I'm not trying to build a power supply from scratch--just refurbish the one I have... 
(Topic ID: 158937)
Linked Games
Dyn O' Mite
Allied Leisure, 1975
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Berea, OH
Program resistor R1 is typically 120 ohms. The regulator develops a nominal reference voltage of 1.25V and impresses that across program resistor R1. There's some more involved equations on the datasheet, but I won't get into that. Here is an example of a 5VDC logic supply using fixed values for R1 and R2.
Quoted from ForceFlow:I'm not trying to build a power supply from scratch--just refurbish the one I have
You are really only adding a few more parts. not that big of a deal. the resistors can be tied directly to the chip legs.
Have you replaced the rectifier, and the filters yet? you will want to... and make that a full bridge rectifier, it will work better.
I know you did not want this thing to eat your lunch, but... while you are dining anyway... overhaul that power supply, and see if you can get the output correct, and stable.
you know, we are all pullin for you!
Quoted from Dr_of_Style:Have you replaced the rectifier, and the filters yet?
Yes.
Quoted from Dr_of_Style:I know you did not want this thing to eat your lunch, but... while you are dining anyway...
Believe me, I have already spent much more on this game than I could ever get back from selling it.
I'll try adding the resistors first, then a POT, and if that doesn't work, give up and go with a switched power supply to get 5v to see if that fixes the logic problems.
I already said earlier that I would have replaced the supply and have been done with it. But since you wanted to repair the original, why did you experiment with different regulators than what is in there, and not just replace it with a 78H05?
Everything looked properly hooked up but you are missing the two adjustment resistors -- R1 and R2 as in pix above.
Add them to the terminal strip shown in post #96, last photo.
1 -- diode you added is installed correctly - leave him. Should be there considering the 8000uF cap on output.
2 -- install R1 resistor between Vout to Vadj on the terminal strip -- white/blue (Vout) to red (Vadj).
3 -- disconnect incoming ground red wire from center tab -- install R2 resistor in series with incoming ground such that one end of R2 is grounded and other end of R2 is tied to center tab of terminal strip. (make sure you still have good ground to rest of boards).
4 -- make sure the heat sink isn't grounded or tied to anything else. Or make sure regulator is isolated from heat sink.
To do this cleanly - should be a 4-tab terminal strip... but that's nitpicking.
R1 - 120 ohm, R2 = 360 ohms.
Thanks for the instructions, Ed.
Well, it wasn't the results I was looking for but I wired everything up on a larger terminal strip. I got 4.13v on the boards at boot, but that slowly decreased and settled at 4.03v.
I was able to start a game, and switches responded and scored, even with the voltage that low.
So, what should I do to boost the voltage up to 5v where it should be?
20160519035432295_(resized).jpg20160519035424174_(resized).jpg20160519035452003_(resized).jpg
Quoted from wayout440:I already said earlier that I would have replaced the supply and have been done with it. But since you wanted to repair the original, why did you experiment with different regulators than what is in there, and not just replace it with a 78H05?
A 78H05 did not appear to be available from any of the usual places. And I thought the LM338K was a drop-in replacement with just a rearranged pin out.
Quoted from ForceFlow:A 78H05 did not appear to be available from any of the usual places. And I thought the LM338K was a drop-in replacement with just a rearranged pin out.
Unfortunately they are not available from usual places, they're out there on EBay.
Quoted from ForceFlow:what should I do to boost the voltage up to 5v where it should be?
R2 on the schematic, is that not a pot? I think that is where the adjustment comes from.
Quoted from Dr_of_Style:R2 on the schematic, is that not a pot? I think that is where the adjustment comes from.
Correct. Using a variable pot as in the example below will yield an adjustable DC power supply from around 2-30VDC.
LM338_basic_adjustable_power_supply_circuit_diagram_(resized).png
Quoted from wayout440:Correct. Using a variable pot as in the example below will yield an adjustable DC power supply from around 2-30VDC.
