Recent Posts

81

Repair / LEM Baby Echo Mixer Amp Issue

« Last post by uslrs on Today at 10:33:58 am »

Hi All, I'm restoring this LEM Baby (built in the 1970's) and there has been a major issue with the power amp and repairs carried out at some point in the past.  I've been unable to find a schematic, only one for a later version which has an IC in the first stage and has a complementary output pair, which mine hasn't.  I've produced a schematic (attached) from the pcb but most of the transistors are unmarked and I'm not sure whether they are original or replacements.  I'm struggling to make any sense of this design so would much appreciate any help or information which might enable me to get this power amp working.  I've attached a notated photo of the pcb components to identify the transistors in the schematic. Hoping someone recognizes this and can provide some information.  Many thanks.

82

Other Equipment & Products / Re: Pace ADS200 soldering station

« Last post by pope on Today at 10:33:39 am »

Does anybody understand what the "improvements" actually are?

"We won't admit we screwed up the original performance spec"

This.

83

RF, Microwave, Ham Radio / Quansheng UV-K5(8) firmware modding

« Last post by radiolistener on Today at 10:30:53 am »

just bought Quansheng UV-K5-8 radio.
I want to play with custom firmwares with AM/SSB and spectrum view.
But first I want to backup factory firmware and calibration data. But it's not clear, how to do it on linux?

I read that on windows it can be done with k5prog-win which is designed for Windows and is based on k5prog which is available on linux.

Tried k5prog:

Code: [Select]

$ ./k5prog -r -v
Quansheng UV-K5 EEPROM programmer v0.9 (c) 2023 Jacek Lipkowski <sq5bpf@lipkowski.org>

k5_prepare: try 0
cmd: 15 05 ok:1
******  Connected to firmware version: [2.01.32]
Successfully read EEPROM

It wrote k5_eeprom.raw file with size 8192 bytes. But I'm not sure is that eeprom file contains calibration data, or is it needs to be read with different command?


And I don't see the option in k5prog to read exiting firmware from radio. In documentation it has option -b to write firmware, but I want to read it from the radio. Is it possible?

84

Test Equipment / Re: Owon DGE2035 DGE2070

« Last post by 5U4GB on Today at 10:30:19 am »

As a followup, I've posted a slightly longer writeup, along with some thoughts on why the output voltage increases with load, here.

85

Other Equipment & Products / Re: Dymo 550 Thermal Printer DRM Hacking

« Last post by js_12345678_55AA on Today at 10:30:13 am »

It kinda works on newer SN models. It does detect emulated roll now.
But the issue is that it remembers. Number of labels decrease and do not reset after a power cycle. Not even when testing on another PC.

It sounds like they might use internal memory on the STM32 now to store the counter of a roll UID...
But I'm pretty sure they do not have unlimited memory for this and as a wild guess I would say they only remember that last <10 UID.

In the source project we already have several UIDs which we can use to alternate and switch between.
Can you make the following test please:
* setup roll in emulation, do some decrements, switch off, switch on ==> counter in emulation resets and the printer should be in your reported "blocked state"
* now change firmware and select different UID for emulation. In main.c source file change the line:
    #define SLIX2_TAG_EMU 1  // 1-12
   and use a different value (e.g.  2 )
* check if printer works again, decrement some, switch off, ==> counter in emulation resets and the printer should be in your reported "blocked state"
* now... change in firmware back to emulation of tag 1
  => check if printer works again
    + if it works, they only remember the last tag ... easy fix
    + if it does not work, they might remember multiple tags... but we have more good tags for emulation.
       Unfortunately the only way to find out is to try them all one by one and always checking if emulation of tag 1 is coming back to live

In case we can find that they only can remeber a limited number of tags, we could add cycling through our known good tags to defeat this.

JS
   

86

Beginners / Re: Switching a 3KW (240V) immersion heater: Solid state or mechanical relays?

