Recent Posts

1

Microcontrollers / Re: STM32H7 CortexM4 USART DMA issue

« Last post by Silenos on Today at 04:31:16 pm »

What's "RTS"? How it "does not work"? What are DMA registers values and what they mean? Did you set DMAMUX?
Also at least some H7s have botched USARTs which hang after some time when used with DMA. You have to flip certain undocumented magic bit to make it work, it is described in some errata.

2

RF, Microwave, Ham Radio / Re: High bandwidth FM signal generation

« Last post by ejeffrey on Today at 04:27:22 pm »

The xilinx RFSoC dev kits are the usual thing people use when the commercials available SDRs run out of  bandwidth.  The dev boards cost about $10-15k, but give you several channels of several GHz depending on the model.  They also have a "mix mode" where the DAC output can be chopped by the clock to put more of the power in the second Nyquist zone.  That can allow you to cover 0-8 GHz with no external mixer.

It's a fair bit of development work to get it to work compared to an SDR or off the shelf instrument but there are pretty good examples / documentation and they are supported by the Pynq project although I havent used that so I don't know how well it works.

3

Repair / Tektronix DM501A repair

« Last post by Rax on Today at 04:26:57 pm »

Working on a few units I got, hoping to put together one or two fully working if the other ones may become parts harvesters.

They all have slightly different signs of trouble, but essentially nothing works well, starting with non-sensical display annunciations. I'll stick with one particular unit for now to not confuse the conversation with inconsistencies.

Unit #1, hence, exhibits this inconsistent display of measurements. Typically, applying a certain excitation would change the screen somewhat, but information displayed would still be inconsistent and hard to interpret.

Here's some data I collected this far on this particular unit:

• The core voltage measurement stages are not working well (as I assume all other measurement modes boil down to this). I've followed the troubleshooting tree for DC voltage and I see no voltage present at U1601-pin15.
• In checking the clock, I enclose what I'm seeing at the base of Q1435 and the OSC input of U1603-pin8.
• I reseated the display board (access is quite tight, so I didn't pull it completely out, just enough to be able to apply some deoxit to the board pins and then pushed it back in.
• The PS rails seem to be close enough.
• I haven't checked the electrolytic and tantalum caps on the board, but given the health of the rails, I am not prioritizing these at this time.
• I reseated all ICs on sockets. To flesh that out a bit, I pulled them, sanded the pins a bit with an abrasive pen, cleaned them with IPA, then applied a touch of Deoxit with a swab.
• I've resoldered Q1415. Its solder points seemed to be pretty severely starved from solder.
• Access is not easy, but I've parsimoniously washed the switches with Deoxit. In hindsight, maybe I should have just tried an IPA wash first, particularly as that's less risky in terms of contamination. So maybe I'll give it another go with IPA on the switches, and seek to limit contamination with Deoxit oils on everywhere else than the inside of the switches (which will not be easy, I don't think).

The troubleshooting tree for DC Voltage is not too clear to me. For instance, what to do in case the U1601-pin15 levels are wrong (or non-existent).

4

Repair / Re: Rohde Schwarz CMU200

« Last post by Harry_22 on Today at 04:26:45 pm »

Please remove the modules 1135.5206.02 as well as 1100.2400.25 and place burned part areas in the center of photo. The burned parts are seen on both sides.

5

Projects, Designs, and Technical Stuff / Re: (Yet Another) DIY Multislope ADC

« Last post by NNNI on Today at 04:26:09 pm »

Thanks for the example calculation, it was very insightful.

There is always the option of running the RP2040 without a PLL from an external 48MHz clock (which would also work out in terms of timing, 48MHz is exactly half of the 96MHz I chose for the previous code). I am not sure if this would yield much improvement.

Would I be right in assuming that the faster a logic IC is meant to be clocked, the lower the jitter? For example, the SN74LVTH273 [1] can be clocked at up to 150MHz. The latch can be clocked from the same oscillator that is feeding the RP2040, that might help with synchronization issues.

[1]: https://www.ti.com/lit/ds/symlink/sn74lvth273-ep.pdf

6

Repair / Re: Help needed identifying a Zener/TVS Diode (Toyota ECU)

« Last post by fzabkar on Today at 04:25:32 pm »

This vendor rates it at 27V 3W, if you can believe it:

https://www.lazada.vn/products/voltage-regulator-s5225-zener-3w-27v-thao-may-test-ok-i2423357599.html

Here is a discussion about a circuit that uses this diode:

http://www.subaru-svx.net/forum/showthread.php?t=59362&page=2

The diode appears to be D4 in this circuit diagram (D4 is a place holder):

http://www.subaru-svx.net/forum/attachment.php?s=76c57ef43ebf18a1041f22109cc5937f&attachmentid=16095&d=1331498282

The IC (μPC1251) in that diagram has a maximum supply rating of 32V:

https://www.renesas.com/us/en/document/dst/upc1251-upc358-datasheet

7

Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by sw_guy on Today at 04:25:16 pm »

I have never understood replies like tggzzz. Nothing valuable to say, full of negative load. Waiting for missing parameters. Oh well...

Suggested reply for the next time:
"It depends on the frequency response, output voltage and drive capability. Please give us more detailed specifications in order to give exact opamp examples. However, in general, I can say that typical opamps used for low-frequency applications, which are the common use cases for wien oscillators, are for example LT1632, LT1013, LT1001".

or.... just ignore the question.

br,
sw guy

8

Projects, Designs, and Technical Stuff / Re: role of optocoupler for biasing drain of amplifiers

« Last post by john23 on Today at 04:21:52 pm »

Hello XVR, in the case below i conected two power amplifiers.
each of them needs to be 20V and 6A , and i get them by tuning the system with Vgs and Vds.

Is there a way to improve the circuit so my Vds  of the power amplifier could be tuned ?


Thanks.

9

Beginners / Re: LM324 Power Supply with variable voltage and current

« Last post by xavier60 on Today at 04:19:17 pm »

Do you mean that I need a separate winding on the transformer or another small transformer for the DVM and tap changer ?

That can be ambiguous, you can have the same winding or transformer for the tap changer and DVM but separate to powering the LM327.

10

Beginners / Re: What function generator, that does a bit more than just a simple signal

« Last post by radiolistener on Today at 04:17:15 pm »

Or maybe it's possible using arbitrary waveform, but I've never tried that.

Can you please check if my tool to read/write arb waveform for PSG9080 works with JDS2800?

just connect it to PC and try to execute:

Code: [Select]

PSG9080_ARB.exe COM3 -read 1 wave01.txt

where COM3 is a port which appears when you connect signal generator to PC.

It should read arb wavform 1 from generator to "wave01.txt" file