Dreamcast PSU Fuse problem

Hiya

I seem to have an issue with my newly bought PAL Dreamcast. Whenever I connect it to the power supply and try to start it up, the PSU fuse seems to blow. I have tried different mains power supplies of varying amperage, such as a 3A, 5A and a 13A one, 250V, and the fuse still gets blown. I've gone through more than 4 fuses like this, as I was under the assumption the problem was with my mains plug and not the Dreamcast's PSU. I'd appreciate it if anyone could shed some light on this issue for me, as I am not that knowledgeable with regards to this, and I don't really want to replace the PSU completely if the fix is a relatively simple one. Thank you!

 

It sounds like you have a bad power cable - there is a 1.6A internal fuse in the power supply which is connected directly to the power input socket, and I can't think of any internal failure condition that would result in the fuse in the plug blowing and not the one inside the PSU. Check to make sure there are no metallic foreign objects in the DC power connector and replace the power cord.

 

Thanks for the reply, and apologies if my wording wasn't really clear, its actually the fuse in the dreamcast that is blowing up, not the fuse in the power cables I have used. I used 3 different power cables with different amperages, and the fuse's still blew up inside the dreamcast. All 3 power cables work fine on different devices, so they weren't damaged after use. Thanks for your help!

 

OK, if it's that fuse, there are a whole bunch of things that can cause it to blow. Have you got a meter? Try checking for a short across the AC input terminals of the rectifier (D001).

 

Yes I do, although I'm not sure what the AC input terminals are. I used a continuity test and tested each of the 4 legs with each other and there is a beep for all of them. I also checked the 2 legs that are next to the transformer like thing with the other 2 pins which are coming from the transformer like thing, there is a beep for all of them once again. I am attaching a photo to try and explain the pins I am talking about. Is this the right way to check it? Thank you very much for the code number as well!

 

OK, the thing that looks like a little transformer is a common-mode choke, it's part of the filtering circuit used to keep interference out of the power supply. Those two traces you have drawn the red lines around are the AC input terminals of the rectifier. From what you're saying, it sounds like it's blown, but you really need to remove it from the circuit to be 100% sure. Another thing you can test is to remove the rectifier, replace the fuse and then see if it still blows - if not, then the fault must be at that point or later.

 

Oh I see, so should I basically desolder the item circled in red, (I assume this is called the rectifier?), and then try and fire up the Dreamcast, or the other things circled in blue and green as well? Thank you very much for your help, and sorry if I come across as asking silly questions, I really don't know much about the Dreamcast. Thanks!

EDIT: Is this what I should purchase to replace the items circled in red and green? http://www.ebay.co.uk/itm/5-X-CAPAC...757892?hash=item3f265fe304:g:ZyoAAOxy8HlSa8AD

 

OK, the parts you have circled are the line filter components - they are probably OK. The rectifier is that small black 4-pin device just to the right of your marking.

The part you need is something like this:

http://www.mouser.hk/ProductDetail/...=sGAEpiMZZMtQ8nqTKtFS/LDhWhDI65nsCG8HI6Wu9fo=

 

Oh right apologies for that, oh I see alright thank you for pointing that out. Thank you for the link, but unfortunately P&P is 30x the cost of the item itself. I managed to find this on eBay, and the specifications do seem to match up to the one you linked me to, do you think this one is fine? http://www.ebay.co.uk/itm/FAIRCHILD...382994?hash=item3f2b4ca552:g:mjYAAMXQAx9RT0fN

 

Hiya, I've managed to desolder the rectifier, and then I tried to start up the Dreamcast, and it wouldn't light up. So does this mean the problem is with the rectifier itself then? I've attached a photo of the board with the rectifier desoldered, just in case. Thanks a lot for all your help!

 

OK, now you have the rectifier, check across the AC input terminals (they should be marked with ~ symbols) - I suspect you will find they are shorted out. If they are, then the rectifier is definitely bad, but it might not be the only part that is - the fact that the fuse didn't blow with it removed shows that the line filter components are OK. it's worth also checking that switching transistor / FET that's screwed to the heatsink just left of the rectifier location for shorts - check it in-circuit first, and if it looks like it's shorted then remove it and test in out of circuit to be sure.

Note that you should check the transistor even if the rectifier is confirmed bad - it's quite common for one part to fail and damage another, and in this case it's quite possible that the transistor was the original failure part and the rectifier was subsequently damaged by the fault current.

 

I couldn't seem to find the ~ symbol, but I did check the + and - terminals, and although there is a change in the values displayed on my multimeter, (such as a jumping around in the the values, and finally stabilising around 450) there is no beep when performing the continuity test. When you say the FET, is it the item circled in the photo? Because if it is, I have tested all 3 legs with each other, and I am getting a beep every time regardless of which leg I test with another leg. I am unable to find a replacement that seems to match the FET's specifications, on aliexpress or ebay, perhaps it's just me not understanding the specifications properly? Thank you very much for your continuous help mate!

 

Yeah, that;s the part - remove it and take a photo of the numbers on the front, I should be able to ID it

 

I was unable to remove it because the tip of my soldering iron is very large, I've got to get another tip, but I did manage to take some pictures of the front. Incase it is not clear, it says:
Japan
K2129
A symbol in the form of an M 95

Thanks a lot for all your help!

 

OK, that's going to be a 2SK2129 - it seems to be an obsolete part, but there are people selling NOS ones on ebay.

Based on the datasheet, there is nothing special about it, but it's probably best to use the original part.

http://pdf.datasheetcatalog.com/datasheet/panasonic/2SK2129.pdf

 

Thank you for the part number as well as the data sheet, I had a look on eBay, but based on the photos, none of them seemed to match my part, although they were the same model number. After having a look at aliexpress, I had the same problem, but the parts do seem to be much cheaper. I found these, do you think either of them are fine to order?
https://www.aliexpress.com/item/IC-..._3&btsid=f1a55927-ca5b-4fa8-825b-5958e9fc6ea7

https://www.aliexpress.com/item/10p..._3&btsid=f1a55927-ca5b-4fa8-825b-5958e9fc6ea7

Also, for the rectifier, I wasn't able to find any sellers on aliexpress selling a Fairchild Semiconductor DF08M, but there were lots of DF08M's on offer made by different firms. On eBay I found this person selling it, http://www.ebay.co.uk/itm/271309382994 and the specifications do match up with the mouser.hk listing so do you think I'm good getting this then? Thank you very much for all your help, I honestly really appreciate it!

 

Where did u purchase the dreamcast? I may have a spare psu I could spare if your venture proves unsuccessful.

 

Thank you very much for your generosity, I purchased mine in the UK. Thanks for the offer!

 

That 2SK2129 should be the same as your original one (that symbol with the M in the box with the rounded corners is the Matsushita/Panasonic logo), so your original FET is a Panasonic part.

Those rectifiers are generic parts - any supplier will do. I picked the Fairchild one basically at random.

 

Oh I see thank you, so basically it needs the M symbol within the rounded box, the numbers next to it are irrelevant? Like mine says 95, but the ones on aliexpress vary, some say 5N, and others say 933, are these the batch numbers or something? Alright, thats great, I'll order both things off aliexpress, they are much cheaper on it anyways. Thanks once again!