HP 9810 A transformer

[teenix]

(08-04-2016 12:04 PM)calc_you_later Wrote:  I have recently acquired an HP 9810A and want to get it working again. When turning it on it blows the 6A fuse and no lights on the console turn on, so I took it apart and I think it's the transformer that's the issue.



In the image there are 7 contacts, from top left to bottom right they are:

7 6 5
4 3 2 1

When I continuity test 7, 6, and 5 they are all connected, could it be a short in the coil somewhere?

Also any ideas of what else I could try / test?

Thanks

A few thoughts...

I don't know if service manuals are available online, but if so, it would be a good first step as it would surely offer some testing procedures and possibly circuit diagrams, otherwise testing for unknown values may not prove valuable. There are many wires coming from the transformer, not just the ones that are numbered. The extras (black and green) look to be in a white sheath.

Depending on what you used for a continuity test, the result may not prove much as the transformer windings will (should) have little resistance to DC current and may just appear to be shorted.

Does the unit have multiple mains input voltage settings, say for different countries. It may be switched to a wrong setting.

Look for components that look damaged, corroded, swollen, or blackened and try to detect any smells of previous burning around the circuit boards and power supply area. (Mains power disconnected of course) Look for "gunk" that may have leaked out of components or has gotten into the insides accidently (coffee etc) and is causing a short.

If there are plugs from the transformer to the power supply board, you could try unplugging them and power up again. If the fuse stays in tact, the problem is from the power supply into the circuitry.

If the 9810 construction is modular then you can unplug as many modules as you can and try to power up again. You might be able to narrow down which module is causing the problem. You have to be careful here as some circuitry may be powered up in an unstable state with things disconnected and may give you more grief.

If it powers up ok with modules disconnected, you could measure the AC output from the transformer, but you would need to trace the leads to the power supply circuit and work out what lead does what. Measuring the DC power supply voltages would be a next step. Again a service manual would be invaluable.

If you do go unplugging things, try to mark everything you can, or take lots of photos.

Lastly, while fiddling around beware of high transformer voltages, remember they can be lethal, especially if one hand is resting on the chassis and the other touches the mains wiring.

cheers

Tony