novacaine
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| posted on 2/9/08 at 03:52 PM |
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megasquirt mega-pain-in-the-arse
Further to this thread
I have now received my "sample" MAX232CPE IC's (i ordered 3 in case i break one  )
I’ve now fitted them, and guess what?
I Still can't get connectivity.
I’ve tried Hyperterminal and Tera Term and neither give a response on the loopback test.
I've also gone ahead and soldered the timing circuit on and installed the processor and megatune cant detect the processor so it definitely
isn’t connected 
so where do I got from here?
I'm getting rather fed up of it ,
I've pulled up the circuit diagram of megasquirt and I’ve gone through with the multimeter to make sure that the IC is properly connected to the
capacitors, and they are, when the circuit is on, i can measure the voltage across the caps, i assume this means that they are working ok, i've
made sure that there is continuity between the MAX232 and the processor pins 12 &13, and that there is continuity between pin 15 of max232 and the
central pin of the voltage regulator and there is 4.95V over pins 15 & 16
I'm stuck, i really cant see what is wrong with it, the cable is a straight through cable, i've tried connecting with two different
PC's
any help greatly appreciated
Matt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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mr henderson
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| posted on 2/9/08 at 03:58 PM |
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Can't help, I'm afraid, just wanted to comment that everytime I read sommething about Megasquirt it seems to be something bad.
Presumably people don't post when everything works just fine?
John
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novacaine
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| posted on 2/9/08 at 04:05 PM |
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quote:
Originally posted by mr henderson
Presumably people don't post when everything works just fine?
You're Probably right,
if i can get the damn thing working i'll be well chuffed, mind you, quite a few of the "first engine start" only mention megasquirt
as a side line, there are a few sucess stories out there (im hoping )
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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martyn_16v
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| posted on 2/9/08 at 04:10 PM |
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quote:
Originally posted by mr henderson
Presumably people don't post when everything works just fine?
That's the way of the world 
So i'll break the trend. The MK will be the fourth engine I've 'squirted, and I've never had a problem. One of them was the
daily driver, the Mrs used it to commute to work for a whole winter with no problems, and if she can't break it then no one can (she's a
serial car wrecker )
Have you checked continuity all the way from the MAX232 pins to the pins on the DB9 connector (to see if you've got a broken track or dry joint
on the PCB)?
Saying that, if you can't even get a result on the cable loopback test then it's not the MS that's at fault. If you've done it
on two different PC's then it'd have to be the cable...
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novacaine
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| posted on 2/9/08 at 04:28 PM |
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ahh pin 13 (U6) ---> Pin 3 (DB9) no PD, No continuity when tested for resistance
same story with 14 > 2
solder joints look fine, what should i do?
would it be ok to solder a jumper wire ?
Thanks
Matt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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martyn_16v
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| posted on 2/9/08 at 04:34 PM |
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Try and follow the tracks along the board to see if there are any obvious breaks. Bit odd for them both to have gone though. Soldering jumper wires
across to test is fine, it'll help to confirm the problem at least.
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novacaine
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| posted on 2/9/08 at 04:42 PM |
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13 > 3 was not broken my mistake, but 2>14 was indeed broken, i've put a jumper across but still no joy
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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MikeRJ
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| posted on 2/9/08 at 04:44 PM |
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quote:
Originally posted by novacaine
ahh pin 13 (U6) ---> Pin 3 (DB9) no PD, No continuity when tested for resistance
same story with 14 > 2
solder joints look fine, what should i do?
would it be ok to solder a jumper wire ?
You could just put some jumpers on, but I'd want to know why there's no continuity. If you've got a shoddy PCB then how many other
problems is it going to have?
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novacaine
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| posted on 2/9/08 at 05:31 PM |
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arrgh, neither 13 > 3 or 14 > 4 were broken, im starting to get frustrated with the multimeter
So here is a summary of points
1) Straight through cable
2)Full connectivity to the DB9 Connector
3)Full connectivity to the C26-29 capacitors
3)Full connectivity to the processor (pins 12 &13)
4) There is 5v across pins 15 & 16 (U6)
The only thing i haven’t done yet is to attach the ally heat sink, would this make a difference (maybe the voltage regulator is grounded this way?
i do appreciate your help guys
i will crack this
Matt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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iank
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| posted on 2/9/08 at 05:47 PM |
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If there's 5v on the board then the regulator is fine.
Couple of things:
Are the capacitors round the right way? IIRC they are large enough to be polarised for the MAX232
Which COM port are you using on the PC? Are you sure it's the one you've connected the serial cable to?
Is the COM port a built in one or a USB<->Serial converter?
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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novacaine
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| posted on 2/9/08 at 05:59 PM |
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quote:
Originally posted by iank
Couple of things:
Are the capacitors round the right way? IIRC they are large enough to be polarised for the MAX232
The ones i ordered are tiny ( i used the digikey BOM so i used the part Numbers as suggested)
quote:
Originally posted by iank
Which COM port are you using on the PC? Are you sure it's the one you've connected the serial cable to?
