i fixed one once it needed all of the dusty stuff taking out
some long pins that were arcing to the case snipped off
and i went over bits that looked suspect with the soldering iron, no idication of dry joints but it looked over heated so i melted and remade any joint that looked suss.
this was a 6al from the 80s or 90s it had the hole in the side for the rev limiter pill and a plug in wire connector for a long obsolete retard unit.
these units look to have been hand soldered with mainly discrete components by a skilled worker rather than a robot. all components labelled
there is not a lot to go wrong and provided the coil and capacitors in the vibrator circuit and the big transistors are ok the rest is about 10 quids worth of RS components.
looks like this
if it whistles or buzzs there ain't much wrong
i failed to fix one from Duncan it was a modern big fat one MSD really don't want you in there, and they have made it very hard to fix anything other than the fusible links on the board ( 1/4 inch long wires in a braided wrap near where the power cables connect)
it is machine soldered and they have gone to some length to remove the markings on the major components
the units has 100s of sub miniature components all approx 1.5mm long by 0.75 mm wide with no markings and has been heavily lacquered making removal and future soldering really hard. i.e the labelling of these components was on the big long plastic clip they were loaded into the machine from, the chances of hand soldering are reduced. and the lacquer on the board makes point to point fault finding with a meter nigh on impossible.
you could remove the lacquer but you can't do that with thinners if there are wound components still on the board as the thinners will damage them
I still have duncans and when i'm feeling at a loss for what to do i have another go at it but i have made little progress....
HEI
if you do not need
1) Rev Limiter
2) Launch Control
3) Ignition Retard for starting or other
4) 7000+ rpm operation
AND
1) have a magnetic trigger distributor that you like with a curve you like. its a 4 wire hookup operation
and bypass your ballast
buy a $20 4 pin HEI and a £25 DLB198 coil and you have the same ignition set up used on 6 and 12 cylinder jaguars
Just your $20 HEI module is nude, exposed, and looks like a wonky computer chip and the one in the Jag comes in a big Jag branded case and costs jaguar prices
4 pin HEI modules used by GM and any company that once had a relationship with GM or their OEM suppliers.
that's just about everyone at some point in the 70s and 80s.....its been well tested and is based on a motorola design
most magnetic pickup module based ignitions use a motorola chip designed in the 70s doesn't matter who makes the module. same gubbins inside
If you want to try to fix your MSD
http://holdenpaedia.oldholden.com/MSD_6AL
will give you the full run down
if it looks like the picture you have a fighting chance
take off the base
take out board
look for burny bits loose bits arching
resistance of resistors should be as per the bands
fuses should have continuity
diodes have massive resistance 1 way and next to nothing the other
if you measure the resistance of a capacitor it should increase from 0 to infinite. if it doesn't don't hang about swap the leads over and check you didn't overheat it and make it bulge
capacitors metal tops should not bulge
capacitors sides should not bulge
if the unit is full of fluff tin foil or white plastic gunk look for the exploded capacitor and replace
if you measure the resistance between middle and outer legs of a transistor style package in most cases it behaves like 2 diodes connected back to back
coils should have continuity on primary and secondary side.
check the fusible links first
dave