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Central Unit 6021 doesn't work = after 4 attempts it is fixed
Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Hi, bought this central station about 12 month ago second hand and never used it since than, so I never tried it if it actually works. yesterday I've connected it and the digital display works, on and off button works but no loco responds to any number under any settings (4 digit). is it just the memory whereas you have to re-charge it from time to time or is the central unit as well, I have done this overnight but nothing has changed. and there is power to the track so it must be within the central unit any help would be appreciated regards., John Edited by user 11 July 2016 07:19:05(UTC)
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Usually with the 6021 it is the output transistors that have failed and need replacing. Replacements are readily available and I'm sure you could do this yourself. There are previous threads in the forum on how to do it and the types of transistors used (I know they are Darlington transistors, but the type escapes me at the moment).
It sounds like all of the other buttons work OK on your 6021, so given the symptoms I think it is the transistors that have failed.
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 2 users liked this useful post by Bigdaddynz
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Originally Posted by: Bigdaddynz  Usually with the 6021 it is the output transistors that have failed and need replacing. Replacements are readily available and I'm sure you could do this yourself. There are previous threads in the forum on how to do it and the types of transistors used (I know they are Darlington transistors, but the type escapes me at the moment).
It sounds like all of the other buttons work OK on your 6021, so given the symptoms I think it is the transistors that have failed. Dave any hints what I should search for ? central unit 6021 ? John |
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Transistors are standard BDW93C/94C Darlingtons. (Note: insulation from the heat sink is required - which means you need the insulating washers that go with the transistors, plus some heatsink compound). You should replace both transistors in a pair. Here's a post from Peter Clapcott regarding symptoms of blown 6021 transistors - https://www.marklin-user...l-with-6021-control-unitOriginally Posted by: clapcott  Tex,
I would suggest that a short has (had) developed between the yellow and red. This results in stressing the driver transistors of the 6021.
2 situations usually occur - 1 A "good" short - will blow the transistors - 2 A "poor" short will make them sluggish
Your description is typical of (2) - a poor short with the the transistors delivery power but not crisply enough for the decoder to understand - A loc will therefor assumes "analogue mode" and will take off at 2/3 speed.
occasionally different address patterns may make the signal recognisable but this is borderline.
replace BOTH driver transistors
BEFORE you connect it (or any other controller) to the layout thoroughly check for yellow<> red shorts,
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 1 user liked this useful post by Bigdaddynz
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Originally Posted by: Bigdaddynz  thanks Dave, I've opened the unit but couldn't find anything visual hence I have put it back together again but AI will buy these transistors today and see what happens. de soldering the transistors shouldn't be a problem as I have a soldering iron which has a type of grab plier points. appreciate your quick help  regards., John |
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Joined: 28/11/2007(UTC) Posts: 8,226 Location: Montreal, QC
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Originally Posted by: river6109  Hi, bought this central station about 12 month ago second hand and never used it since than, so I never tried it if it actually works. yesterday I've connected it and the digital display works, on and off button works but no loco responds to any number under any settings (4 digit). is it just the memory whereas you have to re-charge it from time to time or is the central unit as well, I have done this overnight but nothing has changed. and there is power to the track so it must be within the central unit any help would be appreciated
regards.,
John The 6021 works with 2 digit (00-81) for addresses. Not quite sure what you mean by 4 digit. The dip switches on the rear should be set all off except #2 on. Make sure that both the L and F lights are on. If only one is on, the unit might not communicate with locomotives. I have one 6021 where the buttons no longer seem to fully contact the PCB board. It is possible that the plastic liner under the housing has slipped out of position. Before you go changing any components, double check with digital switch track or other digital solenoid function to see if the function commands work Good luck Mike C
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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the parts mentioned above BDW 93 CFP and BDW 94CFP are not the same on my unit BDX 34C, BDX 33C, does it matter which go in ?
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Joined: 15/09/2014(UTC) Posts: 18 Location: Athens, Greece
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John have you checked the output with an AC voltmeter? If final transistors have failed there should be not any output on the meter. Also the 4 dip switches are all supposed to be off for HO scale...
Regards Manos SV1IW
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Originally Posted by: manos.g.darkadakis  If final transistors have failed there should be not any output on the meter. Not necessarily.......... Originally Posted by: clapcott  2 situations usually occur - 1 A "good" short - will blow the transistors - 2 A "poor" short will make them sluggish
See Peter's quote that I reference in post #4 above.
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Joined: 28/11/2007(UTC) Posts: 8,226 Location: Montreal, QC
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For operation with modern decoders, the dip switch #2 should be moved to on. If all dip switches are off, some decoders will not understand the commands. Please consult the instruction manual for more details.
Regards
Mike C
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Hi all, I'm in the process of ordering the 3 transistors, one company asked A$ 12.95 for postage and this is a no no, I will look again at the aliexprss website although you buy in quantities of 10 you are still buying them cheaper as buying them from any ebay sellers and most the time its postage free. I'm not in a hurry for them but will let you know when I've installed them, have removed the old ones and one BDW m93C looks a bit suspicious.
there is DC voltage on the track and yes if you look at the instruction booklet it show clearly which dip switch should be on or off.
