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One for the boffins

The original question was to explain the DC offset in the waveform and that is due to the 'ideal' diode bridge being a diode voltage drop different to the normal ground and therefore you will see an approximate 0.6v offset depending on the scope ground point reference.

David
 
DAFlippers said:
The original question was to explain the DC offset in the waveform and that is due to the 'ideal' diode bridge being a diode voltage drop different to the normal ground and therefore you will see an approximate 0.6v offset depending on the scope ground point reference.

David
Click to expand...

i sort of get it 😃
 
Isn't part of the issue that there is a ground loop of sorts? Maybe I'm misunderstanding, but it sounds like you have this arrangement for grounds:

Code: 
+-----+      +-----+
| MPU +------+ OCD |
+--+--+      +---+-+
   |             |
   |  +-------+  |
   `--+ Chase +-´
      +-------+

I read somewhere on the internet that ground loops are bad :hmm:
 
That's right, but only because the OCD creates a different ground potential by converting the 6.3VAC signal to V+ and ground using the ideal diode bridge. So the diagram is more like this:


Code: 
+-------------+     6.3vac     +-----+    
| TRANSFORMER |    ------------| MPU +---\
+-------------+                +--+--+    GND
               \  6.3vac     +-----+    (loop)
                ------------| OCD +---/
                            +--+--+



Because the ground provided by the MPU is different to the ground generated by the OCD (by 0.6v) the AC signal shifts 'up' by 0.6V resulting in LEDs facing the wrong way to appear dimmer than LEDs facing the right way (by 1.2v, ie, 0.6 x 2).

See @Vimtoman, I do know whats going on!! :)
 
Incidentally, as part of this testing, I've had to do A/B testing of both the GI OCD and the Afterglow, and I've got to say, the Afterglow has a much smoother fading effect.
 
Surprised it took you lot so long to work out the problem😵🤡

I put an ledocd in my FT as there were no Afterglows available at the time ( other pins had them in ) then some became available by your good self so ordered some.
I did a comparison with both and sold the ledocd board as I couldn’t see much difference, if anything the Afterglow looked a bit better to my eyes.
 
stumblor said:
That's right, but only because the OCD creates a different ground potential by converting the 6.3VAC signal to V+ and ground using the ideal diode bridge. So the diagram is more like this:


Code: 
+-------------+     6.3vac     +-----+   
| TRANSFORMER |    ------------| MPU +---\
+-------------+                +--+--+    GND
               \  6.3vac     +-----+    (loop)
                ------------| OCD +---/
                            +--+--+



Because the ground provided by the MPU is different to the ground generated by the OCD (by 0.6v) the AC signal shifts 'up' by 0.6V resulting in LEDs facing the wrong way to appear dimmer than LEDs facing the right way (by 1.2v, ie, 0.6 x 2).

See @Vimtoman, I do know whats going on!! :)
Click to expand...
So you understand what I said :cool:

David
 
stumblor said:
That's right, but only because the OCD creates a different ground potential by converting the 6.3VAC signal to V+ and ground using the ideal diode bridge. So the diagram is more like this:


Code: 
+-------------+     6.3vac     +-----+  
| TRANSFORMER |    ------------| MPU +---\
+-------------+                +--+--+    GND
               \  6.3vac     +-----+    (loop)
                ------------| OCD +---/
                            +--+--+



Because the ground provided by the MPU is different to the ground generated by the OCD (by 0.6v) the AC signal shifts 'up' by 0.6V resulting in LEDs facing the wrong way to appear dimmer than LEDs facing the right way (by 1.2v, ie, 0.6 x 2).

See @Vimtoman, I do know whats going on!! :)
Click to expand...

Dont think the problem is GND :rofl: changed my mind :rofl:

@stumblor only connect to the Afterglow insert cable with unsing J120 pins 2,3,6,8,9,11

The Chase wires will still plug into the original J120 using pins 1,5,7,10

So you need to make a splitter cable seperating and rerouting the wires to afterglow and driver board.

J115 to go to the driver board and the Afterglow J6. No need to lift wire 1..

Think that should allow you to run power off J115 and run your chase light pcb with bulbs.
 
