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8 ай бұрын

In this episode Shahriar repairs an SRS SR650 dual programmable filter. The unit powers on with nearly all the front-panel LEDs illuminated but does not respond to any buttons. Schematic and internal measurements show a lack of activity on any of the main processor pins which is traced to a faulty inverter IC responsible for clock generation. The main SRAM IC is also missing and needs to be replaced.
Additional analysis of the circuits and modifications are also presented. However, the unit develops a new problem due to very high thermal dissipation of the 5V regular and full bridge rectifier. A new rectifier is installed and the faulty 5V regular is also replaced. The QuantAsylum QA403 Audio Analyzer is used to characterized the filter and ensure both the high-pass and low-pass filter sections are functional.
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Пікірлер: 52

@IanScottJohnston

Back in the day we used to have problems with the same type of oscillator circuit, i.e. some brands/type of 04 inverter would be temperamental in starting up, some even double oscillating!.

@OctavMandru

Repairs are everyone's favorite!

@loueckert4970

Thanks for the training. I spent my carreer working on HP test and measurement gear, mostly RF and microwave. From 1970 to 2015. Happily retired, but miss the challenges of component level repair. Ex-USN ET.

@ryebis

Great analysis and repair, love how you approach the problem solving. Cheers.

@Alamagosa

Regarding the RC marked capacitors, the schematic shows a LT1037 decompensated operational amplifier which is only stable at gains of 5 or greater, so adding a feedback capacitor between the output and inverting input is going to cause a lot of peaking if not outright oscillation. 130 picofarads is pretty low, but is way larger than would be necessary to compensate for stray capacitance at the inverting input. I thought maybe the board used LT1007s instead which are unity gain stable, but your video shows LT1037s on the board.

@bbrand6755

In EEVblog

@kamikazekk-df4vz

Perfect diagnosis and repair of course.

@mansnilsson4382

It is no surprise you are getting noise with 40dB gain in the filter. A much fairer test would be to run 0dBm in and look at S/N in that setting. Other than that, crazy good response curves. Truly a problem solver filter!

@DasIllu

This thing might be the wet dream of any CW operator with mild hearing impairments.

@supercompooper

Christmas has come early❤

@glasslinger

An amazing instrument with that rate of cutoff! Kronhite makes a lower cost version that is entirely analog using ganged pots for the filter adjustment. Of course nowhere near that cutoff rate or dynamic range. (or price!) What era is this instrument? Looks sort of 1980's? I had the impression the 7805's were kill proof with the thermal shutdown.

@der.Schtefan

You know, this video, with the failing inverter, vintage chips, clock generator, and mystery capacitors floating in the air, reminds me a lot of Adria's Digital Basement, and his "whodunnit" style Amiga/vintage PC repairs ;)

@leandrocartes534

the signal phat hello may from Argentina broooooo 🇦🇷

@xThirdOpsx

Hello Shahriar!

@kevy1yt

Also: how are the DACs designed to affect Fc in the filter loops to get smooth Fc changes instead of the discrete Fc poles/zeros caused by the resistors and capacitors switched in or out of the filter loops?

@paulpaulzadeh6172

Nice , dry capacitor may cause diode bridge failed, high ripple current,

@jabelsjabels

as someone more familiar with synthesizers (the musical kind) than high-end test gear, that thumbnail is crazy lol

@Meow-hw5wi

I have another instrument, that an 74hc04 is dead in the PFD path of a PLL, replaced & everything worked. Wondering why those 74XX04 failed so frequent :(

@thorstenstraub3657

Hello, rolloff steepness and passband flatness are great, but I am suprised to see that the 60 Hz powerline has such a big influence. Is this normal for this device (or similar devices from other vendors) or is it a malfunction of this particular unit?

@kevy1yt