54520A repair

Apr 16, 2007 4 Replies

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jvadillo 19 years ago

Hello all,

I recently purchased a broken 54520A hoping to be able to repair it. The seller said that the screen was faulty. However, after the oscilloscope arrived, I saw very soon that the problem was not the screen but something else.

When the oscilloscope boots, the fan turns on and all the indicators on the front pannel light-on. But it hangs there. No keyboard response and nothing displayed on the screen. However, the screen is working, as when I turn off the device, sometimes I can see the beam on the display and some noise.

The indicators keep lighted on until you turn the oscilloscope off again.

Could anybody help me? Its a great oscilloscope, but it just does not work :-(

Juan

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James Sweet 19 years ago

I assume this is a DSO? Start with the simple stuff, check the power supply voltages, see if the CPU clock is running, have a look at the reset line, that should provide some insight.

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jvadillo 19 years ago

Yes, its an HP 54520A digitizing oscilloscope.

I will check if all the voltages are OK. According to the service manual I have to search around for a 2 Ohms 25 Watt resistor to load the power supply.

I will post my results here.

Juan

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Jorgen Lund-Nielsen 19 years ago

Here are aso some experts to find:

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Jorgen dj0ud

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jrwalliker 19 years ago

Juan,

There may be a lithium cell which is used to maintain the static ram where calibration data is stored. In the 5454x series of 'scopes the system locks up exactly as you describe when the lithium cell is discharged. This seems to happen about 15 years after manufacture.

The service manual makes no mention of this problem!

I had a similar problem with my HP 54542A 'scope and another poster had this problem with his HP 54540.

Replacing the lithium cell and running the self-calibration fixed the problem for both of us.

For more information, search this group (sci.electronics.repair) for "54540A".

John

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