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Djet computer fixable? 140-160 1972

posted by  someone claiming to be Niel on  Tue Jul 29 09:33 CST 2003 [RELATED]

Found the schematic some time ago on the net:
http://members.rennlist.com/pbanders/ecu1.jpg

Check for 12 Ohm resistance between pins 3 & 9 and between pins 5 & 7. I'll bet one of those 5W resistors are either burnt out of has a broken solder joint. A 6 Ohm 5W resistor is rated for 5.5V average, and in D-Jet it is energised 50% of the time (T251 does the inversion between the 2 banks). If an injetor or an ECU output is short circuit to GND, the injector resistor will average 50% of the supply voltage (ignoring D502 voltage drop). At 13V supply, the resistor would see 6.5V and dissipate 7W. Would not last long in that state.

Solder joints get weak from heat cycling, and form intermetalic compounds: perfectly conductive, just very brittle. This is the infamous relay solder joins problem assosiated with newer models, and usually occurs after about 10 years. OD and fuel pump relays are famous for this, because they are energised most of the time (heating up).

niel at volvoadventures dot com






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