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Products => Test Equipment => Topic started by: Jay_Diddy_B on May 30, 2015, 02:23:43 am

Title: Tektronix 494AP Spectrum Analyzer Repair
Post by: Jay_Diddy_B on May 30, 2015, 02:23:43 am

Hi Group,

Time to share a repair that I made to a Tektronix 494AP Spectrum Analyzer.

A friend gave me the SA to repair, it would not work at all, it would blow the main line fuse at the back of the unit.

Schematic

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154384;image)

I did some poking around with a meter and I found that one the rectifiers in the bridge was short-circuit (CR3096 or CR4094). In addition one the main electrolytic capacitors was short-circuit (C6101 or C6111).

The rectifier was easy to repair, I used a 1N5408 3A diode.

Electrolytic Replacement

The original capacitor in the spectrum analyzer were manufactured by Aerovox. They have a 5 pin base. This was probably chosen by Tektronix for mechanical stability.

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154386;image)


I decided that I would make some adapter boards, so that I could use two pin snap-in electrolytic capacitors as a replacement.

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154388;image)

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154390;image)


I went to all this trouble with the adapter boards, because the end of the capacitor pokes through a hole in the chassis. The replacement capacitor has to be in the same place as the original.

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154392;image)

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154394;image)

Working again


The Spectrum Analyzer works fine now that the capacitors and the rectifier have been replaced.

(https://www.eevblog.com/forum/testgear/tektronix-494ap-spectrum-analyzer-repair/?action=dlattach;attach=154396;image)

I found the Service manuals at:

http://www.ko4bb.com/manuals/ (http://www.ko4bb.com/manuals/)

Regards,

Jay_Diddy_B

Title: Re: Tektronix 494AP Spectrum Analyzer Repair
Post by: w2aew on May 30, 2015, 03:53:05 am

Sweet!

Title: Re: Tektronix 494AP Spectrum Analyzer Repair
Post by: Muxr on May 30, 2015, 04:10:48 am

Very cool.

Title: Re: Tektronix 494AP Spectrum Analyzer Repair
Post by: photon on May 30, 2015, 09:42:44 pm

Thanks for posting. I always find such repairs very instructive.

Title: Re: Tektronix 494AP Spectrum Analyzer Repair
Post by: Vgkid on May 30, 2015, 10:31:16 pm

Very cool, those are the same style of caps used in the 3456A's infamous power supply. I just used a radial cap, and bent the pins for best fit.