MP 780 will not power up

[Trigger 37]

jflan,

The block diagram for the MP730 shows the two pin connector is the AC power coming in. The 7 pin connector is the low voltage DC power going to the main logic card. It also shows that there is one cable coming from the operator panel and that is a 17 wire cable. Therefore, the main power switch that comes from the operator panel goes to the main logic board, and that is what turns the power on and off. Your power supply may be just fine, and it could be the switch, or one of the components on the main logic board. That could be a lot more expensive.

 

[jflan]

On this PCB there is what appears to be a 2-pin low voltage header immediately to the right of the 7-pin.
I have a nice image, I just can't see how to attach a file here

Maybe in this manual there is a pin-out diagram that details these two headers.
I'll keep looking around.

 

[Trigger 37]

jflan,

I don't know what you mean when you say,

I have a nice image, I just can't see how to attach a file here

You don't want to mess with the 2 pin connector. Just take your volt meter and attach the black lead (ground side) to one of the good ground connections on any of the sheet metal in the printer. Then take the red or voltage lead and measure each of the connector pins at the PC board. The voltages should be +5, +19, and +27 volts. If you get these readings the power supply is OK. It is some other problem.

 

[ghwellsjr]

The Upload link at the top of this page is supposed to provide an easy way to post images but one other person said it wouldn't work. If it doesn't work for you, send an email to the Administrator.

 

[jflan]

Thanks all.
It's the lower image.
The connection to the left of the 7-pin is for an early model external regulator.
I have the integrated regulator and don't have this connection.

 

[jflan]

The voltage check from left-to-right @ the 7-pin connector is :

[0.0] [0.0] [24.2] [26.8] [4.9] [0.0] [0.0]

 

[ghwellsjr]

Try what websnail discovered:

http://www.nifty-stuff.com/forum/viewtopic.php?id=2081

Let us know if it works for you.

 

[jflan]

Thanks, ghwellsjr.
I will try that before ordering a new power supply.
Too bad so much disassembly is required to access those connectors on MP780

 

[Trigger 37]

jflan,... I see you finally got the voltages measured. Since the MP780 Service Manual does not list the power supply voltages, I was guessing at the voltages but the ones you measured seem just fine. Of course there could be one missing. Logic level is +5 volts, and printhead driver and motor controls are about 24 volts. So what you measured seems OK. These symptoms are not pointing to an error on the mail logic board. Try out the suggestion above you may be supprised.

 

[jflan]

Thanks Trigger37.
BTW, what's your take on the "missing" readings on four of the terminals ?

I sure wish that dang service manual listed the ouputs !