Firepower 2 circuit board issues

[robm]

I picked up a Firepower 2 that needs some pretty serious work - it fires up, but no displays, makes some noise, can't start a game - one coil locks on.

The interboard connector is an absolute shocker - with half of it soldered in place, so 1st job is to put new female connectors on this.

I'm going through pinrepair and testing other components  on the driver board and just about all of the 2N4401 transistors are testing as bad.  Pinrepair says

Testing the 2N4401.
This is the pre-driver for TIP102 (or TIP102). Note if testing the 2n4401 "in circuit" (installed in the driver board), this transistor can test as "bad" (yet still be good), if it's controlling TTL 74xx chip is bad (which is actually fairly common).

Red DMM lead on center leg.
Black DMM lead on either leg.
.4 to .6 volts seen.

I get 0.5V on one leg (left one when i'm facing it) but only 0.25V on the other leg - does this indicate they are almost all bad (bar one or two) or as pinrepair suggests maybe the 7406 and 7408 IC's are all bad?

There are 3 resistors linked to each transistor, and one of these should be 2.7K ohms, and again, they almost only test between 1.8 - 2.01K ohms - should i replace these and do you think they are related to the transistor issue?

Only one of the TIP122 transistors seems bad.

Thanks

Rob

[Retropin]

Testing any transistor in circuit will have its faults. any readings are not to be relied upon - ive also NEVER had anywhere near some sort of reliable results using Clays methods.. i never test this way.

 2N4401 are just a signal transistor - generic replacements are at jaycar in the form of  PN100 or PN200... but...... rule of thumb is that if you have a LOT of one kind of transistor ( in this case 2N4401) and ALL results are the same, then this is normally the reading given for that transistor in that circuit.
In other words - the chance of ALL of them to be blown is very unlikely and in circuit you will get stray readings - only REAL test is out of circuit and with a resistance reading betwen all the gates forwards and reversed ( remember that current will only flow one way through B and C etc and should NEVER flow between C and E)

Pull one out - stop being lazy and test it - if it tests OK out of circuit then it is OK.. the time you spent posting on this forum would have determined this already.

If in circuit it tests bad but ALL the others test the same than you can 90% assume that they are good... but like i say - no real 100% guarantee on a test in circuit

[robm]

Thanks retropin

Took one out and it tested fine - so i can fairly safely assume they are mostly OK (except for the couple that were way out).

Do you thing the resistor values are a concern (ie: should be 2.7 k ohm but are 1.8 - 2.1 k ohm)?

[Retropin]

Mate - once again test out of circuit to be 100% sure - just lift one leg of the resistor though - no need to pull the whole thing out. Problem with testing anything in circuit is that the voltage you put across it with your DMM will take the path of least resistance and if there is a circuit to go around that is 2.1K and not 2.7K then it will take the lazy path ... electricity is a bit like teenagers really when you think about it

[FirePower]

Hi Rob,

Good to see someone taking on a basket case electronic board. I've never had any success in using the in circuit transistor measurement techniques described in the Pinrepair guide, but they are tremendous guides.

I've had some problems in this solenoid drive area on a WMS driver board, mine was a sys 6 game, but I think the FP2 uses the same board. In general comments I'd rate the chance of a 2N4401 being blown as pretty low, they are driven by logic level chips and drive the final TIP102. Much more likely to be the TIP102 blown, particularly if you have locked on solenoids. I'd be checking solenoid resistance and diode quality. (I suppose if someone has totally butchered it by soldering the inter board connector and other pieces of genius, it is possible that somehow the logic supply voltage is incorrectly connected and this could do all pre-drive transistors, but I would expect many more problem than just 2N4401s - out of interest have you run a meter over the power supply board?  I'd do this very early.)  Also do you know of the other WMS guides around www.pinball.flippers.info present an alternate view which may be beneficial.

On the resistors I wouldn't be too concerned about the seemingly out of spec measurements. From memory they are just pull ups / pull downs or used as current limiters for the C-E path.  If they were either open circuit or short circuit I'd be concerned, but yours are about right and for the range of other problems you seem to have I would not be fretting on them just yet.

For my problems I found it really beneficial to use a logic probe and examine the driving side logic and behaviour. With a jumper wire and power to the board (but not the solenoids - lift the solenoid fuse and maybe the connectors) you can step through and simulate every kind of driven condition, by this I mean special solenoid drive, solenoid test drive, drive from cpu and game over lock out. This gave me much clearer understanding of what was happening in the circuit. I sketched out a single leg of the drive for one solenoid and noted logic conditions and voltage etc. This dog eared piece of paper is in a log book and I'm happy to scan and flick it you way if you feel it may be of any use.

[robm]

Thanks heaps for the replys.

Tested the resistors out of circuit and they are spot one - great advice thanks retropin.

Firepower - that would be great if you could send me the 'logic diagram' (PM me if you want my direct email address if thats easier) - bought a logic probe today, so will search some tutorials on how to use this beast.  Unfortunately Jaycar didn't have the right molex connectors for the interboard, so will get some during the week and fix that first before powering it up to use the logic probe. 

[robm]

OK - i have replaced 3 x TIP122 transistors and as suggested - all the 2N4401's were OK when tested out of circuit.  A few resistors were also replaced.

I went and checked the resistance of all the coils - any that had a resistance lower than 2.5 ohms (suggested by pinrepair) i pulled completely out of circuit and tested again.

1 has zero resistance

1 has 1.6

1 has 2.3

Tested the diodes (out of circuit) and they are all OK

Should i replace all three of these coils? (Two of the  blown transistors were driving the 1st two coils listed above)?

Thanks

Rob

[beaky]

yep i would be replacing all 3 of those coils

[robm]

A bit of an update

I replaced all the female pins on the interconnector board

There are two main issues at this point in time.

1. No displays
2. Booting problems - i think...strange diagnostic 7 segment display on the CPU

1st the boot issues

About 1/2 the time, it boots seemingly OK (ie: flashes 0, then stays 0)
Other times it is a constant 0 (no flash), and sometimes error 2 comes up (bad IC13 RAM), once error 8 came up!!

Is there a way to test the RAM on the board (i have a logic probe but no idea what to do with it!!)? or should i trust the self test and just replace it?

Some of the other IC's are pretty dodgy looking (a bit of corrosion etc) but when i put the DMM on continuity, they were all getting a signal from the leg to where the socket is soldered on the PCB.


2nd the display issue

There is no power (a couple of mV) at the blanking signal wire (1J3 pin4) or test point 4 or interconnector pin 37.  I put +5V to TP4 and the displays started flashing some funky numbers on and off, so i think i can safely assume the displays are OK.  Twice when i powered it on a single 0 on one of the displays flashed up briefly.

Is this issue a result of the booting problems and the blanking signal is not allowing the displays to work, or am i completely on the wrong track?

Suggestions??

[ddstoys]

 2N4401 are just a signal transistor - generic replacements are at jaycar in the form of  PN100 or PN200...

This is handy to know Gav are there many other parts that can be substituded with parts from jaycar??  Could be a good 101 thread if i cant find the exact part numbers i think all is lost 

[shansta]

 2N4401 are just a signal transistor - generic replacements are at jaycar in the form of  PN100 or PN200...

This is handy to know Gav are there many other parts that can be substituded with parts from jaycar??  Could be a good 101 thread if i cant find the exact part numbers i think all is lost  

+1 please as I am an electronic idiot and Jaycar are bloody useless at finding substitutes! (But they are around the corner!)

BTW Rob - nice machine! One on my personal hit list (FP 1&2)