Lamp Matrix MOSFET upgrade on sys 9 MPU?

(Topic ID: 221804)

Lamp Matrix MOSFET upgrade on sys 9 MPU?


By 72Devilz

3 months ago



Topic Stats

  • 7 posts
  • 4 Pinsiders participating
  • Latest reply 3 months ago by barakandl
  • Topic is favorited by 2 Pinsiders

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#1 3 months ago

Since system 9 MPU boards are getting more and more rare I am contemplating performing the MOSFET upgrade to the lamp matrix on the MPU in my Space Shuttle. My board was purchased NoS about 5 years ago and it has the cement resistors, recently I had an issue with some controlled lights and while troubleshooting I noticed that two of the resistors were getting extremely hot and one had almost backed its way out of the solder point creating a poor electrical connection. I have tested, cleaned and re-soldered the resistors back in place but there has been some heat transfer and discoloration on the board. For obvious reasons I want to remedy this issue so the board lasts for many more years. I am no stranger to board work but I am hesitant until I get some feedback from some others who have successfully performed this upgrade as I have seen two methods one using jumpers in place of the resistors and another method lowering the working voltage using 1k ohm resistors. If you have performed this upgrade on a system 9 MPU in particular please give your feedback, pictures, materials list or links to existing documentation for this procedure if possible. TIA!

#2 3 months ago

Bump

#3 3 months ago

never done it to sys 9 but it works fine in sys 3-7 and 11. Considering the circuit didnt change, sys 9 should be fine.

There have been reports of exploding mosfets and predrivers because the Vgs rating is close to maximum. I use legit FQP17P06 and never had trouble. Do know there are counterfeit mosfets out there and I suspect that might be at least part of the cause of reported failures.

The voltage dividing setup is best, but I have gotten away with using a 1K 1W(just so it fits better) instead of the 27ohm 5w. I would not recommend using zero ohm resistor. A resistor like 1K can still turn on the gate, but allow current limiting if the mosfet shorts.

#4 3 months ago

PinWiki has the procedure for System 11 and maybe others. The circuit and process is identical.

Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

#5 3 months ago

Careful, sys9 doesn't like MOSFETS. Be sure to do it the 'better new way' on PinWiki

Once MOSFETs are substituted for the TIPs in the lamp driver circuit, it is possible to replace the 27 ohm resistors with simple jumpers or even leave the 27 ohm resistors in place if they are in good shape as the low resistance will have a negligible effect on the operation of the MOSFET. However, the problem with either of these is that the MOSFETs are driven by 18 VDC Source to Gate voltage which is dangerously close to the absolute maximum rating of the IRF9530 and IRF9Z34 of 20 VDC (this also holds true for Data East MPUs). The FQP17P06 has a higher Vgs rating (25VDC) than either the IRF9530 or IRF9Z34N - but you are still driving the part at over 70% of its absolute maximum. Typical uses for these MOSFETs drive them by about 10 VDC Source to Gate voltage (or -10V for P-Channel MOSFET's used here).
http://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#MOSFETs_Installed_in_a_System_9_MPU_Board

OR ELSE!

https://pinside.com/pinball/forum/topic/controlled-lamps-too-bright-lamp-matrix-problem

#6 3 months ago

I appreciate the feedback guys! Here is another idea, since there is an issue with excessive heat on two of the channels another idea I have is installing a larger resistor or even attaching a heatsink to help dissipate the heat, if I leave the board as is and play it as little as I do the board will last a few more years before the heat does irreversible damage at those locations. I've even considered moving all the matrix resistors off board to eliminate the possibility of heat all together. Just curious what others have done in this case. TIA!

#7 3 months ago
Quoted from 72Devilz:

I appreciate the feedback guys! Here is another idea, since there is an issue with excessive heat on two of the channels another idea I have is installing a larger resistor or even attaching a heatsink to help dissipate the heat, if I leave the board as is and play it as little as I do the board will last a few more years before the heat does irreversible damage at those locations. I've even considered moving all the matrix resistors off board to eliminate the possibility of heat all together. Just curious what others have done in this case. TIA!

burning up resistors is usually a symptom of a stuck on lamp circuit. They are constantly strobed, but when they lock on for whatever reason be it a blown 7408 blanking chip or the main transistor itself, those resistors can burn up. So if just one or two resistors get hot enough to burn a 5w resistor then something else is probably wrong.

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