JIMSTIM 1.5 build

[slomo85]

Hello all! I just finished building my jimstim 1.5 and all the leds tested good, but when I do the tach test I get nothing... So I checked all the voltages on the board with a multimeter using the pin headers... here is what I read:

3.3v = 2.9v
12v = 7.03v
5V = 0v

Nothing gets hot even after leaving it on for an hour...

Oh no, what did I forget/break?

[Peter Florance]

Hello all! I just finished building my jimstim 1.5 and all the leds tested good, but when I do the tach test I get nothing... So I checked all the voltages on the board with a multimeter using the pin headers... here is what I read:

3.3v = 2.9v
12v = 7.03v
5V = 0v

Nothing gets hot even after leaving it on for an hour...

Oh no, what did I forget/break?

The 5v is supplied by a connected MS box (Vref) IIRC
Do you have one plugged in?

[racingmini_mtl]

Peter is correct about the 5V being supplied by the MS.

The 2.9V you get is lower than it should. Can you check the voltage again with the CPU removed? Also, check the voltage on the CPU socket: you should get 3.3V on pins 1 and 3.

Jean

[slomo85]

Ohh, it's not hooked up to the megasquirt... I wanna get the stim working properly before I try that...

The power supply is a walwart supplying the jimstim with 9vdc 200mA. That may be a problem lol! My bad... Ok, just cut up another walwart supplying 12vdc 600mA and my voltages are a little higher at:
3.3V = 3.007
12v = 9.82
5v still nada... This is because it's not hooked up to anything right?

Using "http://www.kpsec.freeuk.com/components/ic.htm" as a ref for the pin locations I followed "Troubleshooting tach signal, CPU and 3.3V" at "http://jbperf.com/JimStim/JimStim_v1_4_assembly.html" and found the following:

pin1 and pin3 have voltage, pin 13 and 14 do have voltage that varies with the fine and course pots... so that all checks out good... I also just desoldered a few "shoddy" looking joints and used my good paste(just got it) to solder them again and they look real good now! But it still doesn't work no changes...U think the regulator is bad since the 12v is so low? It doesn't even hardly get warm...

Edit: Just tried this... Using the middle pin as a ground ref on the regulator, one pin reads 3.055v and the other 9.91. This is measuring at the regulator itself. Checking the voltage into the jimstim is 10.63v. I dunno... if i can't build this thing how am I ever gonna build the megasquirt?! ...

[Peter Florance]

Ohh, it's not hooked up to the megasquirt... I wanna get the stim working properly before I try that...

The power supply is a walwart supplying the jimstim with 9vdc 200mA. That may be a problem lol! My bad... Ok, just cut up another walwart supplying 12vdc 600mA and my voltages are a little higher at:
3.3V = 3.007
12v = 9.82
5v still nada... This is because it's not hooked up to anything right?

Using "http://www.kpsec.freeuk.com/components/ic.htm" as a ref for the pin locations I followed "Troubleshooting tach signal, CPU and 3.3V" at "http://jbperf.com/JimStim/JimStim_v1_4_assembly.html" and found the following:

pin1 and pin3 have voltage, pin 13 and 14 do have voltage that varies with the fine and course pots... so that all checks out good... I also just desoldered a few "shoddy" looking joints and used my good paste(just got it) to solder them again and they look real good now! But it still doesn't work no changes...U think the regulator is bad since the 12v is so low? It doesn't even hardly get warm...

Edit: Just tried this... Using the middle pin as a ground ref on the regulator, one pin reads 3.055v and the other 9.91. This is measuring at the regulator itself. Checking the voltage into the jimstim is 10.63v. I dunno... if i can't build this thing how am I ever gonna build the megasquirt?! ...

12v is the source from your wallwart.
Did you remove the CPU chip like Jean suggested?

[racingmini_mtl]

The difference between the voltage coming in and what you see at the regulator is normal because there is a diode in between which will account for the 0.7V drop. And having 10.63V from a wall wart rated at 12V is not surprising.

What is surprising is that you only get 3V out of the regulator. That's why I asked to re-check without the CPU (or was this without the CPU?). If you get more voltaeg without the CPU then there might be an issue. Also check to see if D4 or F1 is getting warm.

And as mentioned, you will not get 5V until connected to your MS.

Jean

[slomo85]

I only checked the voltages with the chip in, all I checked with it out were the 4 pins... the voltages were consistant with the 3v I had been seeing on the 3.3v headers... I will check again right now just to clarify:

Chip out:
3.3v = 3.045
12v = 9.84

Chip in:
3.3v = 2.981
12v = 9.80

Power outta the wallwart while not hooked up to anything is: 12.25v
While hooked up to the stim: 10.7v (prob because of the stim's draw right?)

