TSP

In this episode Shahriar investigates a peculiar problem with a SRS DS345 function generator. The instrument does not appear to produce the correct output signal frequency. After some investigation it becomes clear that a few of the display digits are not active which hide the actual frequency settings. The problem is traced to a broken resistor on the display driver. The schematic of the instrument shows that the resistor is responsible for strobing the affected seven-segment digit. After the repair, the instrument’s performance is verified including the OCXO accuracy.
The Signal Path
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[@imogenx5668]

I know almost nothing about electronics, I took an electronics class in high school and I own a $5 multimeter... thats the limit of my understanding... but I still love watching this, because it's an interesting puzzle! Thanks for the great videos.

[@k1mgy]

At 4:40 you connect the function generator directly to your (rather expensive) scope. Would it be safe to check the generator outputs with a dmm before doing so? Not sure what your scope can tolerate, so this may be a stupid question. Here's an idea that can save cash and foster participation. The Signal Path "send me your broken test equipment" program. Lucky submitter pays freight both ways, and cost of parts. Their gear is featured in a repair video. They learn how to go about the repair process and, should you be successful, get it back in hopefully-functional order. I learn so much, watching you go about these repairs and bet others do, too.

[@stargazer7644]

No worries, not stupid at all. That scope's inputs are good to 300V RMS. That's fairly typical for a scope. Scope inputs are high impedance, so they're fairly bulletproof. Be very careful with anything with a 50 ohm input though. The voltage limits are often right on the front of the device.

[@littleboot_]

I love watching your videos, it teaches a lot about troubleshooting circuits. (The stuff you don't learn about in school)

[@ChipGuy]

Nice find and nice repair. When I did HiFi Repairs in the early 90s I have seen broken resistors like that quite a few times. Those broke within about 2 years after manufacturing. Investigations by the engineers back then concluded that their bodies were overstressed in production by the pin bending+cutting machine, because some of them (their bodies) were a bit longer than they should have been.

[@lmamakos]

It looks like the leads on that resistor were "stretched" a bit tightly. I wonder if a few years of thermal cycling may have finally caused the mechanical failure.

[@maurosobreira8695]

Always learning with your videos, Shahriar. Thanks for posting!

[@JGunlimited]

I grabbed a copy of the manual to follow along... it's amazing how you can make sense of those schematics!

[@TheRadioShop]

Thanks for a nice repair. Enjoyed watching you work through this one.

[@stargazer7644]

I would never turn on a device someone else has been in without looking inside first. And yes, I was screaming at the screen at 5:50 . Thanks for the laugh.

[@rpbale]

Your approach to diagnosis is very helpful. We never seem to be working on the same instrument but none the less it's super helpful. I've got a broken Fluke 5300A on the bench that I wouldn't have the confidence to tackle without watching your videos. I'm currently stuck but my confidence is high! Thanks

[@kieranj67]

Nice repair, thank you

[@commonmogoreanu7135]

Thank you. The wine and the repairs are very appropriate. Ignore the haters.

[@BR.]

You explained very well. Thank you!

[@douglasRbrown]

thank you for the great videos

[@bundylovess]

Nice repair big thumbs up

[@andypalm7061]

wow,how lucky to be only a small issue. Very interesting problem.

[@CT1JRZ]

Nice channel you have here! Best regards

[@GeorgeTsiros]

Come for electronic equipment repairs, stay for oscilloscopes dancing not to sting ^_^

[@bfx8185]

Finally something liiiiittle bit difficult :) Thx for nice video ;)

[@johnny-s40]

Nice !!👍

[@aaaaa-yv1zr]

I would love to see DG535 teardown!

[@EngineeringVignettes]

From my time as a repair tech [in a past life :)- ] I would say that the base resistor was intentionally broken (sabotaged). I have seen this done before in the repair industry, its a nasty practice to get into and I never did it myself. The guy who tried to fix it before you likely broke it on purpose. A 150 ohm resistor providing base current will never shatter that way by itself and it did not look like there was any mechanical interference or pressure on it (the PNP transistors were higher than the resistor, they would have been disturbed if so). It just goes to show that its best to be the first guy to try and fix something that's broken; all you're fixing then is the initial problem. - Eddy

[@AureliusR]

Why would they break it on purpose? Also, resistors CAN break that way due to manufacturing faults or thermal stress. If they were to break it on purpose, it would be to get more business, theoretically, right? Well, that seems to have backfired. You can't return a broken unit to the customer.

