Agilent 6890N GC hardware problem

[queenann]

Hello All,

My Agilent 6890N GC is currently non-functioning. It originally started with an oven error. After a run during oven cool-down, the instrument would shut down because it could not cool down. The oven flapper would not open to vent out the hot air. Sounded like an easy fix initially. Just change out the motor.

The oven flapper motor was replaced with two different motors and still would not move. No grinding sound at all.

The main mother board was suspected and that was replaced with a brand new one. Less than a minute after it was powered up, a chip literally blew off. Upon closer inspection of the original board, the chip in the same location was dimpled.

The person who was doing the repairs was berated for not changing out the AC power board before replacing the mother board. Both were replaced, the oven was powered on, and the chip on the mother board burst into flames. The chip was okay when turning on the inlet temp, flows, and detector temps, but not when the oven temp was turned on.

Besides the sad fact that the fuses on both the mother board and the AC power board are useless, what could be causing this?

The universal transformer? Triac?

[gcmol]

Phone agilent!

[queenann]

Phoned in agilent this morning. Was just as vague with "static discharge" and "loose connection" suggested as a reason for the fuses not working.

Normally there are 4 reasons for "the oven not working".

Oven Flapper motor
Main Board
AC Power Board
Oven Heat Shroud

Three of the reasons were ruled out by installation of new parts. The fourth doesn't make any sense given that the oven was heating up when my original main board was in.

[Peter Apps]

This really really needs someone with the electrical and electronic skills to do systematic troubleshooting - electricity can get dangerous so proceed at your own risk. Blowing up motherboards is an expensive test procedure, so I think that you need to go to offline tests. First thing is to check that the wiring insulation is intact, because short to the chassis could certainly cause the problem.Depending on motor type, if the flap itself is jammed, rather than the motor itself being faulty, then the motor will draw extra current which might blow a chip. Since you do not have a functioning motherboard now, try removing the motor and moving the flap by hand. If it moves freely check the motor contacts on any of the motors that you have for continuity. If there is a circuit it might be a short circuit - there should be some resistance - sorry I've no idea how much. If you have a resistance then apply voltage - there might be a plate on the motor with specs, or a serial number that you can google. If the motor spins and the flap moves you probably do have a board error. Good luck.

Peter

[gcguy]

This problem would appear to require some very specialised testing and repair equipment. This might do the trick.

http://en.wikipedia.org/wiki/File:Roadroller.jpg

[queenann]

It ended up that the cause of all this was a gummed-up injector fan. That blew the chip that controlled that and the flapper motor.

It was just coincidence that the 1st new main board and the 2nd new main board blew when the oven temp was turned on. (Explains why my original main board was still heating the oven just fine.)

I got an explanation that the fuses only trigger with AC and not DC surges. That's why they were intact on the main board and AC power board. The injector fan is DC driven.

[thohry]

I have once experienced that problem, and finally, it was solved by replacing the flapper motor. Hope your case is the same !

[LCbob]

Thanks for coming back with a reply. It is interesting the injector fan was the culprit, as this problem is very well known on HP5890 ( they used to blow boards when the injector fan failed ). I was told many years ago this had been fixed for the 6890s.

[achkata]

If it is well known why agilent did not help? They could guess when you've phoned

[queenann]

Yep, the injector fan blowing out the main board in the 5890 GC is well known. The guys doing the repairs (non-Agilent) mentioned that. They thought Agilent fixed that in the 6890 GC as well.

I'm just a little put-off that both the non-Agilent and Agilent people hadn't pursued the chip lead (U55) in the beginning when it was clear that it was being damaged on every main board that was installed.