Tek TDS-420a issues - Page 1
Forum section: electronics / testgear

author: ArcticMynx
author_rank: Newbie
timestamp: May 10, 2016, 03:41:11 am
content: I've tried teks forums and everything for help but 0 response-------------------here is the initial post-------------------------------i am having an issue with my Tek TDS-420a scope, as soon as i hit the rear main power the scope turns on and the soft press at the front does not respond to put it into standby.. it powers up immediately as the rear button is pressed.also there is a few errors which come and go they are not constant some days the scope powers with no errors some days it has errorsstory behind itPurchased this scope off ebay as a all LED on no screen scope, after reading several posts i found one that may of caused my underlying issue and it was after testing it was a 27.4Kohm resistor on the processors reset pathwhile more stock of resistors were ordered i had already pulled the power supply out and replaced all the caps on it, just to be safe.. i replaced them with exact spec Caps but Nippon Chemicon's tested the power supply and it read exactly as expected i had to dummy load the 6.4v line as it showed very unstable as soon as a load was applied it was 6.43v so i know the power supply is workingi had also replaced both backup batteries on the unit as one was near dead the other was ok so i had replaced them both. i didnt have any BR 2/3A's i only had a pair of BR-A 3v so i used those, they are same voltage and diameter just longer (old batteries were 2.608v on DSP and 3.103v on CPU board)I've looked but i personally cannot find info on the following errorsa video of the boot up can be found here ( Warning the mic is sensitive so its loud also my camera absolutely HATES to focus when pitch dark i couldn't record it with light as the screen could not of been seen.)http://e-techcomp.ca/files/images/scope/P5050086.MP4more pictures can be taken if anyone asks.the main boards on the underside show the caps to be in ok condition absolutely no leaking no damage no burn nothing... i pulled 2 random smd caps off and tested them they were in spec so i stuck them back on.the Regulator board the power supply plugs into was recapped entirely then a replacement board was installed as i thought i may of had issues with it and it works the same as before nothing changed--------------------------------------Update to datefound out the front ON/STBY switch pads were actually totally knackered, i removed the face and ran my finger across the traces for every button stayed put but as soon as i swiped over the ON/STBY it wiped off in a single swipe so the carbon traces were pretty much done for.. seeing the others were fine and it was just the power button i ran 2 thin wires from the corresponding pins on the connector to where the power button was and used a momentary push button switch ( same one they use in vehicle FOB remotes) and now the front ON/STBY works fine. and it now has a very nice definitive CLICK when pressed..I Still have the issue with the NVRAM CRCC failure on the Libs as pictured abovei notice that its random on the startup test pass and fails.. some times it passes fine sometimes it fails always ++DSP.. im totally lost on this one-----------------------------if anyone reads this part this parts for the Processor board's resistor that failedI read in a post that the resistor under the conformal seal goes open which is for the reset path then realized this isn't the only time i have seen thisi had several Dell 42inch Plasmas that would either totally fail or have alot of snow the same conformal gel is used to insulate the pins on the high voltage Y Drivers.Age and heat cause the gel to deteriorate to the point that it actually turns conductive or fails to the point it cannot insulate anymore... i had the coating on this board tested and it DID conduct, it wasn't a dead short but was told it was enough to get a clean reading.-----------------------------