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50v coil misbehaving (Sega / DE)

edsr

edsr

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Joined
Oct 7, 2017
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415
Location
Cheltenham
I got the wires back to front on the upper VUK (earthquake) coil.

This blew F5. I realised what I’d done and corrected it.

Bear in mind I don’t have a dmd currently so can’t see any messages.

1. I fired the machine up and pulled out the upper coin door switch in order to get a test game to play. Everything was perfect until the ball went in the upper VUK and F8 blew.

2. I checked the PPB and everything seemed fine - diodes and transistors all flow/block as they should and give virtually identical readings. Then checked the CPU (on bench) and got the same - all readings almost identical. Also did continuity tests to Gnd on the board, from the transistor tabs, AOK. The same when refitted to the back box.

3. Then checked the diode on the VUK coil and it was blown.

4. Having replaced the diode, I fired the machine up and pulled out the coin door switch - the VUK plunger just sticks up out of the play field (giving me the finger). So I push the coin door switch back in, it drops, and then with coin door closed, if i press either flipper button, it just raises and lowers (slowly) with each press!

I thought I had it sussed with the diode on the coil, although was fully expecting to replace Q42/Q4 but again they test just fine as far as I can tell.

I was gonna just start replacing all the transistors on the 50v section of the CPU and all the diodes on the 50v coils but that felt unnecessary given the tests and creates scope for more problems so I thought I’d ask you guys your opinions first.

Should I just start replacing transistors even if they test OK, or start looking upstream?

Is there a way to test the signal from the IC to the smaller transistor with the game on and F8 removed?

@Moonraker has already been a star and pinged me a few tips.
 
Well if it was me i'd replace the drive and pre drive transistors.
The way your lucks running with this machine could i respectfully suggest that maybe pinball ain't for you and you should find a hobby less demanding and easier like knitting.
Let us know how you get on with the transistors.
 
Cool I’ll give that a go - Moonraker suggests the same but that was before the diode was known to be faulty and actual readings taken on the drive/pd transistors.

I’ll post back when I’ve had a chance to swap them out - I’ve got five of each so I’ll give that a shot.


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paddythegreek said:
Well if it was me i'd replace the drive and pre drive transistors.
The way your lucks running with this machine could i respectfully suggest that maybe pinball ain't for you and you should find a hobby less demanding and easier like knitting.
Let us know how you get on with the transistors.
Click to expand...

Can always rely on you for inspirational and motivational pep talks :D

Just cause you didn't get a tumbler for Christmas doesn't mean you can take it out on us :rofl:
 
Ah but i got a birthday comin up in march and i've informed the bu**ers i may change my will if things don't "appear"
Sorry edsr for hijacking yr thread
 
LOL any time!! :) if my luck continues there may be a used tumbler for sale, along with a BW project ;)


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Ok so that was a f******* nightmare of a job and still hasn’t fixed it.

Whats next? Upstream?
 
Last edited:
Let's have some pics of the coil please..
 
Thanks Arv - coil looks fine visually and gives almost identical resistance readings as others of same size. But... with power off, I ran a continuity test to ground from both tabs of all coils on that circuit - all beeped so started looking for a short to gnd. Started working back to the cpu from the un-banded side of the diode and found that Q4 had gone (even though before I changed the coil diode and had the PPB ‘on the bench’ I’m certain it tested fine!). Anyway that’s looking like the culprit but have to wait till wed/thu for new TIP36C to arrive [emoji30] and then hope nothing else pops when I replace Q4.

Here’s a pic of the coil anyway... uploads.tapatalk_cdn.com_20180108_7c99323e11da9d0f41d576fefa6e7a2c.jpg
 
upload_2018-1-8_16-58-29.png

Is that touching? Put some insulting tape around it.
 
Nah it’s an optical illusion looks like it is tho! I can actually put my finger between the screw head and terminal.


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Just an idea but I had a DE mech coil that measured ohms ok but when exercised its drive transistor intermittently blew. I swapped the coil out as perhaps the windings were shorting when under load and heat. Been working fine ever since.
 
Thanks again Astyy. Have ordered 2 x Q4 replacements - if I blow the new one then I’ll swap it out and put a new coil in. [emoji106]


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Wooooop! Swapped out Q4 and just played my first game (minus a DMD) for around 2 months. Thanks everyone who helped sort this : )




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