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Andrew96_

Epoch MK2 and MK1 psu repair

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See on ebay a pile of untested / spares boards, put in a offer and it was accepted! in the pile was this epock mk2 psu board that caught my eye! this is a expanded view of the picture on ebay

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Difficult to see but next to the white power transformer connector there should be a 10A fuse, this had 2 wires soldered and chopped off in place of the fuse! (one of the circles in red). there looked to be something different around the end green led! (another of the circles in red). also the transistor Q1 looked like it had got a bit warm (another of the circles in red) and the other power diodes wither side looked like they have been tried to be resoldered/ displaced from there normal position!

 

I should have taken a better picture of it before starting work on it but I forgot!

Edited by Andrew96_

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OK so firstly remove the fuse wires that had been added and clean up the pads ready for another fuse! then run a meter along the diodes and transistors, the big packages! sure enough Q1 transistor was short and all the other 3 big diodes were ok! so the diode soldering all had extra solder on them, so the solder was cleaned, off, components straightened up and re-soldered and Q1 removed! the capacitors were all removed too as the small radial ones had all been replaced but the soldering was not too great and they were quite away from the board, the big blue cap and transformer was removed to ease access to the other components, and the middle white connector removed as the soldering on the pins of that was not up to my standards and I want to re-solder the connections. R26 and R22 were blown with big burn marks in them so they was removed from the board, D2 was dead short too right by the switch mode transformer, and all solder pads and through holes cleaned! 

 

IMG_2678.JPG.a82d5d6afd11d9b051bbb5bea2a8bffc.JPG

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bit closer view of the bits removed from the board and there locations marked in red

 

IMG_2681.JPG.537bb8f44a452dd27edb2460f4e2480c.JPG

R22 is a bit burnt on the board so some work there is needed!

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also above the ic U3 removed as that will most definitely taken a hit with the way the other bits have blown! not worth taking the risk for £1.50 as if it isn't it could all blow again, so replacement it is! picture above it all cleaned up!

 

picture below all the blown bits, you can see the resistors have blown! no fuse in the picture as that was not on the board!

IMG_2682.JPG.9ef5ae0e526efe14fb318d3302775a38.JPG

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next was the bit by the led! this appeared to have had some wire solder to it in the past and the resistor (R17) was very misplaced on the board! so removed cleaned refitted, the dark patch on the board could be iron burn marks! but there are no tracks there etc so not worried about doing anything to that!the solder joint just below the R of r17 looks brown! but it isn't, it is fine, just the way the light has caught the joint, the resistor is fine and still reads 18k despite a bit of the white marking being disappeared with whoever messed with the  board before!

 

IMG_2683.JPG.eb91a07f5ff7e0c6aa9b2c85e728cf5b.JPG

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slightly more closeup of the solder joints on the resistor

IMG_2684.JPG.eea747414e180fbfa332f16eb4df3e8e.JPG

 

next now is to order up the blown parts!!! this is the second board now I have seen blown up in this way so it may become more widespread in the future, the last board I did like this was in 2014

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Little bit more done tonight, because (I think) when the fuse went on the board 2 wires was connected in its place, so I presume either a external fuse was used or perhaps they was just connected together and powered on just one more time!, either way the tracks suffered! one pad of the Q1 transistor was lifted with the heat, and all around the transistor drive limiter resistor (which was burnt to a crisp!) had also burnt the board!

IMG_2685.JPG.8765643b8bac4a1814c5125a86562858.JPG IMG_2686.JPG.b95f0af8c5506f4d4fa9a931b3dbb796.JPG

 

so the Q1 pad has now been stuck down with special epoxy glue that's resistant to heat etc, and R22 burnt board bits have been scraped out and solder resist applied!

So a new Q1 has now been soldered to the board! care has to be taken to avoid any solderless cavities under the transistor, but all went well and the once lifted looks good also! you can also see the board around R22 looks so much better now

 

IMG_2695.JPG.b6416c68a65ac70d09244f6ec27d008b.JPG

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That one looked like got a little warm, I would imagine that R22 was a bit of a pain to resolve?

