge rectifier.  It seems these rectifiers were slightly different in appearance on each of the AMI Models in the control box.  This selenium rectifier has two lateral 'wings' with terminal 'lugs' extending outward, and two middle 'lugs' joined by a solid wire. The two 'wing's' lugs bring AC power from the transformer to the rectifier and the middle 'lugs' take DC power to the capacitor. One of these joined 'lugs' leads from the rectifier to a resister and then to the capacitor. The other joined 'lug' goes directly to the capacitor. My bridge rectifier (BR) has only 2 of the 4 terminals identified. They are one AC and one + terminal.

Can someone clarify the terminal issues and answer a couple of questions for me so I can properly make this replacement?

First,
The labeled BR's AC terminal will receive one of the yellow AC power wires from the transformer. Does other yellow transformer wire go to the unmarked BR terminal diagonal to the labeled terminal?  
Is the last unmarked terminal on my BR, which is diagonal to the + terminal, if the AC terminal is diagonal, the - terminal?  If so, one or both of these terminals will deliver voltage to the capacitor either directly or through the resister. How do I determine which 'lug' should go to which wire to the capacitor?

Second,
Each wire leaving the middle 'lugs' of the selenium rectifier enters and leaves a small brass 'acorn shaped' structure (about 10mm in diameter and height) before continuing to the resister or capacitor. These are labeled "Sylvania SR 500". Am I correct in assuming these work to keep the current flowing in the forward direction only? If not please advise. Do I retain these in place during the replacement or does the new BR include this maintenance of current by design and they are not necessary?

Lastly,
These questions are important as I have been unable to locate an electrical schematic for this control board and it is none of the service manuals I can locate. Can you also advise me as to the proper voltages from the transformer to the rectifier and from the rectifier to the resistor and capacitor and from the capacitor to the receptacle F-880?

Any assistance greatly appreciated! Marty



  
  

 
 
 

[jukenorman]

Hi Marty,
In simple terms, you connect the two transformer leads to the AC tabs on the new bridge rectifier and connect the +ve tab to the capacitor. You leave the -ve tab on the bridge rectifier unconnected. That's because what you have is full wave rectification using a centre tapped transformer secondary, so only two diodes are required ie half the bridge rectifier. Does that clarify things?

I don't think I could answer your other questions without seeing your power supply. The output DC voltage from the silicon rectifier will be slightly higher than the selenium one.

Norman.

[greenmartian]

Hello Norman,

Thank you very much for your reply. Just to clarify, one the yellow wires from the transformer goes to the AC terminal as indicted on the BR and the other yellow wire goes to the terminal diagonal to the marked AC terminal as this is the second AC terminal. The marked + terminal on the BR, DC voltage, will be wired to the existing resister which then leads to the capacitor terminal. The BR terminal diagonal to the marked + BR terminal is the - terminal and will be unused. And, since the new BR contains internal diodes to monitor electric flow, the existing diodes, likely the brass Sylvania 'acorn' shaped objects wired between each AC wing of the selenium rectifier to each of its corresponding middle lugs, can be eliminated entirely with this exchange?

However, currently there are 2 wires coming from the DC terminal of the selenium rectifier. In addition to the wire to the resister/capacitor, a second wire goes from the same DC lug on the selenium rectifier directly to the same capacitor but a different lug of the capacitor. From the capacitor, this lug is then wired directly to the DC fuses within the control box. How do I account for this additional DC wire with the new BR?

Also, the DC wire, thru the resister and to the capacitor is then connected to the center pole of the capacitor to which also the Y/R wire from the transformer is connected and even a third wire which goes to the #3 slot of the 4-slot DC receptacle leading from the control box. I am sure my explanation is confusing, and I wish I could send you photos of Plates 6 and 7 from the AMI H100 service manual so you could better see the overall line schematics of this control box. Can I post or send photos through this forum?

Again...Many thanks!!!!
Marty

[greenmartian]

Norman... In re-reading my reply, I forgot to ask you about the values of the capacitor in this control box. The current capacitor has no markings to indicate its values and I am unable to locate a full wiring schematic with component and voltage numbers. Given this absence of component numerics, how do I identify the specific values of this capacitor so I can replace it at the same time?
Thanks,
Marty

[jukenorman]

Hi Marty,

First a clarification, the DC from the rectifier doesn't go through the resistor, the resistor is connected across the capacitor. The +ve from the rectifier, the capacitor +ve, the wire to the fuse are all the same terminal-wise so you can connect the wire to the fuse to the new silicon rectifier. I found the diagram of the AMi H power supply, that hopefully will make things clear. The capacitor is 1,000uF 50V.

best free image hosting

I should also have added that a fuse should be installed between the transformer secondary and the silicon rectifier to protect the transformer because silicon diodes are prone to go short circuit should they fail.

Norman.