D4 and f1 do not feel warm at all... Measuring voltage across D1 is: 3.004v and f1 is: .019v

Any other ideas??

[slomo85]

What is surprising is that you only get 3V out of the regulator. That's why I asked to re-check without the CPU (or was this without the CPU?). If you get more voltaeg without the CPU then there might be an issue. Also check to see if D4 or F1 is getting warm.

Since the difference is so small is it still surprising? In either case, what component would this most likely relate to?

Edit: I'm loosing my electronics skills! lol! measuring the voltage drop of a component ... U want that low correct? Like F1 showing such a low voltage, meaning it has almost no voltage drop since it's operating correctly. Since D4 is showing such a large voltage drop it means it's most likely open, correct? Or is my memory just completely hosed?

[slomo85]

Any ideas???

[Peter Florance]

What is surprising is that you only get 3V out of the regulator. That's why I asked to re-check without the CPU (or was this without the CPU?). If you get more voltaeg without the CPU then there might be an issue. Also check to see if D4 or F1 is getting warm.

Since the difference is so small is it still surprising? In either case, what component would this most likely relate to?

Edit: I'm loosing my electronics skills! lol! measuring the voltage drop of a component ... U want that low correct? Like F1 showing such a low voltage, meaning it has almost no voltage drop since it's operating correctly. Since D4 is showing such a large voltage drop it means it's most likely open, correct? Or is my memory just completely hosed?

D4 is reverse biased in this case so, no it won't be .6 v

[slomo85]

I just need to get this working so that I may continue building the squirt... I'm just confused as to what part is bad... I can measure anything, u peeps have any ideas?

[slomo85]

so... bueller?

[slomo85]

I took a look at the 1.4 schematic and started backtracking... Looking at the bias of Q1 (middle leg) I see no .6v... that's what u need to forward bias correct? So I move onto R21 and I see no voltage into it. So then I look at pin 15 of teh cpu and it's zero. These reading all taken with the rpm pots all the way up! pins 13 and 14 are still getting the voltage applied by the pots, still varies when they are turned... The voltage into the CPU at pins 1 and 3 is good... the spare is making the leds light to... maybe just this part of the chip is broken? I think I'm going to try a new cpu, but I hope it's good after that... I would hate to have not checked something else simple and ordered that part to at the same time

[racingmini_mtl]

What you could try to see if the issue is really the CPU is to remove the CPU and configure the JimStim as per the instructions for testing the tach signal. Then apply 3.3V (using a wire jumper from the 3.3V header or from pin 3 of the CPU socket) to pin 15 of the CPU socket. Each time you apply the voltage, you should see the LED light up. If that's the case then there is likely an issue with the CPU. If you don't see the LED light up then one of the components has failed or there is a bad solder joint.

You also want to check that the DIP switches are working properly otherwise you won't get the correct wheel pattern or may even get no pattern. Check that each switch connects the corresponding CPU socket pin to ground when the switch is on. The only exception is switch #1 (connected to pin 11) which should always stay floating.

Jean

[slomo85]

I tried that last night before I went to bed... the LED lit up!

I'll check the dip switches again before putting the new cpu in as well, thanks for the tip

[slomo85]

Well I finally got the new chip in the mail today, taking ESD precautions this time just in case It's still not working, in fact, everything is absolutely the same as it was with the old cpu! I gotta find out what's wrong with this thing... this mega squirt cost me a real grip and I can't even build the stim?!! ...

[slomo85]

I just don't get it... If anyone can help me at all I would appreciate it soo much! I have a multimeter and I'll do whatever you say! I have been looking over the v1.4 schematic forever now!

[slomo85]

WOW, so now I'm even more confused!! Just checked r21 and still no voltage to forward bias q1... but checked r22 and there's 8.7 volts! The schematic just shows this going to the pull up pin header!! Where is this voltage coming from!!????!!!?

[racingmini_mtl]

Do you have the pull up jumper installed in the 12V position? If so then it's normal that you get that kind of voltage. If you don't have a jumper then you need to check the solder joint on the header. Also, check the board if there could be any fault around there.

Jean

[slomo85]

Well, I fixed it... Even though the walwart PS i was using was within the acceptable range for use with this board, after using a larger one all my problems went away. I am now using an ols sega genesis walwart with an output of 9vdc 1.2 a... Guess they knew how to make them back then lol! Measured voltages now read:

12v = 11.74v
3.3v = 3.28v

Thanks for the help, Finally getting the light to flash makes me feel so good right now, even as lame as that sounds...

BTW, no, pullups were all removed as per the instructions for the test