(Topic ID: 298748)

EBD 43V at TP3 (should be 11.9V) - transformer issue?!

By m4tt

65 days ago


Topic Heartbeat

Topic Stats

  • 12 posts
  • 6 Pinsiders participating
  • Latest reply 60 days ago by Quench
  • Topic is favorited by 1 Pinsider

You

Linked Games

Topic Gallery

View topic image gallery

2021-08-18 13.23.36 (resized).jpg
EBD power (resized).png

#1 65 days ago

Hi all, I've searched for anyone having a similar issue but no luck, so hoping someone can shed some light.

I've got an Eight Ball Deluxe Limited Edition that was working fine for months. Then had a display issue which led me to start checking voltages back through the Solenoid Driver Board and then back to the Power Rectifier Board. I sorted the display but had found that TP3 on the rectifier board was reading 15.9V when it should be 11.9V. The game was running, so although I had a bad feeling (TM), I played on.

Then fast forward to a few weeks ago and the game wouldn't boot. The MPU doesn't reset, so I get no flicker and no flashes. I've probably got another issue there now, but that's for another time. I checked the voltages again and found 48V at TP3! I've added the wiring schematic picture to this post for your reference. My immediate thought was that there must be something wrong with the diodes CR5, 6, 7, 8, but if you look, they're fed with the two blue wires from the transformer and get only 14.2V. So then I thought it must be a short and I went over the board time and time again, everything was as it should be. So I started taking components off like the BR2 Bridge Rectifier which feeds the TP5 which should be 43V, as the similar voltages seemed to point to that. Anyway, went down a rabbit hole there with pretty much everything off the board, fuses out and still getting weird voltages where they shouldn't be...

Fast forward a couple of weeks and I picked up a Centaur 2 - same cabinet and same power rectifier board (well the EBD has the rev B but they're basically the same?). So I checked all the test points in the Centaur and they're all perfect (so it's not my multi-meter) then I pull out the board and put it into the EBD, only connecting up the J5 and J6 from the transformer (nothing continuing out into the machine yet, until I know the voltages are right)...

I checked the test points... and got 45V at TP3 !?!?!?!? How is this possible, it's a different (and just tested as working) board?!

Now I know some of the voltages can be a bit different if you don't have the outputs connected, but back in the Centaur this board was reading fine with just J5 and J6 (the power in) connected. Now it's got the same issue as the other board when it's moved to the EBD?

I should point out that I checked the voltages out from the EBD transformer by sticking the DMM probes into the J5 and J6 plugs, they were all perfect. I also checked the voltages on the board at the points between CR5-CR6 and CR8-CR7 where there is 14.2 VAC as expected. I think this rules out an issue with the plugs (I checked the same for all the other points where the AC from the transformer comes into the board). I also compared that the wiring of the plugs from the transformers are identical between EBD and Centaur, and that the plugs aren't damaged and did continuity checks between them looking for a short circuit between pins in there.

So in summary everything looks fine, right up until TP3 where it suddenly gets 45V.

The only thing plugged into the board between the machines is J5 and J6 - nothing else. So if there's a problem in EBD it must be coming from the transformer? The transformer really isn't under any load, is that a thing that transformers can provide different voltages when at rest or under load and does it apply here?

I have tried just plugging in J5 or J6 on their own, here's the results, do they make any sense?
Just J5: TP1=0, TP2=195, TP3=2 (should be zero), TP4=7.5, TP5=47
Just J6: TP1=8, TP2=12 (should be zero), TP3=20 (great, not 45, but?), TP4=4.1 (should be zero), TP5=0

In writing this, I've had an idea to put something like a cloth or some wood down underneath the board just to make sure nothing is touching that metal plate the BR's are normally thermally pasted down on to and somehow conducting current from one place to another. I'll check that and update this tomorrow.

Thanks for reading and all suggestions very welcome.

EBD power (resized).png
#2 65 days ago
Quoted from m4tt:

found that TP3 on the rectifier board was reading 15.9V when it should be 11.9V.

This occurrence is normal.
11.9V is the spec unloaded voltage when the solenoid driver board is *not* connected. When the solenoid driver board is connected, its capacitor at C23 stores energy on that supply rail and brings up the voltage.