What POT should I use? I have 500ohm and 1k POTs on hand. I might also have one or two 2k or 2.2k POTs left over from another repair, but I'd have to check later.
Quoted from ForceFlow:What POT should I use? I have 500ohm and 1k POTs on hand. I might also have one or two 2k or 2.2k POTs left over from another repair, but I'd have to check later.
As a kludge since you don't have a 5k pot, you could take a 2K pot wired as a variable resistor with the wiper output going to a 2k2 resistor that then goes to the ground connection. You may have to experiment with the value of the resistor going to ground to find the sweet spot for voltage adjustment. Just don't tweak it with the boards connected obviously.
Or you could just go grab a 5k trimmer pot.
Quoted from ForceFlow:What POT should I use? I have 500ohm and 1k POTs on hand. I might also have one or two 2k or 2.2k POTs left over from another repair, but I'd have to check later.
The 1K POT would be ok, that's pretty much a standard value
Quoted from wayout440:The 1K POT would be ok, that's pretty much a standard value
Ok, I cut out R2 (360 ohm) resistor and replaced it with a 1k POT with the wiper leg going to ground.
Success--the 5v target has been achieved. A little kludgy looking and somewhat sensitive to fine-tune to the POT, but it seems to be working.
It looks like the POT is reading 160 ohm where I have it set for 5v. That being the case, if I use a 500ohm POT instead, would adjustments be less sensitive?
Now that I do have 5v, I just have to put things back together and do some testing for the game logic to see if raising the voltage has a positive effect, or if I have to go back to square one for troubleshooting the boards.
Thanks for helping me get this far guys 
I had the game on for over an hour, and the repeatable faults that were surfacing before did not surface. I still want to do more testing to be sure, but I'm hopeful so far.
However, a new issue cropped up while I was fiddling with things on the game at the show, but I thought it may have been connected to the other logic issues, so I didn't look into it very much. The tilt relay does not engage when a tilt switch is hit. I'll have to investigate that tomorrow. Could be anything--connectors, pins, the relay, driver board...
Quoted from ForceFlow:It looks like the POT is reading 160 ohm where I have it set for 5v.
Well that's certainly not what I would expect to see.
Regulated voltage=1.25((1)+(R2/R1)) Using your 160 ohm setting as a fixed value: 160/120 +1 X 1.25 = 2.91V
Same result with an online calculator http://diyaudioprojects.com/Technical/Voltage-Regulator/
Perhaps it's the caps playing havoc with the calculations? Most LM317/338K circuits use .1uf/1uf caps, not honking 8000uf caps. Oh well, it's working so I'd just as well leave it be.
*edit* ah, but I assume you probably took your measurement in circuit and that could be why you see 160 ohms, and thus the pot is not truly set at 160 ohms. Just a guess.
Quoted from wayout440:Oh well, it's working so I'd just as well leave it be.
*edit* ah, but I assume you probably took your measurement in circuit and that could be why you see 160 ohms, and thus the pot is not truly set at 160 ohms. Just a guess.
Yes, I measured while in-circuit.
Yeah, I don't think I'll fiddle with it any further if I don't need to.
if the reading was in circuit, I would be careful with claims.
but to answer your question, yup, a pot 1/2 the size, would have a longer swing and be less jumpy.
congrats on gettin it going!
1 week later
Quoted from ForceFlow:However, a new issue cropped up while I was fiddling with things on the game at the show, but I thought it may have been connected to the other logic issues, so I didn't look into it very much. The tilt relay does not engage when a tilt switch is hit. I'll have to investigate that tomorrow. Could be anything--connectors, pins, the relay, driver board...
Figured out the tilt issue. Pin 19 on the player up board wasn't actually making contact with the player up board. That pin leads to the driver relay board, which is why the tilt relay was not firing.
So, the game *finally* appears to be 100% operational. 
Toronto, ON
Quoted from wayout440:Congrats, now it's time to move to the next challenge.
Yes, it most certainly is. I've got plenty of other games crying for attention 
1 week later
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