(Topic ID: 233550)

Help! Messed up my sorcerer doing the mosfet mod!!


By Oldschool77

5 months ago



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  • 10 posts
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  • Latest reply 5 months ago by Oldschool77
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#1 5 months ago

It wasn't broke, so i "fixed it"! ........So i had parts left over from doing the Mosfet upgrade to the lamp matrix on my Firepower 2 (System 7), so.....new game, new bulletproofing..... i decided to do the same on my perfectly working zero issue Williams Sorcerer (System 9)....well i didn't do my homework (I got this...... right!!??) enough to realize before hand that it doesn't always go well on system 9, AND it's not the same simple procedure of swap out, and zero ohm jumpers in place of the hot old resistors. Day late, and a dollar short, i now have 18 VDC all the time on all lamps from column 1 of my lamp matrix (see pic) and on pin 1 ONLY of 1J7. They are blindingly bright, and they do cycle slightly dimmer as they "flash" so i don't think i fried my PIA (seems to be trying to turn them on and off in attract mode as they should be, they just go from surface of the sun bright to almost as bright as they get "turned" off and on with the attract mode). I tried replacing Q23 again with a fresh Mosfet twice thinking i had a bad one and same issue. Quadruple checked for solder bridges and/or loose solder, and from what i can tell the pre-driver transistor is still fine. I did no other mods, and didn't lift the playfield when i did this, so i think i can rule out shorting anything underneath.

I then returned everything back to stock (transistors and resistors)...... no change. Then I replaced the PIA.....no change. I tested all the transistors and drive transistors that feed column 1 (without removing them) and they all seemed fine. I feel like I must have a solder bridge our loose solder somewhere but I went over every inch of the mpu and found nothing, and no shorted/bridged transistors.

Side note, if i go to lamp test they turn completely on and completely off like normal as they are pulsed. And when they are "on" they are normal and uniform brightness, not super insanely bright.

Any ideas on where else or what else to check? They occasionally dim slightly as the attract mode does it's thing. But only the slightest, further thinking I have a bridge somewhere. Side note....with J6 and J7 (power and return for the lamps) unplugged I still have 18vdc at 1J71 so it's definitely on the board, not some sort of external short or whatnot.

Help!

Fyi I cannot access pinside at work so I may be a bit delayed in my responses. thanks!!

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#2 5 months ago

It also may be worth noting that U58 and SR5 are considerably warmer then their similar surrounding counterparts.

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#3 5 months ago

Check the part number on the MOSFETs. If you went with IRF9Z34's -- make sure you didn't get IRF934's instead.

#4 5 months ago

I'll look tonight but right now everything is back to stock so I would think that would not affect my current situation. Also don't forget this is the same batch of transistors that I used on my firepower two and they did fine in there. At this point, with everything back to stock, I'm just trying to figure out what I damaged so I can fix it. Lol

#5 5 months ago

Sounds to me like you wired something wrong for that particular row or column thats acting up.

Check and recheck the pictures shown on pinwiki to make sure yours matches.

#6 5 months ago
Quoted from SarverSystems:

Sounds to me like you wired something wrong for that particular row or column thats acting up.
Check and recheck the pictures shown on pinwiki to make sure yours matches.

I wish it was that easy, the transistors are facing the right direction, and you cant put resistors on backwards. Remember with all jacks unplugged except the mpu power I'm still getting 18vdc for that row only.

#7 5 months ago

Not necessarily polarity, but more along the lines of maybe you have a solder bridge, or one of the resistors is connected to the wrong leg of the FET.

Do all of the components test OK outside of the circuit? Maybe you have a bad FET?

#8 5 months ago

The system 9-11 games (and DE/S) must operate at different voltages / timings as people run into trouble with these games when they put in mosfets for the lamp column drivers.

When you run into problem and the mosfet goes kapow and there is a zero ohm jumper link it also kills the predriver ... 2n6427 i think it is.....

I'd replace the pre drivers. (you can cheat if using mosfets and just use a general transistor). Replace the mosfets (probably drain to source shorted). Do the voltage divide mod.

FQP17P06 has a better Vgs rating than the IRF9Z34... but either way they have been known to go bang in sys 9/11/DE/Sega without the V divide mod. Done the typical application with without the v divide mod to hundreds of WMS 3-7 driver boards and never trouble on those.... its something with the later games.

Even if on sys 3-7 games don't use zero ohm links. If you had a resistor in there between the predriver and mosfet it can limit current when things go bad ... like maybe saving the predrivers. Leave the original 27R in if not toasty or anything up to like 10KR would be fine.

Warning about transistors.... buy from authorized distributors and not China. Most stuff from China is OK but the knock off power transistors are usually not okay unless you de-rate heavy. Usually not really any cheaper either than places like Arrow. I some times wonder when these posts come up where the part came from.

The a logic probe you can check the 7408 where the PIA signal ANDs with the blanking signal. You should get the same wave form from the pia as the 7408 out going to the predriver. Compare to working columns if not sure.

#9 5 months ago
Quoted from barakandl:

The system 9-11 games (and DE/S) must operate at different voltages / timings as people run into trouble with these games when they put in mosfets for the lamp column drivers.
When you run into problem and the mosfet goes kapow and there is a zero ohm jumper link it also kills the predriver ... 2n6427 i think it is.....
I'd replace the pre drivers. (you can cheat if using mosfets and just use a general transistor). Replace the mosfets (probably drain to source shorted). Do the voltage divide mod.
FQP17P06 has a better Vgs rating than the IRF9Z34... but either way they have been known to go bang in sys 9/11/DE/Sega without the V divide mod. Done the typical application with without the v divide mod to hundreds of WMS 3-7 driver boards and never trouble on those.... its something with the later games.
Even if on sys 3-7 games don't use zero ohm links. If you had a resistor in there between the predriver and mosfet it can limit current when things go bad ... like maybe saving the predrivers. Leave the original 27R in if not toasty or anything up to like 10KR would be fine.
Warning about transistors.... buy from authorized distributors and not China. Most stuff from China is OK but the knock off power transistors are usually not okay unless you de-rate heavy. Usually not really any cheaper either than places like Arrow. I some times wonder when these posts come up where the part came from.
The a logic probe you can check the 7408 where the PIA signal ANDs with the blanking signal. You should get the same wave form from the pia as the 7408 out going to the predriver. Compare to working columns if not sure.

Awesome info thank you! I'm gonna "borrow" a pre driver (since parts are almost a week away) from the one next to it and see if the issue goes away.

#10 5 months ago

Turned out to be Q15....the drive transistor as you suggested. Thanks for all the help!! Side note.....it checked out good with my meter on and off the board....so it must be a case of it only goes bad under load. Good lesson learned now!

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