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Andrew, I bet you were waiting for my next question...:lol:

What heat resistant expoxy did you use and where from?
Previous searches showed specialist stuff to be too expensive especially for the amount of use it would get and would probably go off and be wasted. If it's a mix your own epoxy then that would be much better. 

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Well Bob, you are right! It is special stuff which my mentor at work helped with as they have the special epoxy there! It’s mixed up placed under the track, then a bit of pressure applied to hold it down,  no idea what it was!! But it worked good! It won’t be cheap that’s for sure as it’s to military approval standards for pcb repair and approved for use on aircraft pcb repairs! I just struck lucky!!

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The good flux is nearly £50 a litre and 1lb if solder is £60, all expensive stuff just for soldering! Then the conformal coating is £200 plus for a 5l can!

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10 hours ago, MikeB said:

That one looked like got a little warm, I would imagine that R22 was a bit of a pain to resolve?

well that had one pad lifted, so I was able to get right under it and use a small drill with a scraping attachment to dig out the burnt bits! then cleaned and solder resist applied in the dip that was left, then the pad put back level on the top and dried with UV light, it is not perfect but it is fine for this job as is just a gate current limiter for the mosfet, so it does not (normally) have any great current through it and being just 22 ohms there won't be much if any voltage difference across it either! so it is good enough in this case!

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R22 finished! no burnt board! solder resist is darker than the original on the board so that's why it still looks dark!

IMG_2697.JPG.f28949fc2d083e269e767747524afaaa.JPG

 

The rest of the surface mount components I have now back on the board tonight, 2 resistors, ic, and diode, all looking good!!

IMG_2698.JPG.60805345ffb9dd245a64e6197d8bcec2.JPG

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ok so now the bit I don't like! pcb rivets!

 

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put in place and flattened off!

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and tinned!

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well that went better this time! think I am finally getting the hang of them!

topside view! the left one

 

IMG_2708.JPG.87f99edae704a38f4b7e2ee8203cb557.JPG

wonderful!!

Edited by Andrew96_

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I was quite surprised when you said you didn't like them but you've done a nice job there. I wouldn't be without them as they've saved many a board from the tip!

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The 10A fuse  arrived today so I was now able to complete putting it back together!, before that I did connect the board to my varable  current limited variable power supply and the switchmode bit on the board I have just repaired did oscillate correctly and produce volts on the output pins! so at least I know it is not going to go bang again! its working as much as I can tell before putting it in a machine!

 

this is how the board looks now it is finished! all joints looking like they have never been touched and looking original is the aim!

 

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IMG_2720.jpg.4040e873352206a0faca6296c60a2042.jpg

 

looks good to me!!

 

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power applied from my variable power supply, 2nd from each end led's are not lit as expected as these  are sync led (for which there is no ac applied to the board so no sync waveform present) and 24v which does not normally light on the MK2 psu's until the mpu tells it to turn on for the hopper supply, all the rest are working so proves it is all now working and the switch mode transformer has not suffered any shorted turns when it went pop! current just driving the board 60ma (or there about's) so no nasty surprises when it gets connected to the mains transformer!

IMG_2721.jpg

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OK so another! this time a MK1 psu! this had C5 burnt up and connector where one pin had burnt out of the pcb!

IMG_2823.jpg.dd1260ec683de696738fdffe01c9c480.jpg

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so capacitors C5 and C6 removed and the area cleaned up from the burn! these are not needed so no need to go back!

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so I have connectors with the right pin but not the right housing!

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so damaged pins removed

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and a pcb eyelet put into the hole on the PCB so it gives more strength and a nice base to solder the track onto which most likely the through hole plating has been burnt away anyway!

top and bottom side

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next was DP6 in the -12v line was bad so removed!

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and replaced

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total of bits removed from the board

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and yes board now works great!

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after a nice clean up and solder resist it is all good to go again!

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Beautiful work Andrew as per usual :clap: :clap:

 

My Simpsons Lives again thank you so much 😄

Edited by matrixnetuk

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