High Voltage not high enough

[Neverending Project]

My displays on my Stern Flight 2000 are not lighting. It is most likely because the regulated HV test point is only reading 145V, and it should be >155V. The problem is that I can't adjust it with the variable 25K-Ohm resistor - it doesn't do anything.

I have rebuilt the entire voltage regulator, and all the test points look good without any load (connectors J1 and J3 removed). When I then connect J1 and J3 to the regulator, and remove all but J3 and J4 from the SDU-100, the HV at TP2 only reads 145V. The unregulated HV at TP4 reads about 260V. But turning the variable resistor at RT1 has no effect. I know the resistor is fine because it is brand new, and I can probe the solder points on the back and see the change in resistance as I turn the screw.

I have also rebuilt the entire 5V and HV sections of the SDU, replacing just about every part on there (including the filter caps and Q21 and Q23). Any thoughts on where to trouble-shoot?

Thanks.

[ChadTower]

Did you rebuild the connectors?  Something is resisting more than it should or leaking to where it shouldn't... but since you rebuilt everything odds are that you've got an over resistance in that circuit.  Best guess is the connectors.

[Neverending Project]

I replaced the header pins on both the regulator and the SDU, and the connector on the regulator. I suppose I can replace the connector to the SDU also (it is not brown or burned at all), but if there is extra resistance somewhere, shouldn't changing the variable pot still change the HV at the test point, even if it is low overall?

[ChadTower]

I replaced the header pins on both the regulator and the SDU, and the connector on the regulator. I suppose I can replace the connector to the SDU also (it is not brown or burned at all), but if there is extra resistance somewhere, shouldn't changing the variable pot still change the HV at the test point, even if it is low overall?

It probably should, yeah, but without looking at the circuit I don't think I can give you a guess as to what would be causing that.  Are you sure they're on the same circuit?

[StephenH]

This might help you:

http://www.pinrepair.com/bally/index3.htm#display

[Neverending Project]

I am beginning to wonder if it might be the rectifier that has a problem. According to marvin3m, the rectifier should show 150V at its TP2 with connector J3 removed, and 230V with it attached. I am seeing 185V and 260V respectively. So I wonder if this extra 30V it causing the problem with the HV not being regulated correctly.

But I did completely rebuild the rectifier too. Hmm, I suppose there is the possibility that I could have botched something in my repair job... OK, maybe I will pull the rectifier again and take a closer look at all the components I replaced.

[ChadTower]

Did you test the recitifier out of circuit?  It's easy - it is four diodes. 

[Neverending Project]

To answer your question: no. But all three rectifiers on the power-supply board are brand new. And I used 200V 35A replacements, so they should be good-to-go.

But I was just reviewing the site where I bought the power-supply rebuilt kit (bigdaddy-enterprises.com), and saw that the kit included four 1N4004 diodes. According to Clay, these are used for the 170V for the score displays. He (Clay) says to replace the stock 1N4004 with 1N4007 or better. Do you think this might be the issue?

Oh, and of the other three bridge rectifiers I just found out they aren't for the HV circuit: BR1 is used to convert 7.8 VAC to 5.5 VDC, BR2 converts 12 VAC to 11-16 VDC, and BR3 converts 49 VAC to 43 VDC. So they shouldn't affect the HV at all. But now those 1N4004 look suspicious to me...

Update: Nah, from what I can tell, the only difference between the 4004 and 4007 is that the 4004 have a 400V peak reverse votlage, and the 4007 have a 1000V peak reverse voltage. Both should be good for this application.

[ChadTower]

Yeah, Clay's guide frequently suggests upgrades on parts like that.  So many people use it that I consider it vetted and trustworthy as far as replacement parts go.

[Neverending Project]

OK, I am trying to narrow this down to where the problem might be. With only J2 connected (no backbox connections) the power supply board should show 150VDC at TP2 (according to Clay's info), and it is showing 190VDC. It seems like there is a problem with my power supply board, but if my voltage is too high, shouldn't the regulated voltage also be too high?

Also, according to the schematic the transformer should be sending 173VAC to the rectifier circuit:

But with no load I am seeing 190VAC on the transformer terminals. Should I suspect my transformer has a problem?

[Blanka]

It's quite normal that a unloaded transformer gives higher figures than a loaded one. 190V AC sounds Ok for an 173V unloaded trafo.

[ChadTower]

Plus the transformers themselves almost never die.  Those things are heavy duty.

[Neverending Project]

OK, next thought. I checked all four diodes on the board and they all test good (and they are all new), and I didn't find any shorts either. Even though the voltage at the test point seems to be out, should I focus my troubleshooting on the SDU, since I can't imagine what else could be wrong with four simple diodes?

Or I could try to find a replacement power supply board to test it in place, so I can rule out the board as a problem. What would you guys do next?

[ChadTower]

I'd probably bring the displays to a good machine and make sure they are still good.

