Recent Posts

21

Beginners / Re: 72C5 - What Is This?

« Last post by Trurl on Today at 08:19:43 am »

The photo above shows the side(auxiliary) board of the PSU with one of the "72C5" parts towards the center(use slider at bottom of this post to move to the center of the photo). I've marked the connections as follows;

Pin 1 (Blue) :    Adjacent via connects to Microchip dsPIC33FJ64GS606 pin 26 (VDD) (towards the right side of the photo)
Pin 2 (Yellow) : Connects via resistor "91B" to the LM393 opamp's pin 5("+" non-inverting input)
Pin 3 (Red) :     Via connects to the +12VDC main output of the PSU

Thanks in advance... Cheers...

22

Beginners / The old "Replace blue LEDs with red LEDs" 7 segment question (74HC595)

« Last post by trondl on Today at 08:18:51 am »

Hei from Norway!
I'm posting it here in this section as I'm a n00b in the technical sense when it comes to LEDs and current limiting.

I have an older (2011?) Mytek USB-DAC with seven blue 7 segment displays that after the years have gotten dimmer on the most used segments (48 kHz...), making it look like "burn in".
Is this evidence of early blue LEDs wearing out faster?
The unit has seen 24/7 on highest brightness.
It is dimmable, and on the lowest setting, the LEDs are somewhat similar.

I have gotten access to the front panel parts and layout document from the company, but not the schematics.
The unit is seeing too much usage to give it downtime for poking around yet.

What I can see is that the thru-hole 7 segment LEDs are Lite-On LTS-2801AB (3.8Vf @ 20mA If, common anode).
They seem to be controlled by a 74HC595A per segment and have a 220ohm current limiter per line.
Since the Vf is 3.8, I believe the 595 is running at 5Vcc.
Could this also be a symptom of failing Shift Registers? Doesn't quite seem logic to me (pun?).
I've heard rumours that a 74HC595 isn't ideal for driving LEDs, and can wear/burn out.
Also, how does dimming work on a 595?
PWM?

LTS-2801AB is obsolete, and I'd wish to replace them with the red LTS-2801AP (2.1Vf @ 20mA If) which is still somewhat available, or an equivalent.
I have a hunch that red LEDs last longer, and I prefer them for not being so intruding on the eyes (who doesn't?)

I've tried to find other alternatives, but the physical size seems to be a limiting factor: (h)10mm x (w)7.4mm x (d)6.1mm.
Is there a "standard" size for 7 segment displays?

Now, the main question of course, can red LEDs with ~2Vf last longer than 2 seconds in this circuit?
3.3V seems to be available on the PCB for driving an IR receiver.
Run the 595 on 3.3Vcc instead?

Thanks in advance for your time and input!

Mvh
Trond

23

Other Equipment & Products / Re: Miniware MHP50

« Last post by SteveyG on Today at 08:17:39 am »

Apologies for the long delay, I've release the video on this finally.
It took a while for my PD3.1 power supply to arrive, but it works well at 28V

24

Test Equipment / Re: SDS800X HD - Issue disscusions - is it me, or the scope?

« Last post by ebastler on Today at 08:09:15 am »

We are blue in the face from telling such, so much so I think ears must be just painted on.

How is this type of comment supposed to be helpful? It's only stoking up controversy. Please bite your tongue and refrain from posting such insults.

25

Metrology / Re: ADR1001 - Ovenized Voltage Reference System

« Last post by iMo on Today at 08:08:51 am »

Milpitas list..
I see there only two parts usually discussed here - LTC2057 and LTC665x..

26

RF, Microwave, Ham Radio / Re: RF 2.4GHZ through Via

« Last post by 24602 on Today at 08:08:28 am »

Haven't measured it but if TX RX antennas are right next to each other there's basically no reception.

27

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Fungus on Today at 08:07:51 am »

its should be possible to look at near 1GHz RF, such as 433 or 800MHz china RF module digital ASK modulation

Which I would never want to do...

28

Test Equipment / Re: SDS800X HD - Issue disscusions - is it me, or the scope?

« Last post by ebastler on Today at 08:06:25 am »

What was also confirmed by many others are many false alarms and errors you made and then blamed scope . That is why we say a methodical approach is needed and good detailed explanations are needed.

For instance, you NEVER write what FW you are running at the time you encountered something that is suspicious behaviour or bug.

So in few weeks from now, when stuff is fixed nobody in the world will know if all the stuff you reported is still suspicious or that was some old initial FW that is not relevant anymore.

Like I said before but it fell on deaf ears.
You can stop writing about bugs, looking for them, or investigate them at this moment.
You are wasting your time (and ours if we decide to read).
There is imminent FW release being tested, as we speak.

Wait for a bit until new FW comes out.  Then start first with all the stuff that was reported in release notes that will come with it, then all the stuff that was reported and you don't see them in release notes.

This is my advice to you. You don't have to listen, of course.

You are too harsh with eTobey, I think. Yes, there have been "false alerts", but a surprising number of actual bug findings too. And this thread is titled "is it me or the scope?", so what's wrong about bringing up potential issues where one is confused and wants to ask others for help to clarify the situation?

Firmware version is 1.1.3.3. throughout -- what else would it be for mere mortal users?   But I do agree with you that a bit more detail about the signals and settings would be helpful in many reports.

Regarding the upcoming firmware, you are quite bullish in your advice that "it's likely to change everything, you can stop looking for bugs for the time being". Have you tried with the two three most recent bugs (#14 to #16) which eTobey found over the past two days, and which electronics hobbyist has added in the SDS800X HD bug thread?

29

Repair / Re: HP 16700/16702 Power supply repair

« Last post by FrodeM on Today at 08:04:56 am »

Not sure if you figured it out, but it's a TOP227Y switching controller. You can see the schematics around this part here:
https://bitsavers.org/test_equipment/hp/167xx/Celestica_7000_Aux_Power_Regulator_Schematics.png

Note that 360V might not be correct. I have since figured out that the high-voltage side is generated by a boost-converter regulator, not just rectified power-grid voltage. It is more likely something like 400V, but I have not measured it. Also make sure to check D7 down at the main board, this is by far the weakest link in the main current-path of the PSU.

30

FPGA / Re: If Lattice iCE40UltraPlus has DDR primitives like ODDR in Xilinx?

« Last post by SiliconWizard on Today at 08:03:13 am »

I don't think they do. Haven't seen any mention of that in the datasheet nor in other docs.
And keep in mind these are cool, but relatively "slow" devices. I/O buffers are rated 250MHz max. (Above 2.5V for outputs, less otherwise.)
So if you're hand-implementing DDR, your data rate may be much lower than you'd otherwise expect from DDR RAM. That said, its logic blocks wouldn't take high enough Fmax for it to make a difference anyway.
Using DDR RAM with an iCE40UP sounds a bit odd - what's your use case?