Quoted from m4tt:

I checked the voltages again and found 48V at TP3

Quoted from m4tt:

I checked the test points... and got 45V at TP3

Your multi-meter is giving a false reading from noise it's picking up. You need a load on that supply rail to measure it properly. Hook up a 12V lamp across that test-point to ground and remeasure it.
Also check that the ground prong on your power cable has zero ohms continuity to ground in the machine and to the GND test-point on the rectifier board.

Your question has come up before:
https://pinside.com/pinball/forum/topic/bally-as-2518-54-rectifier-boardtest-point-voltages-too-hot
https://pinside.com/pinball/forum/topic/bally-as-2518-transformer-wiring
https://pinside.com/pinball/forum/topic/bally-54-rectifier-board-12-volt-problem#post-4991448

#3 65 days ago

Yes what Quench said.

Anyway, with power off, check that CR5/CR6 connection is at ground (0 ohms). And also check that TP5 and TP3 are not connected with each other (because of the rectifiers that would not cause a short and smoke, but raise the voltage on TP3 to TP5 level).

To reduce multimeter sensitivity, it is enough to connect a 10-100k resistor across meter leads. Often that can be done by inserting resistor leads to multimeter sockets before plugging in the test leads.

#4 64 days ago

Quench Thanks for the answers and those other links for some extra reading. I put a 12V lamp across TP3 and GND and got a 10V reading (see pic below). I also tried my old crappy DMM and that showed 15V with no load (!) - I'm a bit embarrassed that I didn't try it earlier. I just assumed that because all other readings were right, it wouldn't be doing something weird on just one.

I did try turning off the auto-range but that didn't make any difference.

I also checked all my grounds, from the earth pin on the plug to the ground braid running around the cabinet and to the GND test point as I plugged back in each of the four other plugs that go out the machine. They were all ok (not zero ohms but close) except the playfield plug which doesn't seem to be connected, so I'll investigate further.

Tuukka I think you meant GND to CR5/CR8, and that's fine. Then regarding TP5 to TP3 there is actually connectivity one way between these as there's that 600 ohm resistor across the bridge. This was threw me early on when I was testing continuity all over the board, but I think it's as it's supposed to be.

So now I feel like I'm never going to fully trust a DMM. Can you explain why this particular test point does this? Where else might I come across this type of thing in a pinball? Where could the noise be coming from? What is the DMM trying to do? Why do I get normal readings from the board in one machine but this noisy reading from the *same* board when it's in a different machine?

2021-08-18 13.23.36 (resized).jpg
#5 63 days ago
Quoted from m4tt:

Why do I get normal readings from the board in one machine but this noisy reading from the *same* board when it's in a different machine?

What's the chance the noise is from the ballast running the flouro tube in the backbox? If you disconnect it does it make a difference?

Quoted from m4tt:

So now I feel like I'm never going to fully trust a DMM. Can you explain why this particular test point does this?

I haven't personally seen it (maybe because my Fluke multi-meter gives a correct reading). It seems to affect some multi-meters and not others.
An oscilloscope would probably help to see what's being picked up.

Quoted from m4tt:

Where else might I come across this type of thing in a pinball?

People often get a low reading on TP2 of around 160V, caused by the resistor at R3 on the rectifier board which was probably put there to limit current draw from the analog multi-meters used back in the day.

#6 62 days ago
Quoted from Quench:

What's the chance the noise is from the ballast running the flouro tube in the backbox? If you disconnect it does it make a difference?

I had it disconnected so no, not from the ballast.

Quoted from Quench:

People often get a low reading on TP2 of around 160V, caused by the resistor at R3 on the rectifier board which was probably put there to limit current draw from the analog multi-meters used back in the day.

Good to know, yeah that resistor is just for the test point, I wondered why it was even there.

Quoted from Quench:

An oscilloscope would probably help to see what's being picked up.

So you're thinking it's possibly a really quick high voltage spike, perhaps jumping up even higher than 50V but just for a short amount of time? So the DMM is sort of "averaging" it out? Is it most likely coming from interference or induction from something nearby? With the only thing plugged in being the transformer, maybe that's doing something a bit weird that isn't showing up on the AC tests?

