diagnosing and modifying timer circuit with op-amps

[Jbates58]

hi all,

the purpose of the timer is a glow plug controller for my diesel motor. it controls the glow relay turning the plugs on and off. it also controls an indicator light on the dash, and thats where my issue lies. i did think about by passing it and using a SPDT relay to trigger the LED, (easy as) but as the unit continues to cycle the glow plugs on and off after the motor has started, i dont want the light to keep comming on an off. it didnt do it in the original car and i dont want it to in the new one either.

long shot, but i am trying to adapt a timer into my car from my old car, and get it to work. i have nearly everything going, except the light on the dash. it pulses on for a split second and then its off. but the unit, as far as i can test & tell continues to operate correctly.

at first i though that it was because there may not be a limiting resistor on the  dash, been that the original was a fillament globe and the new one is LED, so i put in a 330 ohm and same results, so i tried the filament globe, and still the same result.

then i traced back the pcb a bit, and found that the ground lead of the led was connected to a d1698 transistor (on the collector pin), so i traced out the transistor, and the emiter pin runs to ground through a few possible options, but i measure no resistance between them.

looking at the base resistor, i thought that the value may be wrong for the led vs the fillament, so it played around with it using my decade box, and no go. (trying again with the fillamant globe also confirmed this). the base is controlled by a TA7590 IC (quad op-amp) and i am out of my league now. i looked into op-amps to work it out, but it still a bit past my current understanding.

i am hoping that there is someone on here, that lives in brisbane, australia, that has a good understanding on how op-amps work, that i can bring the unit to and can go through it with me. aswell as assist me in working out why its not working the way it should. (it worked correctly in the last vehicle, and as far as i can tell, all the wiring is correct [checked it a few times]).

i have attached pics of the pcb.

as far as i can tell, Q5 is the transistor that controls the LED, and its base resistor is R35. it is driven by pin 1 of the OP-AMP, and from there im out of my depth.

cheers

Jason




sorry, stupid sh1t a55 photobuchet wont let me rotate the pic.

[Andy Watson]

at first i though that it was because there may not be a limiting resistor on the  dash, been that the original was a fillament globe and the new one is LED, so i put in a 330 ohm and same results, so i tried the filament globe, and still the same result.

If you operated the unit without a resistor there is a chance that you will have blown the transistor. Do you have a schematic of the device?

[Jbates58]

at first i though that it was because there may not be a limiting resistor on the  dash, been that the original was a fillament globe and the new one is LED, so i put in a 330 ohm and same results, so i tried the filament globe, and still the same result.

If you operated the unit without a resistor there is a chance that you will have blown the transistor. Do you have a schematic of the device?

sorry no, i dont have a wiring diagram. and i didnt go to far below the resistor value (r35 [3.3K]) as i sisnt want to do any damage, i went as low as 3k.

Jason