So... that's the chip in my 80 box? I'm willing to just swap the chip out on my broke one and see what happens... so long as you guys agree that's the correct chip for my box.
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1980 Yamaha XS650 wiring and ground (-)
- Thread starter Dxs650
- Start date
sleddog83
XS650 Addict
The 83 version is the 12-03 module that uses a 20 pin chip. The board is similar in the input and output circuitry. The guts in the middle have been condensed down to fewer components. With fewer components they also reduced the need for a double sided board. The 12-03 and possibly the in-between version is a single sided board. You can still see some other similarities though in terms of the tantalum caps and paired resistors. I believe that in the later and final versions of this module they took the quad op amp IC and customized it by adding all of the extra components. Quite likely the modules had to be fine tuned with the paired resistors. They and the tantalum caps were not condensed into the customized IC. The board is essentially a analog computer that takes two input pulses, compares them and outputs a single output pulse to the coil. It is taking two pulses that are fixed in there timing as they always occur at the same degree before tdc(irrespective of the speed of the engine), applies some fixed timing as per the internal components, compares the result and outputs a variably timed(talking degrees before tdc). Of course this is still just my theory.
From a disconnected, yet curious observer, makes sense to me.
I wonder if it includes adaptive dwell...
I wonder if it includes adaptive dwell...
sleddog83
XS650 Addict
Jim,
Are you certain that the chip is bad? Like I have been trying to say, I think these may be common chips on the early versions but they are fine tuned with resistors. If you change the chip with out tuning it, It may or may not work. I believe all of the components on the 12-01 boards can be replaced, but I can't guarantee 100 % success if you did that. Best thing to do would be to put it on the bench, scope it to confirm the chip is bad and then replace only if necessary. If you want to send it to me, I'll take a look at it. I have some replacement ICs. One other thing to note about those boards. They are double-sided. Some of the circuit connections from one side to the other are through the eyelets. If you damage the eyelet when you desolder a component, you may break a connection from one side of the board to the other. I have a 12-01 board here. I haven't yet been able to confirm absolutely that it works. I could do a comparison between your board and mine, possibly even set it up the same.
The IC is just an educated guess. Starts easily and idles fine. On accel, it'll start sputtering and backfiring at about 2K. Downshifting to get the revs above 3000 and it'll run just fine. Let it get below that and the sputterin' returns until it gets below 2K then it runs fine again. Swapped boxes back and forth several times and the fail on this box is permanent and repeatable. My theory is that since it's the chip that builds the advance curve based on the retard and advance triggers.... it's the best starting point. My main curiosity is what's the odds on swapping it and the new one working with the boards current "tuning?"
I used to work flightline and backshop avionics so I'm comfortable swapping chips, but I don't have access to a scope to do any troubleshooting.
I used to work flightline and backshop avionics so I'm comfortable swapping chips, but I don't have access to a scope to do any troubleshooting.
Shotgunning electronics?
Sure, why not?
Whut do ya got to lose?
Can always put the old one back.
Unless you clipped its leads to get it outta there...
Sure, why not?
Whut do ya got to lose?
Can always put the old one back.
Unless you clipped its leads to get it outta there...
sleddog83
XS650 Addict
Sounds like nothing to lose.
sleddog83
XS650 Addict
Yah, I was trained in avionics but spent most of my career working on RADARs. What I wouldn’t give for now, for the parts bin and test equipment I had access to back then. Those ICs are at Mouser as LM2902N. They seem to be a direct replacement, but who knows? Worth a try, right. Let me know how it goes.
Jim, having a rethink here.
Sleddog83 has the electronics and bench experience,
He's already knee-deep into this reverse-engineering,
His schematics show Ansi and IEEE compliance,
He's got a dog in this hunt,
I'm strongly leaning to having you send him your TCI box.
Your box will add to his knowledge base.
Finding that the HA17902P may be directly interchangeable with the LM2902N opens up the door to realistic diagnostics, and maybe even a suitable replacement clone.
Thoughts on the tuned circuits. There's 2 types.
The original design - A section of the circuit may call for a specific resistance/wattage, only achievable (economically?) by pairing resistors. Production units will use these resistors, as supplied.
The tuned product - After partial assembly, the PCB is passed downstream to the configuration/tuning department. On the bench, with appropriate diag equipment, the tuners will add/tweak the final components to meet specs. Similar to the way early transistor radios used hand-wound inductors, the tuners squeezing/spreading the coils to fine-tune the IF sections.
If several of the TCI boards could be examined, and found to have identical component values, then there's a strong possibility that the suspected tuning is just the original design, not requiring follow-up bench tweaking...
Yeah... been thinking the same. He's in Canada, so shipping cost's are gonna suck. Guess I might just take one for the team here...
sleddog83
XS650 Addict
Whatever works for you. My TCI projects are actually somewhere down on my list of things to do. I am currently trying to finish my garage and workshop. I pick at the TCI piecemeal, when it is really rainy or when I am too lazy to do anything else. I couldn’t guarantee a fast turn-around for you. I was thinking about the description of the fault, and I am thinking that the IC may not be the problem. I think if anyone of those op amps was bad, it wouldn’t work at all or the timing would be completely off. More likely it is a cap that has failed, failed resistor or solder that has gone punky somewhere. You could try resoldering the whole board. It would be interesting to compare boards. I wish I had a Huntron Tracker.
Well if you're interested in, as 2M said, adding to the knowledge base... I'll send it to you. No sign of overheating or damage on the caps or resistors (or any component for that matter). Not definitive I know, and I looked it over pretty good for bad solder joints. After all I read here about the crappy solder jobs on the boxes I was surprised to find these are actually pretty good. Riding seasons about over here so no rush. Keep it all winter. PM me your address and I'll get it to you in the next week or two.
sleddog83
XS650 Addict
Jim,
Having trouble figuring out how to send a message.
Having trouble figuring out how to send a message.
Top right on the title bar... "Inbox". Hover over that and you'll see "Start New Conversation" Click on that, type in my name... title.. message.
Your best bet is to start a thread in the garage with a good DESCRIPTIVE title, and as much information about the issue AND the bike with pictures in your post. ALL of us are better than ANY of us at problem solving.
Top of the page. Click Forums
Click on "Garage."
Scroll down. On the right side you'll see "New Thread." click it.
And there ya be.