[greenmartian]

Norman,
Please advise how I can attach a scan/photo to this message. According to the service manual and my actual visual observation of my Control Box, a current selenium rectifier DC line either goes to or comes from the resister and thus to or from the capacitor. Are you saying it is a return line back to the rectifier from the capacitor?

As I am sure you can tell, I am a complete novice at electronics. Detailed electric schematics are essential to my understanding of electric flow. In the only AMI schematic I can obtain, in addition to the straight line from the rectifier to the capacitor is the line to/from rectifier via to/from the resister to capacitor. No electric flow is indicated and no terminals on any component are labeled. Therefore, what you are telling me is that ONLY the line directly to the capacitor needs to be connected to the BR+ ? if so, what do I do with the rectifier-resister-capacitor line? There is also a current designated transformer fuse within the control box are you saying I need an additional fuse as well?

I apologize for being so ignorant in my understanding of electronics. It seems every time I think I understand how to read schematics I only find how truly little I actually do know. If you could visually see the limited schematic I am working with, AMI Service Manual H-338 Control Box "Plate 7", I am sure you could explain it to me so I could understand it.

Marty

[jukenorman]

Hi Marty,
Postimages is what I use to attach images, upload your picture and then copy the link for forums and post it in your message.

The rectifier converts AC to DC. Bear in mind that because it is a centre tapped transformer secondary, only half the bridge rectifier is used so the AC (two wires from the transformer) connect to the AC terminals. The DC negative which is at ground potential comes from the centre tap of the transformer secondary (simply because it is connected to ground) and that negative connects to the capacitor negative, the resistor negative side and the negative rail which goes out to the mechanism control circuitry on terminal 3 (see my attachment above). The DC positive connects to the positive of the capacitor and a DC fuse connecting to terminal 1, the positive end of the resistor and another DC fuse (different DC rail) connecting to terminal 2. All these DC +ve points are virtually the same terminal because they are connected together.

Does that clarify it? I had a look for "plate 7" but couldn't find it. I have a mish mash of manuals.

Norman.

[greenmartian]

Norman....test image of Plate #7

postimg.cc/jwK2LR82

[greenmartian]

Norman,
That is the image of Plate #7 I wanted to send you. The Y, yellow, wires from the transformer go to the 2 side 'wing lugs' of the selenium rectifier and the top central lugs are combined with a heavy wire with the right side 'lug', marked with a red dot on the actual rectifier, going directly to the capacitor and the left side 'lug' to the resister and then to the capacitor.

Thanks for the 'postimages' advice. It works very nicely!

Mostly...thank your for your patience. Using this schematic, can you explain to me again how I can wire the new BR into this unit?
Marty

[greenmartian]

Norman,
This is the actual photo of my control box with selenium rectifier.
postimg.cc/NydprzvP

[jukenorman]

Connect the two Y wires from the transformer to the AC terminals on the new rectifier. Connect the resistor and the 225 wire to the +ve terminal of the new rectifier. Connect the other end of the resistor, the R-Y wire from the transformer and the 230 wire to the negative terminal of the capacitor. Connect the other end of the 225 wire and the 229 wire to the positive terminal on the capacitor. Does that account for everything?

It would be a good idea to insulate the unused negative terminal on the new bridge rectifier and to fuse between the transformer and the rectifier.

As a matter of interest, was the selenium rectifier bad?

Norman.

PS If you copy the postimages hotlink for forums option, it should embed your image in your post.

[greenmartian]

Hi Norman.... Sorry for the delayed reply. I am a bit under the weather and not 'firing on all cylinders' the past few days. Thanks for the detailed information, that will certainly help me install the new BR. As for whether the selenium rectifier is bad, I think it must be. It shows no apparent signs of malfunction or damage and the transformer tests well, but I am getting only 19 v coming from the rectifier. It is my understanding the motors of the box need a minimum of 24 volts to run the mechanism. Am I correct in that understanding? If not please advise what I am missing or need to reconsider.

Many thanks for your expertise and willingness to help.
Marty

Also, does it matter which AC terminal the fuse is placed on to the BR?

[jukenorman]

I was going to say that it didn't matter which way round the transformer wires were connected but I thought how do you differentiate between two yellows? The reason is because the diodes only pass the positive half cycle. Yes 19V from the rectifier is low but have you checked the value of the 500 ohm resistor, if that has dropped in value it might be pulling down the voltage especially since it's rated at 10W!

Norman.

[greenmartian]

Hi Norman,

I am replacing both the ceramic resister, 50 ohm/10 watts, and the can capacitor, 1000 Mfd/50 v., as well as adding the new BR. If I am replacing the rectifier, I might as well do a general rebuild of the control box. None of the parts are expensive and locating a replacement amp was a far bigger challenge for this jukebox. Any additional thoughts or considerations would be greatly appreciated! They say there is nothing more dangerous than limited knowledge and understanding. That pretty much defines my electrical endeavors here.

Marty

[jukenorman]

The resistor is 500 ohms, not 50 ohms!

Norman.