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Blowing TIP102


robm

Question

Looked at a T2 today that was working fine, then the plunger coil locked on, blowing Q58 as well as the associated fuse. So i took the power driver board home, replaced Q58 (TIP102), plus its 5401 predriver, as well as the diode.

 

I put the repaired power driver board in a Dr Who at home, and it worked fine, with all coils firing and no lock ons.

 

So this morning i took it back to old mates place, put the repaired PD board back in, started a game and the transistor was blew straight away.....

 

So then i looked at the coil itself - resistance was around 3.5 ohms, so prob OK. I then got the kickback coil (same one - i think its 23-800), and put it in the plunger, put another diode, TIP102,5401 in PD board, and same problem again.

 

Any ideas - its obviously not the coil, the coil lugs are clear of any earthable objects, so i'm leaning towards a wiring short - although seems very unlikely as it happened out of the blue when the bloke powered the machine on. Power driver board problem seems unlikely as i thought i would have picked it up in Dr Who?

 

Any ideas on what more or how to test?

 

Thanks

 

Rob

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Interesting. Would seem you've isolated the problem to the T2 machine itself (and not the PD board).

 

Any chance that when the playfield is in the lowered position there is something that is causing a short?

 

Check the connector on the PD board that supply power to the coil. Are the pins tarnished or has the plastic connector suffered some heat damage that may mean a couple of crimp pins are touching and shorting out?

 

 

These a just a couple of stabs in the dark.

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To follow this up, i decided to take another power driver board over. Checked the switch in shooter lane, and all good. Fired it up and it works perfectly. So i am suspecting that U4 or U5 which control the TIPs has been destroyed. Although i'm still scratching my head why it worked in Dr Who - and it does use the same Q58 transistor for one of the slings... Anyway, i left the working board with him and will hopefully repair this one soon
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Well, if the board works 100% in another machine then that can only leave what's left in the faulty machine to be causing the fault, if that makes sense. So I would be double/triple checking wiring and coil diodes.
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My guess is to check the status of the switches in that matrix to see if any coil switches are stuck on especially if they are sharing the sling shot switch matrix those blades can get stuck together ( sometimes a stuck ball can short out the blades) or a short in a switch wire to ground, reason why with the earlier WPC machines the coil switches didn't pulse when they got stuck and I believe T2 was an early WPC DMD release which may not have the pulsing function to prevent transistors from blowing when you had a stuck switch whereas Dr Who would now have this fail safe feature, hence why it worked OK in DW. Best practice is to fuse each coil in these known area's to prevent these problems. If your familiar with Gottlieb DMD machines they have practically every coil/motor fused to keep the game playing, good design.

Good Luck.

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