Author Topic: Musical Fidelity F15 repair "nightmare"  (Read 1393 times)

Offline Gerlach

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Musical Fidelity F15 repair "nightmare"
« on: November 25, 2020, 10:29:03 AM »
Lets start with this question first, who on this forum try to repair a Musical Fidelity f15 before?






Ok, so I got my hands on a F15, well the one that was posted 2/3years ago on the forum that I requested a person to do the repairs on the left side channel for someone. Repairs was done by local in cape town but cost a pretty  :2c: :2c: . This amp end up by last month. The owner gave it to me after the Right side channel went belly up and don't want it anymore. It will play for 15/30sec normal and then it will go super loud on the right channel but the left channel is stable and play normal level.

Open the amp and hooohoooooo, it's crazy inside. It's like a lucky packet. This amp in his life time went up to JHB for repairs/upgrades to what I founded out by old owner, and the repairs the person did in cape town side 2/3 years ago and he informed me to that there was some crazy stuff done on this board and the tracks was coming loos of age. This amp was build in 1993.



Right side channel.


Left side channel:


I Check the output terminals on the rights channel, 16v!!!!!  :sweat: left channel. 0v. try to adjust the the offset but can only get it down in to the 12v range. Not good. the Right side channel gets super hot to and fast. So I pulled the amp apart to see what's going on and to check for dry joints, didn't look good either there and you can see they try to save some of the tracks . Re-solder some joints just to check if I can safe it this way, start the amp up, no good. The 2 of the 4 10w resister on the PSU gets super hot, if I disconnect the right side channel wiring from the board, then it runs cool with no problems. Left side and right side rail shows +- 46v on both sides and is stable from the PSU side.







Well, if you cant find a 10w resister, lets slap one together. Will replace all 4 resisters with new ones.


Ok, next step, duplicate everything from the left channel that's working to the right side channel and see if I can get it sorted. So the parts arrived on Monday, busy de-soldering and testing with the multimeter and replacing as I go. I spotted that the one MJ15004 is showing open circuit so my guess is it started there. Other problem, with the age of the board, the tracks is busy getting loos when you de-soldering stuff, so it looks like I will have to run on some spots point to point wiring to help. Will give progress report as I go to see if I can get the right channel fixed. 




Funny thing was, this is a F15 amp but it's running the A1000 boards. You can't really find info on this amps on the net. You will find photos with two different boards and even 3de on to. Got in contact with JC repairs in the UK side. The F15 first addition came out with A1000 boards in there first addition , this the one I got, then the second and 3de addition used f15 redesign boards. The Pre and PSU shows F15 on them on my one.


You can find Clone boards online and blank boards for this unit but the problem is, the rated volts for them are 24-26V. 

Oooooo yes, and Thanks for @fredeb for his help and info to.

 
« Last Edit: November 25, 2020, 10:42:10 AM by Gerlach »
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Offline Orcish75

Re: Musical Fidelity F15 repair "nightmare"
« Reply #1 on: November 25, 2020, 12:30:05 PM »
Really hope you manage to fix it, will be a terrible loss if it gets binned.

Offline Gerlach

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Re: Musical Fidelity F15 repair "nightmare"
« Reply #2 on: November 25, 2020, 12:54:25 PM »
I hope so to. When I got it back 2/3 years ago I had for 2 months to test it out before sending it off to the owner and it sounded really good.

I'm waiting for responds back from this guy https://www.aliexpress.com/item/4000730788012.html to check what sort of volts rating the board can take. Maybe this board is drop in and go.



There this one to: https://www.aliexpress.com/i/32892756110.html

Good drivers have dead flies on the side windows. (Walter Röhrl)

Offline pwatts

Re: Musical Fidelity F15 repair "nightmare"
« Reply #3 on: November 25, 2020, 01:15:17 PM »
Gosh these aliexpress boards are gorgeous - now if only nothing on them are fake.....

Offline GECO

Re: Musical Fidelity F15 repair "nightmare"
« Reply #4 on: November 25, 2020, 01:35:25 PM »
judging by printing on the transistors, it would make me very cautious.

Offline Gerlach

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Re: Musical Fidelity F15 repair "nightmare"
« Reply #5 on: November 25, 2020, 01:49:39 PM »
judging by printing on the transistors, it would make me very cautious.

Hahaha!! jip!!!! they are super off center. And the original isn't cheap. 8 of them in my order was more then half of cost of my order of all my parts that order to check if I can fixed that old board.

Gosh these aliexpress boards are gorgeous - now if only nothing on them are fake.....


Yes, that black and red looks super nice. And I can bet you if there is instructions with, then I need to go buy some Rise  :giggle:
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Offline Gerlach

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Re: Musical Fidelity F15 repair "nightmare"
« Reply #7 on: November 25, 2020, 02:05:56 PM »
Got the diagram, it was all the time in front of me. Corner of the board stand PCB by netwarm2009. Here is al the info : http://bbs.hifidiy.net/thread-317411-1-1.html

Good drivers have dead flies on the side windows. (Walter Röhrl)

Offline Orcish75

Re: Musical Fidelity F15 repair "nightmare"
« Reply #8 on: November 25, 2020, 09:43:56 PM »
Excellent!  :thumbs:

If you can get the Gerber files, you can send them off to JLCPCB https://jlcpcb.com/ and get 5 boards for less than $20. It looks like the board is around 100mm x 200mm. The only catch is shipping, might be expensive as they won't send via the post office.

Offline 1200GXman

Re: Musical Fidelity F15 repair "nightmare"
« Reply #9 on: November 26, 2020, 08:16:32 AM »
Very strange that the tracks would come loose due to age. Do you guys think it was just bad quality used in the batch because there are lots of vintage amps floating around that still have nice tracks.
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Offline handsome

Re: Musical Fidelity F15 repair "nightmare"
« Reply #10 on: November 26, 2020, 08:46:15 AM »
Tracks should only lift from heat - either over exhuberant soldering irons or too much current - especially on 'modern' PCBs. As you say even on 60s era PCBs the traces are firmly glued...until you try removing/replacing components

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Offline Gerlach

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Re: Musical Fidelity F15 repair "nightmare"
« Reply #11 on: November 26, 2020, 10:43:50 AM »
Tracks should only lift from heat - either over exhuberant soldering irons or too much current - especially on 'modern' PCBs. As you say even on 60s era PCBs the traces are firmly glued...until you try removing/replacing components

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Very strange that the tracks would come loose due to age. Do you guys think it was just bad quality used in the batch because there are lots of vintage amps floating around that still have nice tracks.


I think it can maybe heat or bad batch of boards and over current. This amps where famous between the forums and users for heat because it's a 100w Class A amp, other think, I think the board is maybe taking a lot of current because the board was design for the A1000 that was running a smaller PSU and making about 50watt in Class A, know it it's running a bigger PSU with a big toroidal. You can actually see in the white pc board how the color change because of the heat.

Every spot where de-solder, I find a track maybe getting loos.

Here some web photos of the deferent boards the F15 came out:

The A1000 amp, close design like mine but this one don't have the off set pod.


The A1000 amp, same board like mine with offset pod on both boards that my F15 is using.




This is how the F15 version 2 board looks like.


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Offline Hi-Phibian

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Re: Musical Fidelity F15 repair "nightmare"
« Reply #12 on: November 26, 2020, 10:52:27 AM »
Tim De Paravicini in an interview I read in the early nineties called it Musical Fiddle Tea.   
Over the years they have made some amazing sounding kit but a few techie people I know also know some of their models to be the most challenging/stupid repairs.   

They are kind of known to put too much heat in too small a box at times. 

Getting back to tracks, I also just suspect multiple repair attempts.   Some boards are much worse than others but until repair is needed most are stable. 


 
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Offline Gerlach

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Re: Musical Fidelity F15 repair "nightmare"
« Reply #13 on: November 26, 2020, 11:47:50 AM »
Tim De Paravicini in an interview I read in the early nineties called it Musical Fiddle Tea.   
Over the years they have made some amazing sounding kit but a few techie people I know also know some of their models to be the most challenging/stupid repairs.   

They are kind of known to put too much heat in too small a box at times. 

Getting back to tracks, I also just suspect multiple repair attempts.   Some boards are much worse than others but until repair is needed most are stable.

Somewhere I read on a Forum, that the problem was in the 90's that was going for mass production and not quality production, so there was a lot problems over time. There is a guy in the UK that I spoke to that's the main guy for repairs on this units. https://jsaudiorepairs.co.uk/ . There some nice stuff on his FB page.

I actually got F22 valve pre that coms with it that I'm using and it works really nice.
Good drivers have dead flies on the side windows. (Walter Röhrl)

Offline pwatts

Re: Musical Fidelity F15 repair "nightmare"
« Reply #14 on: November 26, 2020, 12:02:36 PM »
Doing your own boards would be fun but expensive: you will preferably want to use 2oz copper and together with shipping it will end up north of $100 before VAT.