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  Difficultly of Mephisto Exclusive/Munchen repairs?
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   Author  Topic: Difficultly of Mephisto Exclusive/Munchen repairs?  (Read 1110 times)
tony
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Re:Difficultly of Mephisto Exclusive/Munchen repairs?
« on: February 14, 2011, 08:14AM »
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Kostea, that's good info. the hamlin reeds are available as I bought  some about 2 months ago. the SDR-7 is a perfect replacement. they are also really cheap if bought in quantities of 10 or more. regards, tony
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Kostea
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Re:Difficultly of Mephisto Exclusive/Munchen repairs?
« Reply #1 on: February 13, 2011, 03:17PM »
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TerryG has already answered your question.

The best thing is to take apart your board and measure the length of the reed switch's green glass capsule.
If it is between 12-14 mm long, then you can use these parts:

1. Meder Electronic

part #  KSK-1A66-1015


2. Hamlin Electronics Ltd

part #  FLEX-14 10-15
part #  MDSR-7 10-20

If you put off the repair for 6 months, and later on you can't find them anymore because the manufacturers came up with new products and part numbers, then buy reed switches that have these features:

- magnetic reed switch
- glass body
- SPST (single pole single throw; this means it is only one contact inside the glass capsule)
- NO ('normally open' contact; also known as 'Form A')
- AT value between 10-20
- switching current 500mA
- switching voltage 100V
- axial (2 leads/terminals)

Under normal functioning, the switching current and voltage are far lower than I listed them above, but buy the 500mA and 100V at a minimum, it doesn't really cost extra.

The diodes are 'switching diodes' types such as: 1N4148, 1N4448, 1N914 or equivalents.

The reed switches are at least 10 times more likely to fail than the diodes.

I would first check for bad solder joints on the reed switches and diodes. Probably a good idea to remake the solder joints before you replace anything.
However some chess computers are a little difficult to get to the reed switches, and in that situation I just prefer to replace the reed switch anyway, because they are not expensive. The less you open these boards the better.

Regards,
Kostea
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TerryG
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Re:Difficultly of Mephisto Exclusive/Munchen repairs?
« Reply #2 on: February 9, 2011, 06:56AM »
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Hi,
    You probably have a faulty diode/LED or reed, there are several posts on this forum covering changing these components. I have a Mephisto Exclusive and Academy, both have required attention to the 'squares' on occasion.
        If you login and put in 'reed' in the search option a lot of information comes up, much of it will be irrelavant but some Mephisto and Conchess etc will help. The diodes are usually 1N914/1N4148 the LED usually about 3mm types and most reeds require approx 15mm types available from some good electonic components stores (in the UK there is e.g.Maplin) os maybe Ebay, just search for 'magnetic reed'. For Munchen boards I expect a larger reed can be used- I have used 25mm for an Exclusive although they are rather too big - having to bend back the wire, you have to be careful so not to break the glass tube.
          To access the Exclusive (Munchen too ??) turn over the board on a protective surface unscrew the feet then unscrew the screws. If I recall you have to take a few more screws off so that the whole can be slid out. Next the paxolin PCB has to be un stapled then the square identified. See below for my post on the Academy for further tips: -  (good luck)


[i]Bobosse,
                    I agree with Mychess that the diode is most likely 1N914 / or 1N4148 common switching diode used on many applications to block reverse current to another part of the circuit.
If you have a multimeter (digital, preferably) measure across one of the other diodes (they are usually oriented the same way, like on your photograph one end has a black band). Then measure your suspected diode, in one direction you will get about 600 - 900 ohms, when you reverse the meter leads there should be no measurement, not even on the highest scale(over Megohm).
If you suspect a faulty diode then again measuring across a replacement and soldering it in place so that it is in the same orientation again. The replacement may not have the same colour bands but virtually any high speed switching diode will do the job.
Note it will not be a zener diode as they are used for power regulation circuits and they are connected in a reverse direction, as they only conduct when the voltage approaches its breakdown value.
It's a fairly simple job to replace diode or indeed LED or reed (usualy far easier than getting to it!!), but if you are of a 'certain age' like me seeing up close can be a bit tricky without a magnifying glass. It's also a good idea to make sure if any other components need changing like LED's, as occasionally they can get a bit dull.
                        Terry

see my post August 21 2009;

  ....... I recently changed an LED on my academy and thought I'd share my experience. I have taken several photographs of the procedure but cannot see how I can upload them, can anyone advise?

      First remove all (9) screws from the base. Then the 2 screws from the module cover. Taking care not to present any static charge to the components, carefully fold back the main computer pcb (away from you). It is handy to do this on a workbench or table with perhaps a newspaper to protect the surfaces. Remove the screws from the playing surface where the reeds etc are (I've forgotten how many there are - sorry) to remove from the wooden case.

Most of this procedure has been covered befor, however here it is again After identifying the the faulty square, place a chess peice above and listen to hear if the reed operates. Connecting a test meter across the reed will determine if the component is faulty - a high resistance then it is faulty but if a short circuit, then the reed is ok and the faulty component must be the LED or diode. In my case I proved the LED faulty. Unsolder the appropriate component taking care not to splash solder over the pcb. Insert component making sure LED or diode is correct orientation, test first if unsure. If changing a reed be very careful not to crack the glass case.

When all done reassemble, the module cover is rather tricky to replace as the screws are very short (a few swear words could be heard coming from my workshop when I did this). Hopefully all will be well and the Chess computer works. In my case it had a new fault!When I turned on my machine I got an 'Error' - if I reset the machine it would work ok, but after being switched off for about 10 minutes the error would reappear. (turning off then back on soon after, the machine was fine).

[b]I got thinking that the memory backup battery must be faulty. I took the thing all apart (again!) then tested the CR2032 battery, which was only 0.4volts. Mephisto computer batteries are welded to the holder so the lot has to be removed and a new holder obtained (and new CR2032 battery). In the UK I obtained part number LOAC1 from Maplin supplies. I drilled another hole to take the new holder - making sure contact was ok to the + and - pcb tracks. The holder had small feet which I snipped off as the battery now sits higher on the pcb. Also to prevent any touching to the playing board pcb I stuck a few layers of insulating tape on the pcb. With it all reassembled the computer now functions perfectly and the game can be saved for presumably until the battery runs out.

            Terry
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TerryG
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Difficultly of Mephisto Exclusive/Munchen repairs?
« Reply #3 on: February 8, 2011, 10:58PM »
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Periodically I come across these boards with stuck squares.  Assuming the reed switch is jammed closed or failed, what's the repair method?  Is there an equivalent size part available as a quick fix, just solder in the replacement, or is it an unavailable part causing us to sacrifice other boards to fix them?
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