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Pi2Jamma Display Corruption

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sapporo46 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Topic: Pi2Jamma Display Corruption
    Posted: 03 Mar 2019 at 11:18pm
Did a very stupid thing and powered on the cab with a Pi2Jamma setup connected, but the PSU was running at 5.5. Considerable smoke and about 7 seconds of damage before I powered it off, now the display is corrupted Cry



Looks like the pins on the GPIO connector have been fried, pretty sure I know the answer but don't suppose I have any repair options here as the Pi2Jamma board is custom made? The Pi3 of course is fine due to its voltage protection.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 04 Mar 2019 at 2:31am
Odd. I would have thought 5.5v is perfectly safe to run a Pi. 25v maybe not!.. but 5.5 is only 10% over. You sure you didn't connect the jamma board in backwards etc..?

Video out should be going via the HDMI socket, not the GPIO I think.
There should be a dongle convertor to convert to RGB / VGA on the board?
I'd take a look at replacing that perhaps.

For the GPIO pins, you could resolder them if they have fried. But I'd not expect to see smoke from there... surely there's a voltage regulator or something on the PCB that's gone.
You could try connecting it without the pi in and see what happens.


Edited by Flinnster - 04 Mar 2019 at 2:33am


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fantazia2 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Mar 2019 at 8:14am
The Pi2Jamma uses the GPIO with a Variant of the Gert VGA666 for video output.

There is also a video amp in place before the jamma connector to boost the voltages from the 1v the board produce up to what is needed by arcade monitors.

Each of the RGB colours uses I think 6 pins on the GPIO going through resistors to produce the analogue video signal.

Might be worth finding a game with a built in test screen to see what each of the RGB channels are doing. Is the picture solid as it looks like the sync is working.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Mar 2019 at 2:22pm
@Dave: it's quite likely that I plugged it in backwards... thinking about it I didn't exactly see where the smoke was coming from - but there's a short phono cable that runs from the Pi to the Pi2Jamma and some of the insulation on that had melted, this is probably where the smoke came from.

If I plugged the Pi2Jamma into the cab without the Pi, then I'd get no output - so what would that actually test?

My first concern was that I'd caused some damage to the cab, so I plugged it into my supergun setup instead and tested a few games. They don't look as bad as the splash screen, but it looks like some of the red colour is missing. The picture is solid, just looks like some of the colour data is trashed. I think I need to wire up a test switch in my cab, although I can think of one or two games that display test patterns before they start.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Posted: 04 Mar 2019 at 2:47pm
It uses a resistor ladder to convert the video output so you may have damaged some of them hence the broken colour output. They are all surface mounted unfortunately so tricky to replace without the proper kit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Posted: 04 Mar 2019 at 2:50pm
You could use a multimeter to test each resistor and see if the value matches the print on the PCB, that would rule them in or out
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 7:58am
Good shout Chunksin, I'll give that a try.

Thanks for the helpful replies all
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Bennett Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 12:06pm
So with the PI, you get all the RGB colours and white, but the video display contents are corrupt? (bad textures/objects).
http://www.philwip.com -sibling 'fix-off' (I’m losing by miles).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 4:33pm
I think it's the Pi2Jamma board corrupting the display - I just need to run an image which will let me run the pi with HDMI output as the Pi2Jamma software outputs the video at 15kHz
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 4:36pm
Here is an example of the display:

https://photos.app.goo.gl/L8uHnFBGr6UagQB56

But that game should look like this:

https://youtu.be/8F5qNagxuUc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 4:45pm
Originally posted by sapporo46 sapporo46 wrote:

@Dave: it's quite likely that I plugged it in backwards... thinking about it I didn't exactly see where the smoke was coming from - but there's a short phono cable that runs from the Pi to the Pi2Jamma and some of the insulation on that had melted, this is probably where the smoke came from.


