Recent Posts

1

Microcontrollers / Re: It Came from Mainland China: Bootleg MCS-251 "32-Bit 8051"

« Last post by PCB.Wiz on Today at 03:21:13 am »

However, it seems that they're a clone of Intel's MCS-251 microcontrollers from the 1990's, but with lower cycle counts for instructions, and better peripherals.

Yes, the STC8H parts have moved the '1T' 8051 space.
Previously, most 8051 1T parts were 1 cycle per byte, makes sense as they historically fetch a byte at a time.   

The latest STC parts improved that with wider fetch, to have even 2 & 3-byte opcodes execute in 1T, it is only branch opcodes that need more than 1T, if taken.
 

2

Metrology / Re: Why don't we see more TDC based high-resolution ADCs?

« Last post by bdunham7 on Today at 03:08:37 am »

Multislope can be much faster, for one thing.

3

Metrology / Re: I bought the very Last Symmetricom SA.22C in the shop!

« Last post by Johnny B Good on Today at 03:03:42 am »

After I opened it and take out the PCB, it became obvious that the problem is a thin film filter that is normally glued to the rubidium lamp assembly fall from its place. I glued it back with high temperature epoxy and now it locks fine.

 I wasn't sure what this "thin film filter" was that you were referring to so I took a look at my photos to figure out what a "thin film filter" would look like.

 My best guess was that it was the mm or so thick circular disk of (quartz?) glass I've circled in the attached image acting as a closed window to retain the heat within the lamp enclosure. AFAICR, the lamp is maintained at a temperature of 75 deg C so the high temperature epoxy glue you've used should be ok if it's rated for 100 deg C or higher.

 I've not had any reason to think that it had any other purpose than to minimise heat loss from the lamp so I guess the reason why it couldn't achieve atomic lock in this case was simply due to the lamp failing to reach its full operational temperature.

 Thanks for that feedback which adds yet another easy to fix stock fault to the growing list of failure modes to consider by anyone else attempting to repair a faulty SA.22C.

4

Repair / Re: Tektronix SC502 Alt and Chop mode fault

« Last post by BlownUpCapacitor on Today at 02:53:04 am »

I did some troubleshooting and found that the trigger signal wasn't being amplified well. Q350 looked like it could be causing some problems. So I desoldered it and lo and behold, it has a big ass crack in it!

Will a 2N3904 transistor be a good enough replacement? the original is 2N3565

Also the new 7472 IC arrived and it's back to the random switching

5

General Technical Chat / Re: H5N1 bird flu and how we're risking another global pandemic

« Last post by Halcyon on Today at 02:45:05 am »

We were told to get vaccinated to protect others which was a lie. Our government even mandated it for care home workers and they were going to also mandate it for all frontline NHS staff. Fortunately they realised it didn't prevent transmission and cancelled mandates. The authorities have pushed far more misinformation, than crackpots on the internet.

I prefer to stick to the hard evidence. I'll believe it when I see proper, randomised data to show it works.

What a load of crap. Whilst the vaccines might not have prevented all transmission, it certainly had a significant impact on transmission rates and for those that still ended up catching COVID, it significantly reduced the symptoms in most vaccinated people. There's plenty of evidence that supports this. The fact is, the vaccination programs saved a lot of lives and made the lives of millions of others far less miserable.

I continue to get vaccinated against COVID every 6-12 months based on Australian government and doctors advice, and I'm yet to catch it. I spend quite a lot time on public transport and around people as well.

6

Other Equipment & Products / Re: PCB Ultrasonic Cleaner Recommendation?

« Last post by EEVblog on Today at 02:42:43 am »

Old thread, but no point making a new one.
Finally got myself a small ultasonic cleaner.
Fire some recommendations at me for PCB cleaning solution...

I trust Chemtools here in Sydney, but anything else worth considering?
https://www.chemtools.com.au/product/electrical-electronics/cleaners-flux-removers/pcb-flux-remover/
Thanks.

7

Metrology / Why don't we see more TDC based high-resolution ADCs?

« Last post by nimish on Today at 02:37:06 am »

Stupid question but since it's easy to get an extremely stable clock source -- 0.05 ppm is like $50 retail -- and measuring long time intervals precisely is relatively easy (seconds to sub-nanosecond precision) why use a complicated multi slope ADC when bolting the voltage to time converter to a TDC gets you most of the way there? What am I missing here? Comparator noise?

8

Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Today at 02:34:31 am »

Earlier I took measurements to see if I could find any shorted pins.

I made a few errors due to not realizing pins 21-24 weren't in sequential order with the SEG lines, so I measured DP2 to SEG-E (by way of measuring the VFD pins directly) thinking the pins on the IC were next to each other.. By the time I realized this error, it was late and had to call it a day.

From the measurements I took, none of the pins were shorted, however, one odd thing I noticed was SEG-COM wasn't connected to ground (unless I'm wrong, I've been using chassis ground as it appears ground is connected to chassis ground).

Maybe SEG-COM is floating, but thought to mention it.

After measuring for shorts, I powered the unit and took scope measurements (see attached - file names are according to which pin was measured). Upon powering it, I checked the heatsink (again) and it was fairly cool. After keeping the unit powered for about fifteen-minutes (the longest I've kept it powered since the display stopped working) while taking scope measurements, I turned off the unit and touched the heatsink. This time it burned the back of my index finger; believe this indicates something is wrong.

The 5v measures about 4.8v I believe, however, whichever the voltage is falls within the range in the service manual.

9

General Technical Chat / Know of any good books/sources of useful electronic schematics?

« Last post by ballsystemlord on Today at 02:20:01 am »

Hello,
When looking up how people make this or that, I can't help but find that many of the schematics offered online are either not functional or poorly designed. It's not just me either. Some YT-ers make videos about fixing bad circuit designs you can find online.

Towards the end of getting a set of good/workable circuit schematics, I searched for books on the subject. I found some, but they're all from the late 1960s though the 1970s. This means that a lot of things can/have been converted into ICs or improved through the use of alternate tech, such as IGBTs/MOSFETs. So such books are a bit dated.

Do you know of good books or resources for circuit schematics?

Thanks!

10

Buy/Sell/Wanted / Element 14 Australia Fire Sale

« Last post by EEVblog on Today at 02:19:47 am »

Up to 99% off AU warehouse sale, the spreadsheet is vast:
https://au.element14.com/fire-sale?ICID=I-HP-LB-FIRE-SALE-MAR24-WF3616377