Recent Posts

1

Projects, Designs, and Technical Stuff / Re: Opamps - Die pictures

« Last post by magic on Today at 06:22:15 am »

The circuit is not very complex and the complete schematic would be near but I somehow don´t like MOSFETs... 

Well, CMOS is annoying, but 30 year old CMOS is doable.

Turns out the signal path circuitry is quite simple, a few differential pairs and current mirrors are all there is to it. Looks like a TLC274 chopped into pieces and reassembled semi-randomly. The trick is auto-zero witchcraft and high DC gain achieved by a sequence of four stages with unusual compensation by two Miller caps and two input pairs. BTW, similar compensation is shown in datasheets of modern three stage CMOS opamps from TI like OPA172 or OPA1656; they call it "active feedforward" and I have also seen it called a "multipath" elsewhere.

The critical pairs gm1 and gm6 use striped common centroid layout ABBAABBA and their mirrors are ABBA. The offset compensation pairs gm3 and gm4 are oriented perpendicularly to output stage heat gradient but don't bother with common centroid. The other small stage gm2 is single-ended and the output stage is a simple rail to rail contraption: M56 sinks load current directly, M51 steals current away from current mirrors driving M55.

M58 is a dummy transistor in parallel with C1 which appears to compensate for capacitance added to C2 by M56. It isn't exactly identical to M56, but they must have made it work somehow.

2

Test Equipment / Re: Standardised Way To Test Oscilloscope Screen Update Rate

« Last post by boggis the cat on Today at 06:20:02 am »

I am thinking about the purpose of the refresh rate.

Perhaps the screen refresh rate is less important than the ability to display the waveform appropriately – so a waveform with a 'glitch' repeated at different rates could be used to test for this.

Would setting an AWG to generate a glitch at different rates be a way to verify that the 'scope is functional?

3

RF, Microwave, Ham Radio / Re: Transistor tester

« Last post by max-bit on Today at 06:18:23 am »

But I am surprised that so far no one has developed a "cheap" tester of TRANSISTORS, diodes, thyristors, thraics, with capabilities slightly beyond the "battery" values, so that Uce ~ 100V Ic ~ 1A etc.
It is even very difficult to find (if there are any) such devices from larger companies (but not costing xx k$)

Something in the range of a few hundred dollars to ~$1000

These "toys" have been on the market for many years for prices ranging from several dollars - a dozen or so dollars.

4

Manufacturing & Assembly / Re: Brief review of the Zhengbang ZB2520HL reflow oven (T-962A alternative)

« Last post by niebieski201 on Today at 06:16:17 am »

Hi.
I just collect my RF-A350 oven, I did not try any PCBs yet but when I checked build in reflow profile without any modifications and with thermocouples stick to bottom plate it doesn't look good.
Temperature in the middle is follow the profile but overshoot 5-6 deg. Temperatures 10 cm from middle, each side, seems to also follow profile but are under the line sometimes 10-15 deg, but within few extra seconds they starts following middle temperature.
Can someone share settings or other tweaks for this oven as factory one seems to be not perfect.

Attached factory profile 4 with empty tray.
Regards

5

Test Equipment / Standardised Way To Test Oscilloscope Screen Update Rate

« Last post by EEVblog on Today at 06:07:03 am »

As per this video at around 4:00




I'm thinking about a way to come up with the best and/or most easily test screen update rate (NOT waveform update rate).
High speed camera and frame anlaysis is one way obviously.
Comments invited.

6

Test Equipment / Re: Siglent SDS2000X HD, 12bit, 2GSa/s high definition oscilloscope serie.

« Last post by hpw on Today at 05:58:50 am »

Hello,

I have the impression that the SDS2000X HD always has a small downward dent in the left in channel 1 when the input is open in auto-trigger mode.


Best regards
egonotto

A good catch  IMHO it looks rather as a state ready issue (HW & SW), so samples to skip before as any good.

The other looks like "knocking on havens door" see picture as from Dave's video...  so any SDS2000X HD Plus revision to come...

Cheers

Hp

7

Computers / Re: Format a 256GB pendrive with FAT32 using a windows 10 pc

« Last post by IanB on Today at 05:58:31 am »

It's often overlooked that the Windows GUI is a graphical shell sitting on top of a command line OS.

This has not been the case for decades, since Win98.

No, I mean NT4 onwards up to Win 11. The graphical part of Windows is called "the shell", and the graphical APIs have "Shell" in their name. There are contexts where you can have a login session that does not involve the GUI, such as with services, batch jobs or remote logins. But more usefully, there are ways to access the underlying services of the OS from the command line, either with the traditional Command shell, or with PowerShell, and these invariably expose more options and allow more precise control than are available through the GUI.

8

Repair / Re: Commodore 1901 monitor repair

« Last post by scroeffie on Today at 05:46:01 am »

i have 3 of these ,first i would replace all purple caps they leak and most are out of spec .did you replace the front rifa cap they wil explode
also chek the voltage regulator .these monitors also have allot of cold solder joints reflow everything .remove all old glue
chek front switch sometimes they are dirty
i just done the scart rgb mod works perfect 

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Projects, Designs, and Technical Stuff / Re: Practically smallest SMD size for assembly run of 1 to 100 pieces by PCBWay etc

« Last post by charliehorse55 on Today at 05:44:28 am »

How small does it need to be? I use 0402 as standard for passives, never had a problem with it. I just ordered a board from them with ~600 components per board, had 3x3mm 9-pin QFN,  SOT-23, and a few different ICs with 0.5mm pin spacing.

They have x-ray inspection available for BGA and other high pin count devices, but normally they rely on optical inspection. It works quite well.

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EEVblog Specific / Re: EEVblog 1612 - Siglent SDS1000X HD 12 bit Oscilloscope Teardown

« Last post by EEVblog on Today at 05:43:14 am »