Odd but possible I suppose. I'm not sure what's connected to pins 23/24/25/26 on that board, but you'd assume it's button inputs for buttons 2-5 for each player if it's standard jamma.
So firing 12v, -5v and 5v down those would probably do some damage to components linked to those pins and heading to GPIO pins related to the inputs.
I really can't explain the audio cable melting! Maybe once the GPIO was damaged there were high voltages flying across shorted components where they really shouldn't go?

Quote
If I plugged the Pi2Jamma into the cab without the Pi, then I'd get no output - so what would that actually test?

It would just serve to test what the state of that PCB is in now. Does it still smoke etc.. to fathom out what is broken and what might be repairable.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 4:47pm
Originally posted by sapporo46 sapporo46 wrote:

I think it's the Pi2Jamma board corrupting the display - I just need to run an image which will let me run the pi with HDMI output as the Pi2Jamma software outputs the video at 15kHz


If you connect a modern-ish flat panel TV with VGA-in, it should still be able to detect 15Khz modes, I think...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 11:00pm
The resistor ladder looks OK under magnification, and the resistances are all in tolerance I believe (measured with the multimeter set to 20K Ohms). Details are here.

I've looked at the GPIO pins under a jewellers loupe and it looks like there is evidence of burning there.

Bit of a mystery this Confused

If they weren't so expensive I'd just buy another one! Which I may well do anyway.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Bennett Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 11:17pm
I had thought you’d knacked the processor/GPU, as it can clearly do the main colours including black and white. However my brain struggles to know what a knacked DAC system would look like.

If you put your multimeter onto the diode setting, put the red probe on ground and the black probe on each GPIO pin, then are the readings similar for every pin?

Not that it’ll be fixable if it’s GPIO.
http://www.philwip.com -sibling 'fix-off' (I’m losing by miles).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fantazia2 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2019 at 11:50pm
The videos not the best to tell from but at 0:08 second mark, the lower registers on the green look missing which matches with the white colour bar showing purple in the lower part, you can see whats wrong when you compare it to a capture from mame. (Pic below)

In the picture of your board at the top the 8 pin surface mount IC is a video amplifier (Possibly a THS7314 or 7316), below that are 3 resistors that should be 75 ohms, these are connected between the output from the video amplifier and the jamma edge connector for the Red Green and Blue connectors.

The inputs to this amplifier are from the resistor ladders. Since you are getting an output then the traces between the input on the video amplifier and at least some part of the resistor ladder are intact.

Cant get my brain to work so cant remember which resistors do the darker shade of colour, possibly the higher resistance ones to give the lower voltage.

If you can check in the config.txt on the sd card to see what video mode its using I might be able to tell you which GPIO pins are being using for each of the colours. I think Ive got the image somewhere but dont have access to it at the moment.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 2019 at 8:18pm
Those three resistors are measuring 0.7 on 2K Ohm setting so I figure they're good.

However there are a few others which seemed to be out of spec - I'll try and measure them properly later.

On the SD card there's a config.txt and a config_pi2jamma.txt - the config.txt is as follows:

gpu_mem=64

disable_audio_dither=1
dtparam=audio=on
dtoverlay=vga666
enable_dpi_lcd=1
display_default_lcd=1
dpi_group=2
dpi_mode=87
hdmi_timings=320 1 16 30 34 240 1 2 3 22 0 0 0 60 0 6400000 1 #240p
#hdmi_timings=320 1 16 30 34 256 1 2 3 22 0 0 0 60 0 6400000 1 #256p

The only difference in the other file is that the 240p line is commented out instead of the 256p line.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 2019 at 10:35pm
There are 5 resistors to the right of the the 8 pin surface mount IC; I read these as:

3 x 100
12k
6.8k

The left 3 measure 100 ohms each, but the ones labelled as 12k and 6.8k measure 9.02 and 5.43 respectively. Don't know what they are for but looks like they might be damaged.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2019 at 10:01am
Config looks fine. That's honestly not your issue on this one.

Good luck with those resistors though - it'll be a nice fix if it's just those that need replacing.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote sapporo46 Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2019 at 2:55pm
It would... I can just about solder though - never mind surface mount
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2019 at 5:19pm
Yeah they are 'fun'. Easier to remove than put back on really.


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