Circuit Board

[danforth]

I can't understand why jumpstarting caused the burnup either as the parallel connection still only equals the input voltage, the current being drawn dictated by the circuit until the vdr went low. I have seen far worse damage with a vdr/fuse combination where both have been obliterated but these were due to lightning strikes

I wondered about that as well, maybe jump started with 24v? Don't know much about farm equipment except it can be a bit "industrial".
Can't help feeling it's another case of electronics gone mad. A useless tractor because some minor part of a pcb is "nit picking".

 

[dazling]

I don't know why it went and im only relaying what my mate said that he jumped it whilst the lights was on
and he shouldn't off, he could of 24v it to start I don't know will ask more details
I think its a bit too fiderly for me to do was hoping it would be just a diode that needed changing lol

 

[danforth]

I don't know why it went and im only relaying what my mate said that he jumped it whilst the lights was on
and he shouldn't off, he could of 24v it to start I don't know will ask more details
I think its a bit too fiderly for me to do was hoping it would be just a diode that needed changing lol

Don't give up hope M8, plenty of help on here! If you can handle a small tipped soldering iron and a multimeter, you'll be fine,
assuming what we can see is the only damage. Follow chookey's advice, and then mine about the fly leads as a temp measure.

May need guesswork with the "varistor" if it's duff, but the "frazzler" is not too complicated, can be roughly found by experiment.
Once you know what works, it can be fixed using epoxy to a convenient part of the pcb and wired to suit. Crude, but should work,
a more professional repair needs more skill, but won't work any better.

And, if you don't have much experience, just post the pcb to me. PM me if you want. No charge, and not a lot to lose.

 

[dazling]

And, if you don't have much experience, just post the pcb to me. PM me if you want. No charge, and not a lot to lose.

Thanks m8ty I might just take you up on that

 

[Spectre]

Don't give up hope M8, plenty of help on here! If you can handle a small tipped soldering iron and a multimeter, you'll be fine,
assuming what we can see is the only damage. Follow chookey's advice, and then mine about the fly leads as a temp measure.

May need guesswork with the "varistor" if it's duff, but the "frazzler" is not too complicated, can be roughly found by experiment.
Once you know what works, it can be fixed using epoxy to a convenient part of the pcb and wired to suit. Crude, but should work,
a more professional repair needs more skill, but won't work any better.

And, if you don't have much experience, just post the pcb to me. PM me if you want. No charge, and not a lot to lose.

If the other thing is a varistor we need to know the voltage supplied to the board. Select one with some headroom but not too much. Putting one in with a high Joule rating won't matter.

 

[parker13]

My thoughts are the varistor is probably there as a safety device, designed to go open during a surge and may well be the only component that needs replacing,

 

[danforth]

My thoughts are the varistor is probably there as a safety device, designed to go open during a surge and may well be the only component that needs replacing,

I'd guess the burnt ruins might need something in there.:Biggrin2:

 

[parker13]

The only BURNT RUINS appear to be some copper track, that can be bridged, to be more accurate a knowledge of Electrical Engineering and a Multi Meter would be needed.........

 

[danforth]

The only BURNT RUINS appear to be some copper track, that can be bridged, to be more accurate a knowledge of Electrical Engineering and a Multi Meter would be needed.........

If you look at the original pic in post#1, that's the burnt component I was talking about.

The later pic in post#16 (bottom one) shows the track after the component was removed (that's what I meant about "burnt ruins", perhaps a bad description)

Anyway, it only had 2 pins, shouldn't be too difficult to guess what it was and, as you say, could probably be fused or bridged, at least for test.

 

[parker13]

If a blown component that's totally blown that's tricky, could be diode or resistor, would need the circuit or chip info to possibly work it out, either way it's getting tricky.

 

[Spectre]

I don't suppose you can see where the polarity band is on the "diode" @dazling?

I was just thinking, sometimes zener diodes are used to clamp supplies so it may be in parallel with the supply (reverse bias) rather than in series as would a polarity protection one which probably aren't as common on boards with keyed connectors etc.

Need to find out what frazzled component was doing somehow.

 

[danforth]

I don't suppose you can see where the polarity band is on the "diode" @[URL="http://www.digitalworldz.co.uk/members/dazling.html?quot;=]dazling[/URL]?

I was just thinking, sometimes zener diodes are used to clamp supplies so it may be in parallel with the supply (reverse bias) rather than in series as would a polarity protection one which probably aren't as common on boards with keyed connectors etc.

Need to find out what frazzled component was doing somehow.

I believe the pcb is going to be posted to me. It'll make more sense when I check the track layout, even without a schematic.

I'll keep you posted, remote diagnosis from pics has it's limitations. The main concern is any collateral damage we can't see.

Not saying I won't be back for suggestions though!

 

[Spectre]

I believe the pcb is going to be posted to me. It'll make more sense when I check the track layout, even without a schematic.

I'll keep you posted, remote diagnosis from pics has it's limitations. The main concern is any collateral damage we can't see.

Not saying I won't be back for suggestions though!

I look forward to the complete reverse engineered schematic .

Anyone got the connector pinout?

 

[danforth]

I look forward to the complete reverse engineered schematic .

Anyone got the connector pinout?

I came across wiring diagrams when looking for a schematic, didn't take much notice at the time.

Looks like I will now!:Biggrin2:

 

[dazling]

will be in the post today danforth many thanks

 

[danforth]

@little_pob

Not sure about this thread in here. It's a specific problem from one member, and not a general hobby subject.

