TideLog Archive for the “Consumer Electronic Repair” Category

Electric showers are great, but they do go wrong occasionally. At Kitamura we repair all types of showers. A lot of people seem to confuse “power showers” with “electric showers”. They aren’t the same. An electric shower simply heats the water, the water goes through the shower under simple water pressure itself. That is where power showers differ. They still heat the water, but they also have a motor assisted water pump, which acts like the turbocharger in an engine, where a little amount of pressure is converted into massive pressure by an impeller.

We recently got called out to a faulty Mira Essentials electric shower. These were made in 2000, and this one was suffering from random pressure drops, and weak output. Here’s a shot of under its cover, I’ve labelled its parts which I’ll explain below:

Electric-Shower-Components

A. Water input w/filter

The cold water input, with filter. This is a gauze filter that filters any silt in the water. If not filtered out it could collect in the water heater, and cause failure, or blockage in other parts of the shower system.

B. Water impeller.

This is not electrically assisted as in a power shower, but it helps to keep the shower running if there is momentary pressure drop due to something else being used in the water system like a tap.

C. Power and Temperature knob with flow solenoid

This is the ON/LOW/MED/HIGH selector, which works in tandem with two microswitches, and two heating elements. When the shower is switched on, the electric flow solenoid opens, allowing water flow. In the LOW position the water heater is fully switched off, and the water is cold as all microswitches are open. In the MED position, one microswitch is closed, so one of the elements is active, and in HIGH both switches are closed, making the heater operate at full wattage, in this case 4.2kw.

D. HIGH microswitch

This is the microswitch that operates the second element by turning the temp knob to HIGH as above.

E. Temperature knob.

This works by varying the amount of water that gets through to the output. By reducing the speed of water flowing through the heater, it makes the water hotter, and increasing it makes it colder. If the Mode selector is HIGH and the Temp knob turned all the way to HOT, the heater would be shut off by the TCO (Thermal CutOut) on the heater as the water temperature is too high, which will cause scalding to the person using it, and also damage to the heater.

F. Neon indicator PCB

This board contains the neon indicators for Power, Overheat, and Low Pressure. It also contains resistors to prevent premature wear of the neon bulbs, they are run from 240v and don’t last long, especially the POWER indicator, as that is on as long as the mains is on.

G. Mains input terminal block

Self explanatory, this is where the mains is wired in to the shower. In this case the shower had its own switch and fuse in the consumer unit, so we didn’t have to turn the electricity off to the customer’s entire house while we worked!

H. Water heater with TCO (Thermal Cut Out)

Here’s where the water is heated before going to the shower head. The two elements are individually controlled by the microswitches previously mentioned in C, controlled by the MODE knob. The heater contains a thermal cutout so that the elements are turned off if the water gets too hot. Once the water reaches a certain colder temperature, the thermal cutout switch turns the elements back on.

The thermal cutout is normally only activated if the temperature knob is on HIGH, and the TEMP knob set to its hottest, which is minimal water flow, as mentioned in E.

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A customer recently booked her Samsung TV in for repair with us, saying it was clicking, and not actually coming on. I’ve had this problem with an old Toshiba plasma of Kana’s over at White Tiger Martial Arts Academy, it was clicking badly, but actually worked, with visible distortion on dark scenes. In that case though, it turned out to be the plasma panel itself stressing the supply, as we couldn’t source a panel at less cost than the TV it had to be written off.

LCD’s though are much easier to source, and will never actually stress a high voltage supply as they themselves only run at 5v DC on their LVDS bus, so once we’d picked the customer’s TV up from her house, we took off its cover, and took a look. It turned out to be one of our most common problems: Bulging capacitors! Except these were high quality Korean Sanhwa ones. Once you get the cover off (just 12 screws, no plastic clips unlike Vestels!) you’ll see the PSU on the chassis. It uses a massive flyback transformer and opto-isolator for SMPS feedback, to power the backlights. If you thought flyback transformers died with CRT’s, you were wrong!

Samsung LA40R81BD-PSU-removal

Follow this procedure to remove the supply:

CAUTION: WAIT at least 30 minutes if the TV has been plugged in. If you are experienced in electronics you can discharge the main filter capacitor using a resistor, if not, leave it unplugged for a while before continuing, and have a brew, thinking about how you’ll proceed, and make notes. I find cuppa-plan time to be very productive, and it keeps me safe, even as a professional. There are high voltages present that can KILL!

1. Remove all connectors I’ve coloured GREEN. They have tabs on them which you must push as you pull the connector. DO NOT pull them out by the wires, you’ll rip the socket off the board and damage the socket pins, making this cheap repair much more expensive.