John |
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 1 user liked this useful post by river6109
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Joined: 15/09/2014(UTC) Posts: 18 Location: Athens, Greece
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John voltage may be present on the output of the controller but perhaps not enough current (Amps). So the best way to check this out before getting to replacement procedure is through a load and a voltmeter/Ammeter. Voltage will drop dramatically even with a small load if the transistors are bad. Any cheap Chinese multi meter will do. Regards Manos SV1IW Edited by user 04 July 2016 00:34:19(UTC)
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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since I've got inside the 6021 and took it apart I found the heat sink screw had been used before and also some of the electronic components seem to have been re soldered or replaced before hand. John     Edited by user 03 July 2016 15:31:22(UTC)
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Joined: 23/07/2014(UTC) Posts: 8,468 Location: ENGLAND, Didcot
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Originally Posted by: river6109  since I've got inside the 6021 and took it apart I found the heating element screw had been used before and also some of the electronic components seem to have been re soldered or replaced before hand. John
Ugh !!! I would suggest you clean that PCB with some alcohol and an old toothbrush to get rid of all that white residue. Medicinal alcohol will do as bought from a chemist, such as ladies use for cleaning earrings for pierced ears will work fine. This will get rid of most of the white residue, which I suspect is from a previous attempt at cleaning the rosin off. Called Isopropyl Alcohol, which is available from most Pharmacies /BDNZ Gently scrubbing with an old toothbrush will help to move the residue. When finished if there is still some residue then try with some warm water containing a tiny drop of dish wash detergent, and rinse well afterwards. Your close up of the transistor is out of focus (you already knew that  ). If you have a jewellers loupe tape it over the lens on your phone camera, and you can get real close and be in focus. You will need to be able to get quite a bit of light onto the subject, but as a system it works well. I have used this in the past when looking at defects in PCB tracks. One point about soldering the PCB, use a low power soldering with a very fine tip, and don't keep it on the joint too long. I had occasion to go over the joints in someones 6050 booster, and the tracks were very fine and it was difficult to stop them peeling off the surface. Not sure what you mean by heating element screw - is this a screw into the heat sink, the big lump of finned metal? Edited by moderator 04 July 2016 03:25:12(UTC)
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 1 user liked this useful post by kiwiAlan
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Joined: 12/07/2011(UTC) Posts: 1,068 Location: In a building site in Yeppoon
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A bit hard to tell from the photo's but at a glance it looks like the worst case of "Whiskers" I have ever seen. Well at least for area effected. Regardless John I'd take Alan's advice and recommend sealing the board with lacquer when repairs are finished. |
Sad when its cheaper to buy a new 29640 starter set from Germany than a CS2 on its own in Oz, welcome to the joys of Marklin down under . |
 1 user liked this useful post by Shamu
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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to all: thanks for the helpful advice, will implement recommendations
John |
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Joined: 23/07/2014(UTC) Posts: 8,468 Location: ENGLAND, Didcot
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Originally Posted by: Shamu  A bit hard to tell from the photo's but at a glance it looks like the worst case of "Whiskers" I have ever seen. Well at least for area effected. Regardless John I'd take Alan's advice and recommend sealing the board with lacquer when repairs are finished. I'm not sure if it actually has whiskers, or if it is just the gunge left after an attempt at cleaning the rosin off. Rosin will leave a white deposit that looks like that if cleaned with isopropyl alcohol without brushing or properly washing off afterward, which is what I suspect has happened here.
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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here is a picture of one of the transistors which is not responding on the multimeter from the middle to the right (BDX33C) whereas the other 2 do respond (BDX34C)  |
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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I wonder if those transistors have been changed before, given they are a different type to what is (known to be) normally installed in the 6021.
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Originally Posted by: Bigdaddynz  I wonder if those transistors have been changed before, given they are a different type to what is (known to be) normally installed in the 6021. Dave, very interesting, is there any proof with previous 6021's ? as I have never looked into this although I've opened one before but I can't remember whether it was just pure curiosity ? maybe the person who sold it to me may can shine some light onto it ? I doubt it thou as I can't remember who sold it to me. John |
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Hi, thanks again for the supply of transistors (Peter C.), arrived today. 6021 first attempt: fail = DCC mode 6021 second attempt: fail = all 4 levers off 6021 third attempt: fail = number 2 on 6021 forth attempt: SUCCESS = number 2,3,4 on cause: 1, 2 or 3 transistors broken I wonder how many people discard components like this and especially with white goods, some of them stop working after 12 month. we've got a Fischer and Paykel twin dishwasher and most of the plastic components within the electronic circuit boards have more or less disintegrated, we've got a serviceman out and he couldn't or wouldn't fix the dishwasher unless we agree for him to fit new parts, in the end it would have been cheaper to buy a new one but every time he connected the dishwasher another part failed, never again will we buy this brand, these days it is a common acceptance if your appliance is more than 3 years old throw it away and the experts tell you don't throw your old fridge or freezer out the new ones will never last the same period. John Edited by user 11 July 2016 14:05:35(UTC)
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Originally Posted by: river6109  .......is there any proof with previous 6021's ? The transistor types that I quoted are based on the info Peter C advised based on his repair of 20+ 6021's, plus what other forum members have advised. Originally Posted by: river6109  We've got a Fischer and Paykel twin dishwasher and most of the plastic components within the electronic circuit boards have more or less disintegrated.......never again will we buy this brand A good New Zealand brand, but they're not made in New Zealand any more - Fisher & Paykell are now owned by the Chinese (Haier) and are made in Mexico.
