Capacitators. It's ALWAYS capacitators.

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03-30-2013, 08:45 AM
N8YX

Capacitators. It's ALWAYS capacitators.

Had a Tek 7603 go funky on me a couple weeks ago. For those unfamiliar with the series, they had an on-screen character generator option which annunciates range and mode selections for the numerous plugins which work with the instrument.

Except these characters - along with the horizontal trace itself - caught a case of the jitters on powerup. The instrument was working fine previously.

Playing swaptronics with a good display generator board showed the problem was still there. Off to check the power supply voltages. All looked good except for the -15V line; it was showing -12.7V.

Hmmmm.

Scoping things out (with a working scope) showed a nice half sine wave on the -15V rail. Identifying the bad filter capacitor was easy. Getting the friggin' PSU out of the scope then getting the friggin' cap out of the PSU itself was another matter entirely.

Once a replacement was fitted and the PSU assembled, scope fixed. This is the third time (on two instruments) that capacitors have played a role in their malfunctioning. 'crk's scope issues seem to revolve around bad tantalums as well.

Food for thought for those of us with "vintage" test gear.
03-30-2013, 09:37 AM
K7SGJ

Over the years, it has been my observation that most OEMs use components, especially caps, and tants in particular, that are rated very close to actual operating voltage. That is the very reason I have a huge inventory of them in most every value made. Should there ever be a surge, pulse, or condition that exceeds the caps value, even briefly, it will kill the cap. Tants are not as forgiving as electrolytics. As a result, any replacements I put in are with the next higher voltage rating (space permitting). While it is a cost factor in production, it is of little consequence during rework, plus a little head room is always good. Just ask Max.
03-30-2013, 10:27 AM
AE1PT

Quote:

Originally Posted by K7SGJ

Over the years, it has been my observation that most OEMs use components, especially caps, and tants in particular, that are rated very close to actual operating voltage. That is the very reason I have a huge inventory of them in most every value made. Should there ever be a surge, pulse, or condition that exceeds the caps value, even briefly, it will kill the cap. Tants are not as forgiving as electrolytics. As a result, any replacements I put in are with the next higher voltage rating (space permitting). While it is a cost factor in production, it is of little consequence during rework, plus a little head room is always good. Just ask Max.

You bet. Strangely enough, the 'next value up' or so in working voltage may be all that's available anymore. If something comes across my bench for repair--but shows function the likely culprits in order of failure seem to be capacitors, resistors, discrete semiconductors, tubes, miniature variable caps, diodes, and IC's. The hobby/basic service grade stuff I buy anymore (Eico & Heathkit novelties) starts rehab mode as soon as it comes out to the shipping box. Have not had any issues outside of cleanup with the lab grade stuff--fingers crossed for the future...

Poor Max. Too much Coke... :cool2: