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midibob

JPM MPS1 RIFA's

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44 minutes ago, Andrew96_ said:

Setting up VR3 is a bit of a challenge!

58C900A7-9EA1-478B-817D-41FB9F5397E8.jpeg.800e2de5852235ab31f7a5f4ff64fb98.jpeg

So i have to ask the noob lazy question, can you set them up and then sell them to noobs like me so i can solder it into mine or is it not that straight forward? That looks difficult 😂

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11 hours ago, Andrew96_ said:

Setting up VR3 is a bit of a challenge!

58C900A7-9EA1-478B-817D-41FB9F5397E8.jpeg.800e2de5852235ab31f7a5f4ff64fb98.jpeg

Jesus that looks difficult! I bet that has taken some time! 

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Just getting them to sit nicely (open) on a desk is a challenge - wish they'd made the boards unplug - looks pretty organised.

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13 hours ago, Bricey21 said:

So i have to ask the noob lazy question, can you set them up and then sell them to noobs like me so i can solder it into mine or is it not that straight forward? That looks difficult 😂

No you cannot, the various component tolerances in each unit will be a little different.

However, I think it is fair to say you could put the new VR3 in around the same position as the original AS LONG AS IT HAS NOT BEEN MOVED and it could be close enough.

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The external power supplies are needed to supply the pcb and adjustable to be able to be set so when the undervoltage limit is set VR3 can be set to turn off  the 5v before it's input drops below the threshold.

34 minutes ago, quattrohead said:

No you cannot, the various component tolerances in each unit will be a little different.

However, I think it is fair to say you could put the new VR3 in around the same position as the original AS LONG AS IT HAS NOT BEEN MOVED and it could be close enough.

yes you could just set it where the old one is, BUT unless it is EXACTLY the same make of trimmer then it won't actually be the same even if set in the same place! that's the nature of trimmers! When I set the new one to the same as the old one I found the shutoff of the 5v was far to low! well below the threshold needed, I had to back it off from that. but each to there own,  I guess over the years when these are replaced they are just set to whatever the repairer thinks, this game is all about getting things working, not necessarily if it is right or not.

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Old against new, clearly set differently, but now the 5v shuts down correctly 

6C2E27F0-A018-4E69-8F64-C37FD2EF7D6E.jpeg.11e60aa0e10ff898b1d299035769f2a4.jpeg

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4 hours ago, MikeB said:

Jesus that looks difficult! I bet that has taken some time! 

Mike it is just a case of setting things out and making sure nothing can short out on anything else, the external variable power supplies I have connected means it is easy to set Undervolts cutoff point, so looks more impressive than it actually is!!! Also I discovered the 12v regulated was working fine when powered by my external power supply’s but when the psu is connected to the mains the 12v only reaches 10.2v ! So still not out of the woods yet !!

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As I have always said it is the electronics that interests me so I like to work it all out how to do these things correctly. 

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Posted (edited)

You have given me a kick to check over a couple of my mps power supplies, on one of them I am missing 5v on all 5v plugs, am I looking for something simple or could it be any number of things?

Okay I’m being thick! Just read back through the thread, and 5v failure is going to be the VR3! 😂😂

Edited by MikeB

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well I think I have cracked the low 12v issue which is only giving out 10.2v! the colour of the supplies are as follows, 2 YELLOW wires from the transformer to the pcb are for the 12v line! 2 ORANGE wires from the transformer to the pcb are for the 5v line....

 

simple enough, the MPS2 manual contains the transformer connections....

colours!.jpg.8e15ef6167abde6d2dd659217e51298d.jpg

 

I decided to measure across the yellow wires on the transformer, 30v AC , OK I thought, measured the yellow wires on the pcb..... 18.1v AC.... huh......... that's weird!!! why the difference!! somethings here is odd!!! so went to the small fuse board between the transformer and the main board, it then became clear, can you spot it?

IMG_0619.jpg.589a620db8ba20978cb2cb13ec1afe12.jpg

for some really odd reason the wires are swapped over AT the fuses!!! ORANGE goes to YELLOW once through the fuses, and YELLOW goes to ORANGE! 

so I guess someone had been inside it before me and pit the wire colours correct according to the MPS2 manual, I am guessing here but think this being the yellow label psu is from a earlier MPS1 era but I don't have the mps 1 psu manual to check!

the wires don't look like they have been touched with a soldering iron since it was made!

Taken at leas a day to get this far and work this out! I guess no one is looking for crossed over wires from what the manual tells you! 🤣

 

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Wires swapped over so YELLOW to YELLOW and ORANGE to ORANGE

C46616F7-638D-491C-B779-F10A9077C434.jpeg.f65aff645cb0aebbf7c8d56b9b1f407a.jpeg

 

SUCESS!  12v now perfect!!!

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-12v is also good too! Will put the psu back together tomorrow!! Well later on as it is 1:24am!

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New top cover made from perforated metal sheet bought off eBay ( I figured they cannot fake that on eBay) and all back together now!!

so rifas, and VR3 replaced and faulty crossed wiring sorted! front plastic and top cover made!

not as easy repair as I thought it was going to be but I do tend to find things I repair tend to be the worst compared to others on here! It is my luck lol!!
 

It is now ready for my MPS test rig!! Yay!!!

 

10701BB1-3A9D-48FB-8F04-151E846418E3.jpeg.5c11cbacb38dd0ef52e4b6d831ee4298.jpeg

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Andrew do you have a link to the voltage regulator that you used please?

 

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Like the new top cover. I assume you had to trim it to fit? I'm thinking sharp edges here, did you use a smooth file to finish it?

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4 hours ago, MikeB said:

Andrew do you have a link to the voltage regulator that you used please?

 

Hi Mike, I presume you mean VR3 the trimpot, The supplier only sent 6 instead of the 25 i purchased so waiting for them to rectify this before I tell anyone where to get them from as I don't want to be responsible for anyone getting ripped off until I get my complete order. I do find RS will do ones that fit perfectly  from there specifications but buying just one and then p+p on top makes them expensive, but I think there are the right specification

https://uk.rs-online.com/web/p/trimmer-resistors/5222479/

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48 minutes ago, midibob said:

Like the new top cover. I assume you had to trim it to fit? I'm thinking sharp edges here, did you use a smooth file to finish it?

yes it was a perforated sheet of stainless steel as that was the cheapest and I thought that won't rust either!

https://www.ebay.co.uk/itm/Stainless-Steel-Round-3mm-Hole-x-5mm-Pitch-x-1mm-Thick-Perforated-Mesh-Sheet/133402841178

 

I selected 500mm x 200mm sheet and cut 20mm off the side and 100mm off the length with a hacksaw, ground the edges down with a bench grinder and then a file. It was tougher than I thought so suggest getting aluminium sheet or a type that is easier to cut and bend! stainless looks good but was a bit of a bugger to work with!! I had to make a cover as the power supply I got did not have one!

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8 hours ago, Andrew96_ said:

Hi Mike, I presume you mean VR3 the trimpot, The supplier only sent 6 instead of the 25 i purchased so waiting for them to rectify this before I tell anyone where to get them from as I don't want to be responsible for anyone getting ripped off until I get my complete order. I do find RS will do ones that fit perfectly  from there specifications but buying just one and then p+p on top makes them expensive, but I think there are the right specification

https://uk.rs-online.com/web/p/trimmer-resistors/5222479/

Thank you Andrew, I will get one ordered. 👍

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@Andrew96_ legend, i now have mine up amd running again, lovely to see a classic machine boot up for the first time, thank you so much for your help and great write ups

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