[@ydonl]

A function generator sync output is typically a square wave; the purpose is to use those very fast edges for triggering other devices, e.g. the sweep of an oscilloscope. If you read the manual description of "Sync pr Er" carefully, you see it says the output is not "+/- full scale", which is what you would expect from the typical comparator circuit for generating sync -- just on or off, making the square wave. The sync output of this instrument was not square, as shown on the oscilloscope channel 2 trace, but some other oddball shape. I believe the sync circuitry was bad in some way, and went undetected in the course of this repair. Tinkering with the level might have allowed the detection circuit to declare the output okay through whatever the test is that it uses, but not really because it was a correct signal. I think there is still potential in this instrument for some fun troubleshooting and repair! :)

[@walterlee3871]

Thanks very much for such a high quality video! I am wondering where I can download the schematics. I have tried downloaded several versions of the DS345's manual and it turns out that the shematic part of this manual had been cut off.

[@anonymousarmadillo6589]

Xdevs

[@ChrisJackson-js8rd]

more lock in amplifiers please and thank you :)

[@waverleyrocker]

TSP, a great video as always. Do you show us all the repairs you attempt? Or do some fail?

[@PlasmaHH]

Regarding the cabling of the 10MHz: I have seen this rather often, it isn't that bad, the path is rather low impedance and doesn't get disturbed by things easily and the signal is quite strong so you have some 10MHz waveform (often only remotely square or sine) that is only disturbed a little but for the PLL its piece of cake to get locked to it.

[@vanessaphung4367]

Do you have any video on repairing SRS DG535 power button or unit power supply?

[@feijojr]

Hello! Great video! Thanks. One question, do you know where can I get the schematics? The manual I have don´t have any diagram. Thank you for any help.

[@TheCondoInRedondo]

I can find all manner of user/datasheet/programming documentation for this device. But I cannot locate a copy of the schematics/service manual. Where did you obtain your copy?

[@kirkpennock2997]

What will you do with repaired stuff?

[@pa4tim]

Funny, you often have repairs that turn out to be to easy and you "complain" about that being to easy, and now you have an interesting more unusable fault that requires some clever thinking to find and then you delete the footage ;-) Murphy needed a slap in the face to stop laughing. As usual, still a nice and educational video

[@Thesignalpath]

Haha... Yes, you are right. I was pretty frustrated when I lost that 5 minute footage. Repairs by definition are unpredictable, hopefully more complex repairs will come up soon.

[@simontay4851]

How did you manage to loose it. Loosing footage is the sort of thing inexperienced noobs do. Is there a bug in the camera firmware/software?

[@simontay4851]

Or is your SD card going bad?

[@pa4tim]

Or it turns out he's human after all :-)

[@Thesignalpath]

I took a shot, didn't like it, went back to erase the shot and I accidentally erased two clips one of which was 5 minutes long. The touch interface on the Sony camera is not the greatest thing in the world.

[@gacherumburu9958]

👍👍

[@Fusionx916]

What is the brand and model number of that isolation transformer? Ive been looking for something like that for SMPS design

[@Thesignalpath]

I have a video on it on my channel. It is a Sencore PR570.

[@Fusionx916]

Thanks just watched your video on this unit. Man what a lucky repair job you got. A fully working unit is very expensive!

[@Fusionx916]

Do you mind doing a review/teardown of the Sencore PR57? It looks like shit but it's nearly 10x cheaper and looks like it does nearly the same thing as the PR570. Just let me know how much I need to donate on Patreon to make this happen.

[@FennecTECH]

The way you can give back to your supporters is to use the money to make more high quality videos Pour your woul into the content and we will suck it up I buy youtube red spesificly to support the creators of content Without red i would be adblocking. Just keep up the good work and everyone will love your content :D One thing to remember Dont overwork yourself If you do your quality will suffer and then nobody will be happy

[@FennecTECH]

some content is great for daily uploads this is not Dont turn this into a daily series It might be better for the ad revinue but it wont be better for your viewers and youll burn \yourself out. Just putter along atr your own pace ne of the most importan things for a channel is a schedule Keep a backup video or two for when shit happens PS dont fall for the temptation to use clickbait While it works everyone hates it

[@dangrie158]

When it first said "sting" and "st pass " I just thought it would stand for "SelfTest(ing)" and "SelfTest passed"

[@stargazer7644]

As soon as he hit the first frequency button and the display blanked after showing all zeroes, I realized the first digits were missing.

[@PapasDino]

Shariar - what did you do to "modify" the potentiometer that solved the Sync error?

[@AureliusR]

It sounds like all he did was move it back and forth a couple times to clean any oxidisation that had formed on the surface of the potentiometer.

[@volcanowb]

Love ya man but you've succumb to the Chinese equipment.

[@Thesignalpath]

What Chinese equipment?