Retell.IT – 2011 – Samsung HT-TZ315 Home Theatre System

Going through my repair books, I came across an interesting repair that I did in June 2011. It is now time to “retell.it“. I had purchased a Samsung HT-TZ315 Home Theatre System a few years earlier – it was a good price, and performed well, however I noted at the time that the display was a little dim. I didn’t think much of it at the time since everything was working fine. Fast forward to June 2011 – one day, we went to use the home theatre and the blue power light came on, but nothing from the display. The display just would not light up – but we managed to use the remote control shortcut buttons to prove that the home theatre system was indeed working – just nothing being displayed.

Ok, most faults like this are usually power supply related – I thought. The display panel uses a VFD, a Vacuum Fluorescent Display, so most likely the power to the VFD on the front panel must not be working. I removed the home theatre from the tv cabinet, disconnecting all five speaker cables, plus the optical and hdmi cable etc. After opening the box, I looked at the power supply and fortunately, the voltages are screen printed on the pcb – fantastic.

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I used my multimeter to check the voltages on each pin concentrating on the vfd power – and all pins had voltage on them. Although the vfd pins were not quite +4.3V and -4.3V but were +3.2V and -30.1V – I thought that it might be fine.

I also checked the ESR of the capacitors and mostly were ok, with a few that I consider a little borderline. I proceeded to obtain replacements for those that I did not have in stock, then replaced them. After doing this, I retest the home theatre and still no display – sound was working, volume was working, just no display. From a search on the internet, it seems that problems like this require replacing the front panel pcb – AH41-01100A. From what I could find, the only replacements at a reasonable price was from the UK at around 40 pounds, ouch – not cheap when converted to AUD.

Ok, why not check the front panel pcb, maybe there is a broken track somewhere – a long shot because a broken track usually means something burning out, which is usually accompanied by other problems that would be visible. Anyway, removing the front panel pcb was eventually accomplished – need to remove a few other cables in order to get it out.

Tracing the power connections around, I eventually got to the VFD and interestingly, could not measure the VFD voltage – so there was a broken track or a dry joint.  I used a 10x magnifier and went through all of the pins attached to the power connector and where they go to, no dry joints seen. Turning it over, I could trace connectivity from the power sockets to all of the pins – what gives. After scratching my head a while, and turning the board over and over, I eventually noticed something that was slightly unusual. Two pins on the VFD were a little bent – ok, most pins should be straight since these are inserted in the factory during manufacture, but two pins, which coincidentally were connecting to one of the power circuits – the -VFD pin. When I put the multimeter probe on the pin, of course I push down, and it makes contact.

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What seems to have happened is that because the pins were slightly bent when the VFD was inserted during manufacture, over time, together with transport, the solder pads on these two pins had lifted from the circuit board. Looking from the bottom, all the joints look fine, but using a 10x magnifier, I could see a gap between the soldered pin and the circuit board. I took a photo of it to show that I was not dreaming.

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Here is a magnified image, you can see the right two pins have a slight dark area under the solder, this is the gap – compare with the other pins on the left where the solder pad merges well with the board. Resoldering the two pins, and reconnecting the front panel pcb – and voila! I get a display and had saved ordering a replacement board from the UK. It is also brighter than it had been originally.  The lifting solder pad had produced a dry joint that was high in resistance, but enough so that it would pass inspection since it was lit, but eventually the resistance increased due to the pad continuing to lift, until it went open circuit.

Now, three and a half years later, this same home theatre system is still working well.  You may also think, how could this happen.  These home theatre system can get reasonably hot when driving all the speakers.  This heating and cooling cycling will cause metals and plastics to expand and contract at different rates – because the pins were bent, it acts like a little spring that pushes and pulls each time the system in on and off, eventually the solder pad lifted enough that no power was going to the VFD.  The forces involved are very small, but over a period of time, like 2-3 years, it all adds up.  In addition, with a sub-woofer in close proximity, this may also cause the display to vibrate, and this would just make it worse.

Reupholster.IT – Foot Stool

This morning I woke up to a dreary cloud-covered rainy sky.  What better to do than something indoors.  I have a foot stool which has seen better days.  It has brown feet, so it was time to “reupholster.it“.

My son plays Warhammer 40,000 and had some brown snakeskin vinyl left over.  I decided to use this to reupholster the foot stool.  I also added some foam that I had lying around that I was able to fit to increase the cushioning.

A few days, I had removed the old vinyl and removed the numerous nails that had been used to upholster it originally.  The stool had been hand made – probably by my father many years ago.  I will use a staple gun to fasten the new vinyl.  The usual way is to staple one end of the stool first, with a few staples, then stretch the other end over and do the same.  Then the sides are done similarly.  Once the new vinyl is in place, it was time to trim the vinyl to an appropriate size.  Then fold the corners and staple in place, then to finish the vinyl, add additional staples – which help to spread the load and reduce the chance of the vinyl tearing at a staple.

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Finally, to re-attach the feet.  The photo shows the end result, together with the original vinyl.  Looks like new, now and now the feet are matching colours.

[NOTE] It doesn’t take very long to do, and we have also reupholstered a number of dining table chairs when the fabric starts to wear.  Some simple tools like a staple gun, utility knife, scissors, pliers are really all that is needed.  One of the chairs that I had reupholstered a few years ago, had cracks in the plywood base, so I had to make a new base and needed to use a drill to make the keyhole – but that is another story.

Recap.IT – Aldi Vivid 32″ LCD TV

One of these Aldi TV’s came in – a Vivid 32″ LCD TV with a problem where the screen display goes out from time to time. I had seen it happen a couple of times, and could see that it was the backlight that was the problem. However, the backlight circuitry appears to be working fine most of the time, so the fault could be due to the power supply.