2. Unscrew and remove all screws I’ve coloured RED, and put them somewhere safe. Remove the board by lifting it by its EDGES, not by a transformer or capacitor, or any other component. Place the board on a suitable workspace, with plenty of room, and an antistatic mat. SMPS supplies contain surface mount components and controllers which are easily damaged. Simply walking on a carpet generates 70,000V which we can only feel as a slight shock as there’s hardly any amps, but that is more than enough to wipe semiconductors out!

Samsung LA40R81BD PSU capacitors

3. You’ll notice near CN801 there’s a bunch of capacitors, and some of them will likely be bulged, or have actually vented. If any vents have burst, you must clean the electrolyte off as soon as possible, as it’s corrosive to the board and other components. I generally replace all output caps if any have become damaged, as they will have been stressed. On my board there were 2ea 2200uf capacitors that were bulging. Remove the old capacitors ensuring you don’t overheat or damage the copper pads/tracks on the circuit board.

CAUTION: Take care to ensure you install the new capacitors correctly. They are polarity sensitive. The board and capacitors will be clearly marked which way they should be inserted. Shorted or polarity-reversed capaitors can EXPLODE and/or damage other parts of the circuit.

You should check and if necessary replace any adjacent capacitors that are rated 10V as these seem to be the ones more likely to fail. In my case I also replaced the 1000uF capacitor. Capacitors, contrary to misconception do not have to look visibly damaged to be faulty, they can be internally dried out.

NOTE: If replacing the capacitors does not resolve your symptoms you may need to replace the EEPROM chip on the main board as it can be corrupted or damaged by the power cycling. This will need to be done by a professional as the software contained in it can be TV specific.

 

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I’ve had this problem a few times on my laptop. It occurs mostly when the power suddenly goes off and it switches to battery. You lose all capacity monitoring, and can’t tell how much is left. The system tray icon changes to this:

no battery detected

Microsoft’s forums are hilarious. Their “Most Valuable Professionals” give the funniest canned cut ‘n’ paste responses, from, “Your power driver is corrupt” to your “Windows needs reinstalling!”. I know exactly what causes it, and it ain’t anything to do with “power drivers” or corrupt Windows. It’s the little monitoring chip in the battery. Like a lot of integrated electronics, it sometimes gets confused. Sudden switchovers from mains to battery tend to cause it, especially if there’s any surges from the battery as it kicks in.

The age old advice of “Reboot!” is the wise advice. If that doesn’t cure it, turn your machine off, remove the mains and battery, and hold your power button down to discharge the circuitry in your device (apart from the RTC circuit, but this doesn’t matter), that should cure it. Removing the battery opens the circuit to the sensing system in the battery, and resets it.

Simples. I hate MVP’s, they go on a 5 day course and think that gives them a Professional title? I’ve done MVP courses, but have the skills and years of software and electrical experience to further and back them up

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I recently had a TideLog reader, Steve, contact me about his Menvier TS800 control panel, saying the panel was fine, but the charge voltage was intermittent, even with a new battery. A few days afterwards he dropped it off to me, lo and behold, just like the Optima, a worn resistor, under the keypad. Here’s a picture of what it should look like, and where it is located:

Menvier-TS800-resistors-locationThe one I’ve highlighted in green, labelled R52, supplies the +ve 13.6v feed to the battery, via D14 to the bottom left of it, which also seems to supply the telephone module terminal block with +ve voltage too. R83, which is the green resistor highlighted in blue, supplies the AUX 12v for PIR’s and such, and 12.6v to the bell.

Check both resistors, and all diodes for continuity and correct resistance, use my band code chart, in the Optima article, by clicking HERE. R52 on Steve’s board wasn’t badly burnt, but the resistor ceramic coating, along with the colour bands, had come off, there was slight burn evidence at the solder joints, and the voltage was stable until the board was under load, once the resistor warms up it breaks down when loaded with a flat battery on the charge rail.

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When a hard disk is manufactured, there are areas on the platter that have bad sectors. Considering that on a 2 TB hard disk there are 4 billion sectors, then a few bad sectors is only a tiny proportion of the total number of sectors on the drive. During the test phases of a hard disk, the platters are scanned at the factory and the bad sectors are mapped out – these are generally called ‘Primary Defects’. The primary defects are stored in tables in the firmware zone, or in some cases the ROM of a hard disk. When you buy a brand new hard disk, you will most likely be completely unaware of these bad sectors and the numbers because they are ‘mapped out’ using ‘translator‘ algorithms.