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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 2 users liked this useful post by river6109
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Joined: 30/01/2006(UTC) Posts: 1,893 Location: Keene, NH
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Congrats on getting your 6021 repaired! |
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 1 user liked this useful post by mmervine
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Hi,
unfortunately, the 6021 failed again today, on its own it worked fine, added another controller (80F), worked fine, added another 80F and it failed, so I may have 2 problems, the 3rd controller I've added or the 6021 internal circuit board is faulty somewhere else (which sounds unlikely), maybe some of you could fill me in what the course it is this time, will open the 3nd 80F controller and see if I can find something.
John |
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Joined: 23/07/2014(UTC) Posts: 8,468 Location: ENGLAND, Didcot
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Originally Posted by: river6109  Hi,
unfortunately, the 6021 failed again today, on its own it worked fine, added another controller (80F), worked fine, added another 80F and it failed, so I may have 2 problems, the 3rd controller I've added or the 6021 internal circuit board is faulty somewhere else (which sounds unlikely), maybe some of you could fill me in what the course it is this time, will open the 3nd 80F controller and see if I can find something.
John before opening it, what combinations of the c80f units have you tried? Do all combinations of two controllers work fine and then fitting the third one (whichever one is left over ) cause it to die? If so it sounds to me like the power supply in the 6021 may not be able to supply enough current. I don't know how many c80f/6050/1/memory units/etc it should be able to handle, but I would have thought quite a few. I would suspect that some other transistor in the voltage regulator portion of the 6021 may have got cooked when the original failure and subsequent repair attempts occurred.
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Originally Posted by: kiwiAlan  Originally Posted by: river6109  Hi,
unfortunately, the 6021 failed again today, on its own it worked fine, added another controller (80F), worked fine, added another 80F and it failed, so I may have 2 problems, the 3rd controller I've added or the 6021 internal circuit board is faulty somewhere else (which sounds unlikely), maybe some of you could fill me in what the course it is this time, will open the 3nd 80F controller and see if I can find something.
John before opening it, what combinations of the c80f units have you tried? Do all combinations of two controllers work fine and then fitting the third one (whichever one is left over ) cause it to die? If so it sounds to me like the power supply in the 6021 may not be able to supply enough current. I don't know how many c80f/6050/1/memory units/etc it should be able to handle, but I would have thought quite a few. I would suspect that some other transistor in the voltage regulator portion of the 6021 may have got cooked when the original failure and subsequent repair attempts occurred. maybe but its strange that the 6021 works with one 80f and not 2 , I don't think there is a restriction on how many you can add but I would think 8 or 10 should be plenty. there is another transistor in the 80f and most probably the ones I've replaced are gone again. will know when I test them. John |
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Joined: 17/09/2006(UTC) Posts: 18,771 Location: New Zealand
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Check that one of the 80f's isn't introducing a new short which then shorts the 6021.
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Joined: 22/01/2009(UTC) Posts: 14,875 Location: On 1965 Märklin Boulevard just around from Roco Square
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Originally Posted by: Bigdaddynz  Check that one of the 80f's isn't introducing a new short which then shorts the 6021. Dave, this is what I thought, I've taken it apart (80F) and have noticed one transistor, the strange thing is, the 80f is from my original purchase and I can't remember it being faulty but its been that long I haven't used it, I've opened it years ago just for curiosity but it may have been faulty but I can't remember. the best thing replace all the transistors again and see what happens. John |
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Joined: 23/07/2014(UTC) Posts: 8,468 Location: ENGLAND, Didcot
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Originally Posted by: river6109  Originally Posted by: Bigdaddynz  Check that one of the 80f's isn't introducing a new short which then shorts the 6021. Dave, this is what I thought, I've taken it apart (80F) and have noticed one transistor, the strange thing is, the 80f is from my original purchase and I can't remember it being faulty but its been that long I haven't used it, I've opened it years ago just for curiosity but it may have been faulty but I can't remember. the best thing replace all the transistors again and see what happens. John I would be more suspicious of an electrolytic capacitor going short circuit after drying out over the years. I remember during my apprenticeship having an electrolytic capacitor do something funny that resulted in a lovely woodgrain finish all over the PPI display of a radar set.
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Central Unit 6021 doesn't work = after 4 attempts it is fixed
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