I'll have a look around for cheap oscillator options (as it's not really a high priority, but I am curious) I think there are phone apps/kits, but I don't know how good they are, as I've seen people mention oscilloscopes as being a better tool, but I don't really know how best to use one to diagnose this sort of issue further.

#7 61 days ago
Quoted from m4tt:

So you're thinking it's possibly a really quick high voltage spike, perhaps jumping up even higher than 50V but just for a short amount of time?

Was thinking along the lines of EMI. Can depend on how wires are running in the transformers power looms, etc. In combination with the input capacitance of that multi-meter that's giving you the false high voltage reading with no load. Try the 100k resistor as Tuukka suggested to see if it negates it.

Anyway with the circuit loaded and your other meter giving readings in range, I'm not sure there's much point trying to "fix" this as it won't be the cause of your original boot issue.

#8 61 days ago

On an unloaded power line - you can get voltage induced into that wire from a nearby source wire (e.g. solenoid wire). But in order to see this induced phantom voltage, you need to have a very high impedance input on your meter. A high impedance meter typically has a very high input resistance and adds very little loading to the voltage being measured. Very typical of a DMM type meter.

The old analog meters didn't have a problem reading unloaded voltages because they introduced their own loading into the circuit which eliminated the phantom voltages. DMM meters add very little load to the circuit being measured so they will sometimes see wildly high voltages on unloaded circuits.

First learned of this when training to be an electrician a thousand years ago. I used a DMM in an outlet to make sure it was dead -- it read 120VAC. Checked breaker - it was off. Remeasured - 120VAC. Guy training me laughed and moved an adjacent wire away by an inch or two. Lo and behold - voltage then went to zero.

Moral of the story - if you see a wild voltage on an unloaded power source, remeasure using an old analog meter to make sure it isn't a phantom voltage reading. Or throw a resistor between power and ground and remeasure.

#9 61 days ago

I have a Simpson 260 meter for these exact reasons. Plus, I love the dB scale for audio.

#10 60 days ago
Quoted from G-P-E:

On an unloaded power line - you can get voltage induced into that wire from a nearby source wire (e.g. solenoid wire). But in order to see this induced phantom voltage, you need to have a very high impedance input on your meter. A high impedance meter typically has a very high input resistance and adds very little loading to the voltage being measured. Very typical of a DMM type meter.
The old analog meters didn't have a problem reading unloaded voltages because they introduced their own loading into the circuit which eliminated the phantom voltages. DMM meters add very little load to the circuit being measured so they will sometimes see wildly high voltages on unloaded circuits.
First learned of this when training to be an electrician a thousand years ago. I used a DMM in an outlet to make sure it was dead -- it read 120VAC. Checked breaker - it was off. Remeasured - 120VAC. Guy training me laughed and moved an adjacent wire away by an inch or two. Lo and behold - voltage then went to zero.
Moral of the story - if you see a wild voltage on an unloaded power source, remeasure using an old analog meter to make sure it isn't a phantom voltage reading. Or throw a resistor between power and ground and remeasure.

I've always wanted to add an analog meter to my hoard of tools, now I have an excuse to finally make that happen

Thanks for sharing this informative post, Ed!

#11 60 days ago
Quoted from frunch:

I've always wanted to add an analog meter to my hoard of tools, now I have an excuse to finally make that happen
//<![CDATA[
window.__mirage2 = {petok:"f658e623e692c2910f11a422db82bbea24bf1072-1629569633-1800"};
//]]>

Thanks for sharing this informative post, Ed!

Simpson 260s are wonderful. Many generations out there. You can almost calibrate them yourself.

If you are buying from Ebay, just be careful of shipping (obviously). Make sure seller puts it in a way oversized box with lots of bubble wrap. Also, make sure you get a pic of the battery compartment to make sure it is clean.

#12 60 days ago
Quoted from Skidave:

Also, make sure you get a pic of the battery compartment to make sure it is clean.

Indeed. I have a cabinet with 40 or so analog multi-meters I had to move recently only to discover my dad left batteries in all of them 10-15 years ago. Oh dear..

Hey there! Got a moment?

Great to see you're enjoying Pinside! Did you know Pinside is able to run thanks to donations from our visitors? Please donate to Pinside, support the site and get anext to your username to show for it! Donate to Pinside