Tek TDS 360 Digitizer Problem

[Labrat101]

Hi Just to Say I Just UpGraded  TDS 340 to TDS 360 .
Just for the shear fun
200 MHZ  @ 1Ghz sampling
Works great just have to do a few minor Cap calibration . to fine tune it .
Its an hours work . No firmware changes . No chips replaced .
Just 7 resistors added , 1 cap removed,  2 links removed 0 .

   Have fun do some thing creative 

[james_s]

Hi Just to Say I Just UpGraded  TDS 340 to TDS 360 .
Just for the shear fun
200 MHZ  @ 1Ghz sampling
Works great just have to do a few minor Cap calibration . to fine tune it .
Its an hours work . No firmware changes . No chips replaced .
Just 7 resistors added , 1 cap removed,  2 links removed 0 .

   Have fun do some thing creative

Could you share the details? I have one I'd like to upgrade just for the hell of it. A friend of mine has one that is actually his main scope, I'm sure he'd like the upgrade as well.

[Labrat101]

Hi Just to Say I Just UpGraded  TDS 340 to TDS 360 .
Just for the shear fun
200 MHZ  @ 1Ghz sampling
Works great just have to do a few minor Cap calibration . to fine tune it .
Its an hours work . No firmware changes . No chips replaced .
Just 7 resistors added , 1 cap removed,  2 links removed 0 .

   Have fun do some thing creative

Could you share the details? I have one I'd like to upgrade just for the hell of it. A friend of mine has one that is actually his main scope, I'm sure he'd like the upgrade as well.

I have opened a new subject on this in Repairs.
https://www.eevblog.com/forum/repair/upgraded-tds340-to-tds360-200mhz-1gsas-for-any-one-interested/msg3390308/#msg3390308

Enjoy there are all the details with pics & how to

[cheapskate]

Well, I replaced the acquisition SRAM and it fixed most of the problems I was having at the beginning of this thread. Now the scope accurately shows my input signals over the entire sampling interval. The random stair-stepping issue is also gone, no idea what was causing it. As far as I can tell, the scope is functional.

Unfortunately, it still doesn't pass the diagnostics self test. The new error that appears (inconsistently) is: diagAcq_peakDetectAcq
Peak Detect mode is a special acquisition mode described in the technical reference as

"In Peak Detect mode the sampler holds the minimum and maximum values
over a sample interval. The data points are transferred point by point to be
digitized and stored in the acquisition RAM as they are acquired."

I have never used anything like it before, so I can't really say if it is working properly but it looks like it is. It would be nice to get rid of this error but I'm not sure it's worth the trouble. I do plan on replacing the Dallas RAM and RTC eventually, but loosing the existing calibration during the extraction process would turn this functioning scope into a brick; I don't have the equipment to recalibrate it.



P.S. The CPU errors were caused by a partially disconnected communications option board. It was unable to find the floppy drive which causes a save/recall memory error.

[james_s]

Excellent, it seems I was correct to suspect the acquisition SRAM.

Unfortunately I don't know what that other error could be.

[RPP]

Did you end up using the IS61C64AL-10JLI-TR SRAM?  Any modifications needed?  I have a TDS380 that i'm slowly bringing back to life and I suspect my missing signal on CH1 is due to a similar memory issue.  I replaced a burned resistor on the input of the attenuator board and now have a good signal through the relays, but nothing on the display except an straight line with a negative offset.  This correlates to a -2V reading I get on pins 15 & 16 of the CH1 attenuator.  DC offset on the display shows 0V.

CH2 works fine, though . . .  Something else perhaps?

Any feedback would be appreciated.

[james_s]

If ch2 works fine then I don't think the problem has anything to do with the RAM.

The burned resistor suggests someone severely overloaded the input, follow the signal all the way to the ADC, it's possible the ADC itself has been damaged.

[RPP]

Thanks for the suggestion.  I was able to isloate the problem to a shorted OpAmp in the preamplifer of the attenuator hybrid.  As near as i can tell, the Vee on the OpAmp is backfeeding out of the negative input.  The voltages I measured seem to support this theory.  I've attached a photo showing what I found . . . maybe it will help someone else.