« Last post by 5U4GB on Today at 10:27:19 am »

driving a higher-power contactor like the Finder 65's that people have recommended,

A followup question about this, the usual-suspect electrical suppliers, meaning ones who provide the necessary SDOC, can only provide the 2xNO with a minimum order quantity of five while they have 1xNO, 1xNC in stock in single-unit quantities.  If I source it myself from Farnell or whatever it won't come with an SDOC.  Given that I'm only switching a pure resistive load that heats water rather than, say, turning limb-removing power machinery off, so even if contact welding occurs it's no big deal, is it worth going to the 2xNO supplied-by-user to switch active+neutral or is it good enough to use the 1xNO with SDOC to switch active only?

Also, am I overthinking this? :-).

87

Beginners / Re: Power supply output transistors

« Last post by xavier60 on Today at 10:26:31 am »

This project happened near to 6 years ago.
This is a version I had drawn that's simply driven by Pots, for anyone wanting to experiment with it.
There may be no simple way of implementing a simple linear regulator that also works properly.
The other option is the BJT design I used in a 5A PSU which may be able to be beefed up with more output transistors.
How many, I can't say for certain, at least 4 with a pre-regulator.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

88

Repair / TEK 475A VOLTS/DIV compensation problem

« Last post by fabio.deangelis on Today at 10:25:25 am »

Hello EVVBloggers,
I have recently restored an old TEK 475A oscilloscope bought on eBay for a few Euro. The main problem was a faulty high voltage multiplier and a bad electrolytic capacitor on the +15 volt rail. Another issue was the “blocked” fan cooler that I have attempted to restore by replacing a faulty U1690 with four transistors and grease the motor. The fix apparently worked but unfortunately the fan motor did not start at power on all times. I had to make an agonizing decision, replacing the sophisticated Tek fan motor assembly with a small computer fan, attached to the +15 volt with a resistor ☹
The scope is now working very well in all functions but a weird issue in the VOLT/DIV compensation. I am unable to compromise the compensation among the 0.1, 0.2 and 0.5 Volt positions. Once I compensate the 0.1 position (C32, C33 if I remember correctly), then I got a bad image (under compensated) on 0.2 and 0.5 positions. If I re-adjust C32,C33 for a flat square image on those positions then I got a bed image (over compensated) on 0.1 volt position. The problem is present on both channels, even if it is more evident on CH1. I believe I have successfully performed the vertical calibration steps present before the VOLT/DIV compensation adjustment. I did a test by replacing the “compensator unit” (C32 C3) taken from another 475 , but the result is unchanged. Note that I have thoroughly cleaned the attenuator switches, which appear to work well.
Any clue what could be the issue here ?

89

Repair / Re: Capacitor has different readings if stored upside down

« Last post by TERRA Operative on Today at 10:23:47 am »

Turn them back over so they are sitting upright for a while and test again to see what they say.

90

Microcontrollers / Re: Signal filtering - Could this work ?

« Last post by gf on Today at 10:21:18 am »

The CIC filter already does the moving average ?

A CIC filter is just a particular way to implement a 1st order or higher¹⁾ order moving average filter. A CIC structure is particularly useful in combination with down- or up-sampling.

I think that the first that have to do it's take long raw measurement from field and then find out best math (filters/DSP/etc), that will solve your problem (with something like MATCAD). And only after this start to implement algorithms in firmware.

  I wanted to suggest the same. Collect at least a few minutes of data (or better an hour - even that's only 1.44 million samples @400Sa/S), and analyze it first.

And try to specify requirements like
- What is the desired accuracy / uncertainty?
- Do you want real-time display for instantaneous fill level and instantaneous weight loss per second?
- How much settling time / delay are you willing to accept?


1) An N-th order moving average filter is a concatenation of N equal 1st order moving average filters. Just send the output of the 1st stage into the next stage, and so on. It's also called sinc^N filter, which refers to the shape of the magnitude of the resulting frequency response.