Electronics > Repair

Analog oscilloscope repair

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Jim95:

--- Quote from: KJDS on June 20, 2014, 08:04:50 pm ---If you want a summer project fixing Hitachi scopes, I've got a dozen in the repair pile.

--- End quote ---

This is tempting...

Jim95:
Today I've tested the chip and its good as dead as suspected. What is odd though even with that chip removed I've still got a voltage drop of around 0.6/0.5V. Any ideas what this could be from, I'm going to test all the diodes later.

tautech:

--- Quote from: Jim95 on June 21, 2014, 12:21:15 pm ---Today I've tested the chip and its good as dead as suspected. What is odd though even with that chip removed I've still got a voltage drop of around 0.6/0.5V. Any ideas what this could be from, I'm going to test all the diodes later.

--- End quote ---

My first suspect is normally caps, particularly Tantalums.
If it is a LV PCB, a finger can find the hot ones.

What_NZ:
Without knowing the circuit that provides that +5v rail. I wouldn't rule out that voltage drop being caused by the power supply off circuit. If you could post the other circuits or check all the way back to the source again, it would be worthwhile.

Also suggest to check the filter caps at the power supply as if it just a basic supply the extra loading could be just dragging it down. Would be interesting to know how much the ripple is increasing when the +5V rail is loaded.

elliott:

--- Quote from: KJDS on June 20, 2014, 08:04:50 pm ---If you want a summer project fixing Hitachi scopes, I've got a dozen in the repair pile.

--- End quote ---

Someone is in for a treat of there is a V-1150 or similar in that pile. I've got one up and running, but it was a frustrating process.

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