Fake chips!

So, as part of my VFD project, I’ve been purchasing various ICs from eBay (almost always from China, because they are always the cheapest!)

I’m used to counterfeit ICs turning up from time to time, but I’ve run into the same counterfeit IC (with the same ‘batch number’), and the same problem from a couple of eBay suppliers, so I thought I’d share the issue here.

The IC is a SN74HC595N – a fairly simple 74 series shift register, in a 16-pin DIP form factor.

However, it doesn’t work as advertised.

It’s labelled SN74HC595N, with a batch number of GM1807FSF E4. It is allegedly from TI, but I very much doubt it.

It was keenly priced, at around 5p per IC for a batch of 500 chips.

It is indeed a shift register, but instead of having the tri-state outputs it should have, it seems to have open-collector outputs, like a 74HC596. So it is not usable in my application.

I did find that I’m not the only person having this problem – https://translate.google.com/translate?hl=en&sl=de&u=https://www.mikrocontroller.net/topic/463936&prev=search

Sigh.

One of the sellers has refunded me without too much debate, but I’m still arguing with the other…

IV-11 VFD Clock – Assembly instructions

Introduction

Tools required

Fine point soldering iron (temperature controlled recommended)
Multimeter capable of measuring low- voltage DC (1-40v) – you will need this to set up the boost/buck converter boards
Nail varnish or similar – idea

USB socket

Insert the USB B socket onto the LOWER side of the board, and solder its’ four data pins and two retaining lugs.

Programmable LEDs and IN4148 diode


Install the programmable LEDs on the UPPER surface of the PCB. Note the polarity carefully, as shown below. Each LEDs’ polarity is ALTERNATED – be careful to get the LED orientation right. Try to get them as vertical as possible.

Don’t mount the LEDs flush with the surface of the PCB – leave a gap of around 4mm, as shown below:

Next, insert the small signal diode on the LOWER side edge of the board, ensuring that the black line on its’ body faces the same way as the white line on the PCB silkscreen (photo below shows diode the right way round before laying flush with the board and soldering in to place.


The diode correctly soldered into place:

At this point, connect a USB B cable to the USB socket, and plug in to a power source (either PC USB socket, or a USB adaptor etc). All the LEDs should light up blue.

Install 1.5v low voltage buck converter


Break off four individual pin headers from the pin header strip supplied, and solder them to the pin holes in the buck regulator board as shown below:

Then, install the converter onto the LOWER side of the PCB in the location marked 1.5v for headers U18. You may need to angle/bend the pins to line up with the board holes. Once inserted, solder the pins into place from the UPPER side of the board (shown in place below):

Install 25v high voltage boost converter


Solder four individual pins into the holes in the boost converter, then install it onto the board as shown below, and solder the other end of the pins in to place.

Setting the voltages

Next, apply 5V power to the USB-B socket, and use a multimeter and small potentiometer-adjustment screwdriver to set the voltages for the buck/boost converters.
For the boost (high voltage) converter, the gold screw on the blue potentiometer should be turned to set the voltage on its’ V-OUT pin to 25v.

For the buck converter, the potentiometer should be adjusted to get 1.5V (+/- 0.15V) on its’ V-OUT pin.

Once these potentiometers have been adjusted correctly, a small dot of nail varnish is useful to stop them from moving again.

Install the real-time clock module

Bend the 6 pins already installed into the RTC module so they point straight down (away from the board), and solder 4 pins from the supplied pin header strip into the four vacant holes at the other edge of the board, as shown below:

Then, install the RTC module and solder in to place:

Install the push switches and resistors

Insert the four pushbutton switches into place on the LOWER side of the board and solder them into place.

Then, install the resistors into place: (they can be installed either way round)

R1-R4 are 10K ohm resistors (colour code brown black orange gold)
R5 is a 22k ohm resistor. (colour code red red orange gold)
R7 and R8 are 4k7 ohm resistors. (colour code yellow violet red gold)

Install the shift register and VFD driver integrated circuits and decoupling capacitors

Insert each of the integrated circuits into their footprints on the lower side of the board. The 16 pin chips are the shift registers (74HC595) and the 18 pin chips are the VFD driver chips.

Note that they are inserted the right way round – there are small markings on the silkscreen which must align with the notches on the chip. The 16 pin chips have their notches facing AWAY from the USB socket, and the 18 pin chips notches face TOWARDS the USB socket. When soldering, it is a good idea to solder a few pins on each IC to anchor it into place, then move on, and come back to solder the remaining pins, to avoid overheating the ICs.

The decoupling capacitors can be installed either way round, and one sits adjacent to each of the shift registers:

Install the WeMos D1 and pin headers

In the WeMos packaging are a pair of pin socket strips (female) and solder these into place on the lower side of the PCB.

