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TDS520 Repair/Errors

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TDS520 Repair/Errors

Post by ironmanisanemic » July 12th, 2018, 8:16 pm


I have recently acquired a TDS520 non letter scope, and have just finished replacing all of the caps. I am still getting power on errors on processor, acquisition, and attn/acq interface. After warmup though acquisition passes upon power up.

When i go into the error log after power up and attempting a SPC calibration I see the following errors:

Code: Select all

ERROR: 242 wrong hardware configuration Dsy Vect0 mem size probe, expect: fff, actual: 0

ERROR: Cal meas clipped at min dig output Ch1 Gain Cal of Attenuator

ERROR: Cal meas clipped at min dig output Ch2 Gain Cal of Attenuator

ERROR: Characterized values out of bounds Vertical

ERROR: 2260 Calibration failed Repet Cal Failed

Also, im not sure if its a problem, but on a cold startup the offset of the traces are way off the screen. After few minutes then they all come down to where they should be except for the 5mv and 1mv. Those 2 show a bunch of noise and have a significant offset.

I havent seen much in the way of collateral damage from the old leaky caps, there was one resistor on the processor board that the vias were damaged that i repaired. Beyond that i have found nothing. Does anyone have any suggestions or areas that i should start looking at?

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Re: TDS520 Repair/Errors

Post by ostapip1 » July 13th, 2018, 12:16 pm

ERROR: Characterized values out of bounds Vertical


Check power supply of these marked -X- -X- chip / and power supply on all microchip
And RP911 and near area check too
Circuit diagramm
https://drive.google.com/open?id=0Bz230 ... G03NXowQXM
https://drive.google.com/open?id=0Bz230 ... EJ0eVhSdWM

Good luck )))

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Re: TDS520 Repair/Errors

Post by strick » July 13th, 2018, 12:27 pm

The Dsy Vect0 looks like a display memory error or error with the associated circuitry on the CPU (top) board - if it is allowing the scope to function otherwise, I think chasing it down might be real tough. I've never had much luck here. The reason is that the trouble shooting guide (TDS520 Component Level Diagnostic and Repair manual) wants you to run special diagnostics. I suspect TEK had a bunch of special routines that ran from a computer hooked to the debug port, but I have yet to see any of them. If anyone else has, please advise!!!

The first thing with the ACQ board that has had ANY damage from the SMC electrolyte is to wash the board with either simple green (scrub it real well, wash it off and dry it) or 90%+ alcohol. If any of the electrolyte is under a chip or transistor, strange things will likely happen. Use extensive static precautions to avoid smoking the CMOS Static ram.

The traces being well off of the center in these scopes (not the 540B and later) generally points to the Analog DAC control system. using the 520 manual (from K04BB), you need to examine the inputs and output of U901 and U931-U934. These set the offset and DC balance for the two channels. Channels 3 and 4 do not use the precision voltage preamps that 1 and 2 do. Generally speaking, the 540 and 540A series attenuators are generally not the problem with offsets like they are with the 744A and 540B and later series - totally different methods of attaching to the acq board.

The other place the offsets could come from is a problem with the op amps (buffers) that the DAC control uses to feed the preamps. These are U1201, U1202, U1101. I would also look at U1102, U1103, U1203 and U1204.

I once had a scope that I repaired that had a channel that did similar things and the fault was a corroded (but not visible) input from the J1200 shld (probe ground). I had to run a wire from the shield to pin 10 of U1202 to finally clear it... I simply monitored the voltage input to pin 21 (-VIN) of U1200 and saw that it was slowing changing as the scope warmed. Then I watched the four inputs below until I figured out that the shld part was changing as the chip warmed.

Realize that DC Balance, Offset and Fine Offset AND the shld feedback loop all feed into -VIN on the Preamp, so that any that vary when they are not supposed to will cause problems.


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