TBH, I don't know where it should be either, but pcbs are in pretty much any hardware on DW.

But you wouldn't put say, a Dreambox psu pcb in here? Yeah, I know, it's off a tractor

The "Electronics" thread is OK, it's general reminiscing really.

 

[little_pob]

@little_pob

Not sure about this thread in here. It's a specific problem from one member, and not a general hobby subject.

TBH, I don't know where it should be either, but pcbs are in pretty much any hardware on DW.

But you wouldn't put say, a Dreambox psu pcb in here? Yeah, I know, it's off a tractor

The "Electronics" thread is OK, it's general reminiscing really.

Slip of the finger following moving some others, should have gone in car and van...

 

[danforth]

Got my hands on it now.:Biggrin2: Some progress, the VDR is s/c, measures 7 ohms (off pcb).

It has X1429 671S (S could be a 5) etched on it in tiny letters......Anyone identify?

Printed over that is what looks like 7491 (larger and upside down). Not certain about the 91 (charred)..... I can't identify it......Anyone else?

The supply is 12v (confirmed by dazling) via the "frazzler", which does have a band on one end, now o/c. (diode?)

The one above the "frazzler" was detached from the pcb at one end (see pics from dazling) . Removed from pcb for easier access to
repair the tracks. That one also has a band, and tests like a diode (think it's marked 6G 7A, can't identify that either).
Not too bothered about that one, can reconnect.

The "frazzler" feeds two LM 2931AT-5 voltage regs (5V o/p) the first one direct, and the second via the detached diode above.
I'll post a diagram of cct area (if needed) when I get time to draw one.

If I bypass the "frazzler" with 12v (VDR off pcb) I get a 5V o/p from each, as expected.

A guess for the VDR (about 2cm diameter), if it can't be identified, and assuming 14-15v from an alternator.
Caps across VDR and regs are 35v. Reg i/p is 40v max continuous, 60v transient.

Reg spec here. View attachment LM2931AT-5.pdf

So, guess about 20v.....Make sense? Also thinking 1N4148 for "frazzler"? (smd pads are shot anyway).

 

[Spectre]

Got my hands on it now.:Biggrin2: Some progress, the VDR is s/c, measures 7 ohms (off pcb).

It has X1429 671S (S could be a 5) etched on it in tiny letters......Anyone identify?

Printed over that is what looks like 7491 (larger and upside down). Not certain about the 91 (charred)..... I can't identify it......Anyone else?

The supply is 12v (confirmed by dazling) via the "frazzler", which does have a band on one end, now o/c. (diode?)

The one above the "frazzler" was detached from the pcb at one end (see pics from dazling) . Removed from pcb for easier access to
repair the tracks. That one also has a band, and tests like a diode (think it's marked 6G 7A, can't identify that either).
Not too bothered about that one, can reconnect.

The "frazzler" feeds two LM 2931AT-5 voltage regs (5V o/p) the first one direct, and the second via the detached diode above.
I'll post a diagram of cct area (if needed) when I get time to draw one.

If I bypass the "frazzler" with 12v (VDR off pcb) I get a 5V o/p from each, as expected.

A guess for the VDR (about 2cm diameter), if it can't be identified, and assuming 14-15v from an alternator.
Caps across VDR and regs are 35v. Reg i/p is 40v max continuous, 60v transient.

Reg spec here. View attachment 80031

So, guess about 20v.....Make sense? Also thinking 1N4148 for "frazzler"? (smd pads are shot anyway).

1N4148 is a small signal diode, I'd get something bigger, in that package size which is possibly SMB. Are there any bulbs or anything hanging off those regulators?

Your Search Results | Farnell UK | Results

As for the varistor, you could guess somewhere in the 20V~30V range maybe but the battery voltage jumps up whenever loads are shed. Meaning that if you pick one with too low a clamping voltage then it will operate more frequently and go bang quicker. Sometimes they have their rating on them in the part code but the one you posted isn't like something I've seen before. Maybe it's an automotive one can you post a picture?

You can guess the rating from the size but 20mm starts at 36V:

Your Search Results | Farnell UK | Results

 

[danforth]

1N4148 is a small signal diode, I'd get something bigger, in that package size which is possibly SMB. Are there any bulbs or anything hanging off those regulators?

Needs to be wire ended, surface mount pads have burnt away. Physically not much bigger than a 1N4148 (got plenty of others with higher rating).
Reg i/p draws 2.5ma on first, and 36ma on second. Think max rating for each is 100ma o/p (not clear from spec, says "in excess of 100ma", but no max quoted.
Not checked reg o/p circuitry yet, but without harness plugs connected, can't guess at working load. Will check for pcb bulbs, but if 100ma is max?

As for the varistor, you could guess somewhere in the 20V~30V range maybe but the battery voltage jumps up whenever loads are shed. Meaning that if you pick one with too low a clamping voltage then it will operate more frequently and go bang quicker. Sometimes they have their rating on them in the part code but the one you posted isn't like something I've seen before. Maybe it's an automotive one can you post a picture?

You can guess the rating from the size but 20mm starts at 36V:

36v ok for regs, but pushing it for 35v caps, tractor pcb from 1998, modern lower voltage VDRs may be physically smaller?

Will try to post a pic, but the light angle is critical to read anything much.

Edit:-Can't get useful hi res pic.