Solder the male pin header strips to the WeMos board as shown:

Then, push the Wemos onto its’ pin headers, so it sits like this:

Test of Wemos and LEDs

Apply 5V to the USB B socket again. You should now see the LEDs illuminate with a rainbow effect.

Install the VFD tubes

Errata

On PCBs marked V1.1 (version is printed under the WeMOS D1):

You need to use a small length of wire to connect the ground pins of switches 2, 3 and 4 to the ground pin of switch 1.

As shown below, use small lengths of insulated wire to connect the pins marked by red circles to each other.

On V1.2+ boards, this is not required.

Repairing a BT Baby Monitor 250 Power Button

My BT Baby Monitor 250 has a faulty power button as a result of toddler ‘droppage’.

The power button requires hard pressing and no longer has the ‘click’ it used to. It also doesn’t always reliably turn on at all.

Time for a repair!

Dismantling it!

Step 1

Remove the battery compartment cover, as well as the batteries.
Along the bottom edge of the compartment are a pair of phillips screws – remove these.

Step 2

The two part case is now held together by a pair of snap-together clips on each side. These can be opened with some judicious levering. The catches are shown here, circled in red: (case removed for clarity). Levering the case outwards at these points will help to release them. The case halves can then be separated.

From the side:

Step 3

Gently lever out the pair of plastic clips holding the LCD to the printed circuit board.
It then lifts off, and hinges downwards.

One clip is visible here:

Step 4

Remove the two small phillips screws under the LCD holding the PCB down

Then, remove the screw at the bottom of the PCB.

Step 5

Gently fold the metal contact terminals that stick out through the bottom of the case inwards, and carefully prise the circuit board free from the case. (These are visible in the picture above)
You might want to remove the vibrate motor from the bottom half of the case (it’s just press fit) to get more wiggle room.

Find the problem

On inspecting the surface-mount power switch, it was apparent that its’ two securing lugs at the front had come loose from the PCB. They were originally soldered, but the solder has fractured, leaving both the pads and the tabs intact.

I simply resoldered these to the board, and quickly resoldered the joints on the two contacts at the rear of the switch to make sure they had good contact to the pads.

Reassemble

Reverse the above steps to reseat the PCB into the case, resecuring it with the three screws, (vibrate motor as well if you removed it), then refit LCD back into place.

Check at this point that all the buttons have a normal ‘click’release’ feel to them, (if not, sometimes the little plastic sticky foam pieces on the end of the plastic ‘button pressers’ have come adrift…)

Then snap the case back together, seating the top part first. Replace two screws under battery compartment. Refit batteries and test.

Done!

Delonghi Perfecta machine fault – no steam!

I was given a machine from a work colleague to fix (a snazzy Delonghi Perfecta bean to cup machine) which wouldn’t froth milk or generate steam but did make coffee.  When asked to steam, it just displayed “Heating Up…” then returned to the main screen.

I guessed the steam boiler element had probably failed open circuit, so opened the machine up, and checked its’ resistance with a multimeter (which was around ~50 Ohms), so that wasn’t the problem.

The boiler element is protected by a pair of thermal cutouts, which will permanently blow (open circuit) if the element overheats to prevent a fire.  Both of these had failed.  So I thought that buying a new pair of these would solve the problem.

Then I found this article detailing a similar fault, where the triac which controls whether the element is on or not fails closed circuit, meaning the element overheats and blows the thermal fuses.  That article discussed the triac powering the main boiler rather than the steam boiler, but both are driven the same way.

This seemed to make sense and would explain why the thermal fuses had been blown.

Testing (carefully!) with the multimeter, I found that the element was continuously powered with full AC voltage even when the machine was on standby, so it became clear that the triac had failed closed circuit in this case.

So, to fix the machine, I replaced the two thermal cutouts from 4Delonghi: 2933924OH

and the triac (from RS): Part No BTA24-600BW. From RS, it’s 6871029

 

and everything worked happily!

Here are a few photos of the repair:

The horseshoe-shaped steam boiler (behind the back cover of the machine). You can see one dangling thermal fuse which I’d unbolted, the other at the centre of the image, and the two terminals of the boiler element. Both fuses are wired in series with the element – one in series with the triac-switched feed from the control board – lilac wire, and the other in series with the neutral return (brown wires).

 

 

 

The control board, with the failed triac indicated with an arrow.  The one on the other side of the heatsink controls the boiler for the hot water. (and can fail in a similar way!)

 

Faulty triac closeup (arrowed)

 

The resoldered and re heatsink-compounded triac on the main circuit board prior to reinstalling the retaining clip and reassembling the machine.