[Neverending Project]

I'd probably bring the displays to a good machine and make sure they are still good.

Since none at all are working, and the trim pot does nothing to adjust the HV, and the test point is too low, I am going to try to get the HV fixed first. If I get the HV in range and they still don't display, I will see if I can figure out a way to test the displays (I don't have any good machines to test them on).

I have been pouring over these boards, trying to see if I installed any parts wrong or shorted anything. I cut out a 100K resistor on the SDU thinking it was bad (it didn't test in range on the multimeter), but it turns out it was across the filter cap, so the multimeter couldn't test it in circuit. So that wasn't the problem. I checked all the other resistors and they are fine.

So if there is a problem on the SDU, it would either be with the zener diode at the center tap of the trim pot VR1 (new), or maybe I shorted the one of the leads of Q21. I am going to replace the diode and resistor I clipped and see if that does anything.

[Neverending Project]

I thought I might have installed the wrong part at VR1, but I just double checked and the markings that I didn't recognize were because it is an equivalent 2EZ140. And it tests fine on the board.

So I'm still baffled here. I am tempted to go ahead and replace the voltage regulator board just to be sure, but my brain keeps asking me what could possibly be wrong with four simple diodes? But if I do get a replacement board from pin-logic, I can also pick up a replacement HV circuit for $35 - cheaper than a new SDU board.

Hrm, $68 plus shipping shipped for the peace of mind to know that the regulator board works perfectly is tempting. Why do I always over think things?

Edit: That $68 includes shipping... I just got pushed closer to the buy-now side.

[Neverending Project]

I replaced the HV section of the SDU with the HI-Volt board from pin-logic.com. The replacement was as easy as removing the 20 or so parts from the board that make up the HV circuit and then soldering four wires into some existing holes. It was really straight forward.

So now the scores do display, but they are flickering quite a bit and some of the digits are out. At least I know there was something wrong with the HV section of my SDU board. Now that is fixed so I can move on to trouble-shooting the flicker and blank digits. I'll have to check, but I think the same digits are out on all displays. That should be a clue.

On a side note, the entire pin-logic experience was amazing. He answered my e-mails within minutes, and the very moment Paypal notified him of my payment the board was in the mail. I placed my initial order on Thursday night at 9:00PM Pacific and received the boards on Tuesday afternoon. Superb!

[Neverending Project]

Sounds like you've got a set of nearly dead displays... you're never really going to know until you test them in another game.

I haven't looked into it at all, but does it need to be a Stern (or Bally) that I test them in? I could try them in a Game Plan Pinball Lizard, at some point, since that is at my Dads.

[Neverending Project]

There was something wrong with the HV circuitry that needed fixing. The displays went from completely off with no orange glow in the corner to working, but flickering. The HV went from out of range to in-range. And if the same digit is out on every display, then that tells me there is something wrong with a connector pin or header.

The displays may also be dead, but the replacement parts were needed anyway.

[GPE]

I replaced the HV section of the SDU with the HI-Volt board from pin-logic.com. The replacement was as easy as removing the 20 or so parts from the board that make up the HV circuit and then soldering four wires into some existing holes. It was really straight forward.

So now the scores do display, but they are flickering quite a bit and some of the digits are out. At least I know there was something wrong with the HV section of my SDU board. Now that is fixed so I can move on to trouble-shooting the flicker and blank digits. I'll have to check, but I think the same digits are out on all displays. That should be a clue.

On a side note, the entire pin-logic experience was amazing. He answered my e-mails within minutes, and the very moment Paypal notified him of my payment the board was in the mail. I placed my initial order on Thursday night at 9:00PM Pacific and received the boards on Tuesday afternoon. Superb!

Response to an old thread... but -- I'm curious.  Has ANYBODY else other than me ever looked at what parts are actually used on this replacement board?!?!?
The parts used on this board exceed the manufacturer's ABSOLUTE MAXIMUM ratings by more than 2x!!!
What would possess somebody to market such an item?
Sure, these will work for awhile but there is no way these will last in the long run.

 

Ed
 

[GPE]

Isn't he the guy that bought a Pinball Lizard board, copied it exactly, and ran off cheap copies after hours at his job? 

That's the story I heard and I've seen the products side by side and it sure sounded convincing.

I don't know - I've never seen a PBLiz board of this type.  But I wouldn't doubt it if the design was copied.

I do know the board mentioned above uses the Texas Instruments TL783 as the regulator.  This part has an absolute maximum Vin to Vout differential of 100 volts.  This one has a differential of about 230 volts - more than 2x.  Some will argue that the differential is actually about 60 volts (Vin of 230 minus Vout of 170).  BUT Texas Instruments warns (in several places) that Vout MUST account for two conditions: 1 - shorted output, 2 - turnon conditions when briefly Vin = 230 and Vout = 0.  I showed this design to one of the Texas Instruments linear FAE's -- they laughed and just said 'good luck'.

Ed