Modern hard disks use Logical Block Addressing or LBA, this describes the sector numbering system on the hard disk, and goes in sequence
0,1,2,3,4,5,…..n-1,n (where n is the last sector on the drive.

Spare sector pools

All modern hard disk drives have a spare sector pool. This is used when bad sectors develop during the normal life of the hard disk and any newly found bad sectors are ‘replaced’ with good ones from the spare sector pool. This process is invisible to the user and they will probably never know that anything has changed.

How Bad Sector Mapping Works:

There are at least two methods of bad sector re-mapping (or translation) these are P-List and G-List.

  • P-list are defects found during manufacture and are also know as Primary Defects
  • G-List are defects that develop in normal use of the drive and are known as Grown Defects

There are other defect lists found in modern drives but the principles are similar. For example, you may find a T-List or a Track defect list, or an S-List or System area defect list.

P-List Remapping
Lets get into how these defect lists actually work, so let’s say we have a small hard disk with 100 sectors and a 10 sector spares pool.

When bad sectors are found at the factory, shift-points are entered into the P-List, if we take the following LBA sequence 0,1,2,3,4,5,6,7,8,9,10 …99, 100 Lets say that Sectors 3, 6 and 9 are found to be bad. When the first bad sector is found, the first part of the re-mapping process will look like this

0,1,2,B,4,5,6,7,8,9,10 ..

What happens here is the bad sector at position 3 is recorded in the P-List. The new map now looks like this;

0,1,2,P,3,4,5,6,7,8,9,10 ..  You can see now that 3 is where 4 was.

The next bad sector at LBA 6 is now found

0,1,2,P,3,4,5,B,7 and is again mapped out giving 0,1,2,P,3,4,5,P,6,7

When the whole sequence is complete, our final map looks like this.

0,1,2,P,3,4,5,P,6,7,8,P,9,10

Because these sectors are mapped out, the user will never be aware that they exist. If you want to look at sector 6, the drive will translate that to physical sector 8. It takes the 6 and adds the shift points to it, +1 for the bad sector at LBA3 and +1 for the bad sector at LBA 6. When the testing gets to the end of the drive, in order that it is of the correct size of 100 sectors, it allocates the sectors from the spare sector pool completely concealing the fact that there are bad sectors on the media. To all intents and purposes the drive looks just like the original as 1,2,3,4,5,6,7,8,9,10. However, our spare pool has reduced in size and there are now 7 sectors remaining in the spares pool.

After using the drive for a while some bad sectors develop the drive takes care of these using a grown defect list.

G-List Remapping
The grown defect list or G-List is a table containing the location of bad sector defects found during normal operation of the hard disk drive. When a bad sector occurs during normal use of the drive, something a similar process to P-List generation occurs – resulting with the bad sectors being mapped out. The process for G-List mapping out is slightly different. Lets say our hard disk develops a bad sector at the current LBA 6. What happens in this case is first the bad sector is mapped out. Giving; 0,1,2,3,4,5,G,7,8,9,10 .. A sector from the spare pool is allocated in the bad sectors place. We used 3 of these sectors in factory testing, so the next available bad sector is 104 this now becomes mapped to LBA 6 so our sequence would look like this; 0,1,2,3,4,5,104,7,8,9,10

Again, this process is completely invisible to the user and will still look like the original sequence of 0,1,2,3,4,5,6,7,8,9,10

You might ask, ‘why don’t the new defects get added to the P-List?‘ the answer is that if you add a grown defect to the P-List it has the effect of shifting the data up the drive for each sector from the point where the new bad sector is found. If you look again at the methodology behind the P-List it will help you understand this.

Where a G-List entry can help to revive hard disk, if there was data stored in the original sector attempts then usually it is lost. This may appear to the user as a file that not longer opens, or a a program that doesn’t run anymore or some other errant behaviour. This will not become apparent until the next time the file is attempted to be opened. It may also be that it is such a long time since it was opened that a backup plan means there are no backups of the working version. So bear this in mind when developing you backup plan.

Defect Mapping in a live system
When a hard disk is powered up, the p-list and g-list are usually loaded into RAM on the controller card. As requests for data come through, the location where the data is required from is passed to the translator, which makes the calculations necessary so as to determine which sectors to actually read in order to get to the actual data requested. In our example above, if we wanted the data from LBA 6 the translator would first run through the p-list and add 2 sectors to the count for the two bad sectors found at the factory, it then checks this value in the G-list and finds it has been re-allocated to sector 104. It then reads sector 104 and presents you with the data.

All the magic that goes unnoticed by normal people 🙂

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