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Can you better identify "J4" or give the capacitor designator from the service manual?
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One of the common failure points is a tantalum 47 uF cap (C1318) that filters the DC supply to the HV generator. There is a choke that may smoke until the fuse gives. Measure the resistance from ground to the fuse. If it is near zero ohms, pull one end of that cap to see if the short clears. If it does, replace the cap. Be sure to only use the correct fuse. Then you can go and check all the low voltage power supply test points. If you have another scope, check the ripple per the service manual. The 475 is a fine scope. Regards ----- Original Message -----
From: "JR" <jswrussell@...> To: <[email protected]> Sent: Sunday, August 12, 2018 3:17 PM Subject: [TekScopes] Resurrecting a 475 - Request for Guidance I have recently become the proud owner of a 475 that I found abandoned at the side of a road! Other than a couple dents in the casing, it appears to be in pretty good condition. After replacing the fuses, I was greeted with what appeared to be a very fuzzy trace when turning the power on. However, very soon afterwards, a resistor directly adjacent to the J4 connector on board A9 (listed in the manual as 'interface circuit board assembly') began to smoke, at which point I powered it off. One of the leads of the resistor in question is connected to the positive side of a orange dipped (tantalum?) capacitor, which leads me to suspect that it may be the culprit, given all that I have read so far regarding worn out and failed capacitors on 400 series scopes. When testing the capacitor in the board, it certainly seems like it's shorted, which I presume would explain the smoke from the adjacent resistor. I'm hesitant to power it on again to check all the rail voltages in case I further damage the resistor. I suppose I should start by verifying which capacitors are good and bad, and replacing the failed ones? In this case, is there a definitive criteria for determining which capacitors are good and which need to be replaced? Or should my attention be directed elsewhere first? Any advice and suggestions would be greatly appreciated. |
