Electronics > Repair
BK Precision 2120 trace issues
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vexatag:
Note for clarification: The left tan pin is D2, the right tan pin is D1.

Voltage to D1, -116 V. To D2, -121 V. I tried measuring the resistance but got either overload or around 5 megaOhms on both my meters.

EDIT: I also remeasured the voltage between D2 and ground, got a result of around 3 volts. Maybe my testing methodology is borked somehow?
bdunham7:
Yes, there seems to be some issue measuring, so let's back up.  Is the scope partially disassembled so that any of the grounds are disconnected?

So first, let's go back and measure the +260V supply that you fixed earlier, make sure it still has power.  DMM neg lead to ground and pos to +260V.  Then move just the pos lead to the L801-L802 junction, the same 260 volts or so should be there as it is a direct connection.

Next, power down and look at L801, L802, R838 and R839.  You can see how they are connected, L801 and L802 are inductors so they should have a very low DC resistance.  If you measure from the L801-802 junction to either TO D1 or TO D2, you should get approximately 15K ohms--and if not, you need to measure each component separately. 

Also look at all the connections and wiring to make sure everything is firmly connected and you haven't missed anything.
vexatag:
Scope is fully assembled, just out of the case.

TP260V and the L801-L802 junction both have 265V. As for the megaohm resistance I was measuring on the wrong side of the inductor :palm: Both are around 15K to D1 and D2.

Ground to D1, 37.4 V. Ground to D2, -3.3 V.
bdunham7:
Alright, just to be clear, you measure from the L801-802 junction to D1 and D2 and each time you get 15K?  I don't see why using the wrong side of the inductor would matter.  Can you just check L801 and L802 to see what their DC resistance is?

I'm trying to figure out how D2 can be at -3.3 volts.  Can you also measure again voltage from D1 to D2?
vexatag:

--- Quote from: bdunham7 on July 26, 2020, 11:40:35 pm ---Alright, just to be clear, you measure from the L801-802 junction to D1 and D2 and each time you get 15K?

--- End quote ---

Measuring from what I believe the junction is, I get 15k ohms. Measuring from the other side, I get 5.3 mega ohms.

L801 measures 7.3 ohms, L802 measures 7.1 ohms. Each leg has continuity with every other leg as well, don't know if that's important to mention or not.

Checking D1 to D2 gives 73 V.
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