Haha let's not re-open the can of worms! 😃

The J120 splitter idea was the first one I went with actually, and results in the following..

a) WITHOUT J120-1 connected, both fire up and run, but the chase board exhibits reversed LEDs at reduced brightness (normal facing LEDs run fine)
b) WITH J120-1 connected, GI OCD/Afterglow main fuse blows

I actually didn't bother re-routing any of the J120 wires, just plugged straight into AGGI and created a new cable to pull J120 1,5,7,10 to send to Chase. In any case, it has the problem a) which was a deal breaker so had to look at other options.
 
stumblor said:
Haha let's not re-open the can of worms! 😃

The J120 splitter idea was the first one I went with actually, and results in the following..

a) WITHOUT J120-1 connected, both fire up and run, but the chase board exhibits reversed LEDs at reduced brightness (normal facing LEDs run fine)
b) WITH J120-1 connected, GI OCD/Afterglow main fuse blows

I actually didn't bother re-routing any of the J120 wires, just plugged straight into AGGI and created a new cable to pull J120 1,5,7,10 to send to Chase. In any case, it has the problem a) which was a deal breaker so had to look at other options.
Click to expand...
You have to separate the chase and playfield GI connections that connect to J120 and connect respectively to the wpc driver board and afterglow.

Chase connects to driver board J120 using pins 1,5,7,10 (Not to afterglow)
Playfield GI to Afterglow J120 pins 2,3,6,8,9,11 (Not to Driver board)

Split the cable plugging into driver board J115 to supply
WPC J115
Afterglow J6
 
Last edited:
Vimtoman said:
Dont think the problem is GND :rofl: changed my mind :rofl:

@stumblor only connect to the Afterglow insert cable with unsing J120 pins 2,3,6,8,9,11

The Chase wires will still plug into the original J120 using pins 1,5,7,10

So you need to make a splitter cable seperating and rerouting the wires to afterglow and driver board.

J115 to go to the driver board and the Afterglow J6. No need to lift wire 1..

Think that should allow you to run power off J115 and run your chase light pcb with bulbs.
Click to expand...
@Vimtoman If you don't think it is the different potential 'grounds' then what do you think is the cause?

David
 
For the chase conflict its the joining of the chase drive circuit and Afterglow drive circuit.

They are both driving the same connections.

The chase drive has its own triacs but also uses the Drive board triacs on J120

But seeing that they are not sharing the same lines we can split them.
Afterglow running GI leds no connections to drive board except J115
Chase drive bulbs using J115 and J120 on drive board

Again having a schematic of how @stumblor has connected all this helps.

@stumblor has not mentioned seperating the J120 J121 cable connections so I assume all is connecting to the Afterglow.

If he has done this then yes we can go back to the GND cause but in this case I think maybe its a connect up issue.
 
Last edited:
"Again having a schematic of how @stumblor has connected all this helps."

What I asked for yesterday.

The DC offset on the Waveform is pertinent.

David
 
Sorry guys! all a bit hectic here at the moment. Will try @Vimtoman wiring suggestion and provide feedback (and schematics) soon.
 
OK, don't shoot me on this, I've been following this thread and take my hat off to the level of electronics technical knowledge but is it too simplistic to simply turn the dim LEDs round the other way?
 
100% could do this, yeah, and if it was just my machine, I would probably just do this and forget about it. However I'm currently building an alternate Chase board, and having to tell users that they need to do an hours worth of LED fiddling (because of an unsolved bug) doesn't go down too well! ;-)
 
stumblor said:
100% could do this, yeah, and if it was just my machine, I would probably just do this and forget about it. However I'm currently building an alternate Chase board, and having to tell users that they need to do an hours worth of LED fiddling (because of an unsolved bug) doesn't go down too well! ;-)
Click to expand...
Fair enough, would seem like a bit of a faff if I'd bought one and had to do that. From a personal point of view I too would need to understand the cause so I completely get it! Was just curious.

Pete
 
stumblor said:
Incidentally, as part of this testing, I've had to do A/B testing of both the GI OCD and the Afterglow, and I've got to say, the Afterglow has a much smoother fading effect.
Click to expand...
You can adjust the fading in software.
 
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