I've checked that, device manager shows which COM port is in use
quote:
Originally posted by iank
Is the COM port a built in one or a USB<->Serial converter?
Both, i've used a USB Converter on my laptop and the built in one on my desktop no joy on either
The PCB shows no indication of polarisation of the caps, (V3) but i'll double check the part numbers never the less
thanks
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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MikeRJ
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| posted on 2/9/08 at 06:01 PM |
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Have you measured the voltages on pins 2 and 6 of the MAX232? They should be +10v and -10v respectively.
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novacaine
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| posted on 2/9/08 at 06:31 PM |
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-2.6 on pin 6 and 5.8 on pin 2, i've changed the IC's and got the same result
(that is with the Serial Cable connected)
If i remove the cable and leave the stim in it reads +10 and -10
is that normal?
(as you can guess by now i'm not exactly the most knowledgeable on electronics)
thanks for your help
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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martyn_16v
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| posted on 2/9/08 at 06:38 PM |
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OK, don't shoot me but... Is the MAX232 chip in the right way round in the socket?
Does the loopback test work when you're just testing the cable? If so, are you seeing two of everything you type in, or just one?
If you just see one of each character when you type, what happens if you unplug the cable and carry on, do you still see characters as you type?
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novacaine
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| posted on 2/9/08 at 06:57 PM |
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jumping pins 2 & 3 on the cable work with the loopback test (only echoed once per key stroke)
if i take the jumper out and try it then no characters are echoed
Max232 is in the right way round (to be fair that was a sensible suggestion, that’s the kind of thing i would end up doing )
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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MikeRJ
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| posted on 2/9/08 at 07:04 PM |
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quote:
Originally posted by novacaine
-2.6 on pin 6 and 5.8 on pin 2, i've changed the IC's and got the same result
(that is with the Serial Cable connected)
If i remove the cable and leave the stim in it reads +10 and -10
is that normal?
Not really...it suggests something is loading down the -10v charge pump, which in turn is loading down the +10v pump. They do tend a sag a little bit
when you have a PC connected but not that much IME.
Could you measure the voltage on pins 14 and 7 of the MAX232 with the cable connected and unconnected?
Just to check, the DB9 serial connector on the MS PCB is definitely a female one, i.e. sockets rather than pins?
EDIT: do you have 0.1uF or 1uF capacitors for C26-C29? The MAX232 should use 1uF, the MAX202 or MAX232A should have 0.1uF. I'm fairly sure the
MS bill of materials calls up the MAX232A or one of it's clones.
[Edited on 2/9/08 by MikeRJ]
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novacaine
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| posted on 2/9/08 at 07:19 PM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by novacaine
-2.6 on pin 6 and 5.8 on pin 2, i've changed the IC's and got the same result
(that is with the Serial Cable connected)
If i remove the cable and leave the stim in it reads +10 and -10
is that normal?
Not really...it suggests something is loading down the -10v charge pump, which in turn is loading down the +10v pump. They do tend a sag a little bit
when you have a PC connected but not that much IME.
Could you measure the voltage on pins 14 and 7 of the MAX232 with the cable connected and unconnected?
Just to check, the DB9 serial connector on the MS PCB is definitely a female one, i.e. sockets rather than pins?
[Edited on 2/9/08 by MikeRJ]
The DB9 on MS board is male
could this be the major duh moment?
That would mean that the pins are all the wrong way around
::embarrassed ::
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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novacaine
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| posted on 2/9/08 at 07:24 PM |
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i never even thought about that, the digikey part number was obsolete so i just ordered a connector not thinking
time to get the desolder pump out
Just a though though, will i have destroyed the IC's, i have also connected the processor up, will any damage have occured to that?
not too bothered about the IC's as they are cheap, the processor on the other hand isnt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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paulf
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| posted on 2/9/08 at 07:45 PM |
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I would leave the male socket on the board and just rewire the serial cable to connect the same as a female version, Ie reverse the connections, use
the board and circuit diagram to confirm.
The processor should be ok, you are more likely to do damage unsoldering the socket.
Paul.
quote:
Originally posted by novacaine
i never even thought about that, the digikey part number was obsolete so i just ordered a connector not thinking
time to get the desolder pump out
Just a though though, will i have destroyed the IC's, i have also connected the processor up, will any damage have occured to that?
not too bothered about the IC's as they are cheap, the processor on the other hand isnt
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MikeRJ
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| posted on 2/9/08 at 08:14 PM |
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I'd change it personaly, as otherwise it means you need a special serial cable which you are guaranteed to lose. The MS uses the hardware
handshaking lines as well so it's not just TX,RX and ground to change.
I doubt you have damaged the processor, RS232 signals have a fairly low current limit. At least you've found the problem.
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novacaine
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| posted on 2/9/08 at 08:21 PM |
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Thanks everyone for your help, without you lot I would never had fixed this one
thanks
Matt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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