The power supply is a Megmeet MP-116A – a search of google shows that a lot of people have had problems with this power supply. Also searching for Vivid 32″ shows some similar faults but no real fix.

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I checked most of the electrolytic capacitors, they all appear to be within tolerance as far as ESR is concerned. ESR or Equivalent Series Resistance is a measure of how well a capacitor is working, in addition to its capacitance. Power supplies tend to get quite hot, and when capacitors get hot, they can start to dry out – and noticeably it’s ESR tends to increase, until eventually it is unable to filter out any ripple currents effectively.

I also used an oscilloscope and looked at the 12V output of the power supply – it was showing some 200mV of ripple, not a lot but could be causing a problem if the ripple increases during higher loading.  The large main capacitor ESR was not high, at 0.66 ohms, but usually this is one that would go first.

In any case, it is usually best to “recap.it“, i.e. replace all of the electrolytic capacitors – so this is what I did. I got the parts yesterday and replaced them today. After removing the parts, I also checked the actual capacitance and found a couple that appeared to be slightly low, but most were within tolerance. I will test it further during the weekend and see if the backlight fails again – if it doesn’t, then it could be that replacing the capacitors in the power supply did the trick.

[NOTE]  The replacement 68uF 450V main capacitor as a comparison had an ESR of 0.2 ohms – this means that its power dissipation for ripple currents will be considerably less than the original capacitor, and hopefully run cooler.

Reinstall.IT – Dell OptiPlex 980 Desktop

Recently a Dell OptiPlex 980 Desktop came in for me to look at. The hard disk had been formatted and the Dell Recovery CD was unavailable. The case had a Microsoft Windows 7 Professional sticker on it with the code still readable in spite of having “DEAD” written on it in Red texta.

This desktop has an Intel Core i5 processor with 4GB of ram, a fairly reasonable machine manufactured in 2010. I booted with a Ubuntu Linux CD and had a look at it first. I could see 4 partitions, one of which had been formatted with nothing on it – that would be the reason for booting up with an error about missing files. This also confirms that the desktop will boot and that the hardware is working.  It was time to “reinstall.it“.

I had on hand a Windows 7 Professional install DVD. I was interested in whether or not, I could use this to install – so the best way is to just jump right in.

Booting up with this 64-bit install DVD, you get a prompt to upgrade or perform a new install. I chose a new install, then when prompted on the destination, I clicked on Advanced and deleted all existing partitions first, then chose to continue. This then would set up the disk partition as Windows would like it, and without the Dell recovery partition. I let this continue until it was time to enter the activation key.

Drum roll, please! … Entering the key, I chose not to activate on connection to the network, and clicked Next. It accepted it, meaning that the key is a valid key and was good for the 64-bit Windows 7 Professional – fantastic. I choose not to active, because I prefer the customer to activate manually when they connect on their own internet connection. I don’t want too many Windows activations coming from my internet – call me paranoid, if you like.

Anyway, Windows was installed, and came up. I logged in and went to Device Manager, there were a few devices without drivers.

Ethernet controller, PCI Serial Port and PCI Simple Communications Controller. I noted down the hardware ID’s for each of these, as I use the ID to find the right drivers. The Ethernet controller was easy – just go to Dell’s website and enter the Dell Service Tag number, and you get to the support page for this machine. Choose Drivers & downloads, then the operating system, and go to Network. I chose the Intel 825xx Gigabit Platform LAN Network Device Driver. While I was there, I downloaded a few others including the video driver and importantly the latest BIOS update, which was A16 – the current BIOS was A04, quite old it seems.

The downloaded files were put onto a USB disk, and then transferred to the Dell. The BIOS update was run first, it wants to reboot, then do the BIOS upgrade and says that it could take 10 minutes – afterwards I came back to see a blank screen. I left it a bit longer, then it was still the same, so did the BIOS firmware update work or not. I then realized that I had left the USB disk plugged in – that one is not bootable, maybe that was it, so removed it and pressed Ctrl-Alt-Del, then screen blinked then Windows was booting. Feel free to breathe a sigh of relief – I did.

BIOS firmware updates these days should be fairly straight forward, but they did not use to be. Occasionally you end up with a brick, i.e. motherboard that will not boot any more, so manufacturers started coming up with ideas and technology to get around this, by having another boot environment in case of BIOS failure. I don’t think this particular Dell has this.

The PCI Serial Port and PCI Simple Communications Controller drivers was a bit harder to find. There was lots of queries on the internet for these drivers, that somehow could not be found. The hardware ID’s match the vendor 8086 to Intel. Then the Device ID 3B67 and 3B64 on google – told me that I need to find the Intel Active Management Technology driver and the Intel Management Engine driver to resolve these two devices. Fortunately, both searches on Intel actually link to the same download file.

https://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=18531&lang=eng
https://downloadcenter.intel.com/Detail_Desc.aspx?lang=eng&DwnldID=18532

After installation, no more unknown devices in Device Manager. This Dell OptiPlex 980 desktop has been reinstalled.

[NOTE] BIOS updates – you should keep up to date with the latest BIOS updates since this can fix performance and other problems. If a BIOS update goes wrong, i.e. worst case is that the machine no longer boots – there are ways to get around this. Most BIOS roms are stored in Serial EEProm on the motherboard – generally in a SOP8 package and it is possible to obtain in-circuit programmers for this. Other manufacturers have resorted to BIOS recovery mode, or to choose a failsafe BIOS that then allows the BIOS firmware upgrade to be retried.

[NOTE] On the use of USB disks. It is best not to have USB disks bootable in case of virus infection and spreading of viruses. However, a virus that affects the boot sector of a USB disk, will still be a hazard if the USB disk is bootable. I generally don’t make them bootable unless it is for the use of updating firmware or running specific utilities. I keep them separate to my other disks that are used for transferring files.