Fostex PM-1 Repairs Help Wanted !

[db133]

Hi

My name is David I live in Brighton Sussex UK.

Just joined up so 'hello' to all.

I have a pair of Fostex PM-1 studio monitors that I have 'over cooked I think'.



I can solder and I have a meter.

Can some please help me to repair them please ?

 

[db133]

Where has my item gone ?

 

[db133]

Its back, thanks.

 

[db133]

Where has my item gone ?

Its back don't worry.

 

[db133]

Up date.

 

[db133]

4 areas for investigation, where do I start ?

 

[PetruV]

The chips on the heatsink,change them if theire burnt out

 

[db133]

Sorry to be a novice ! Which ones are the chips ? how do I know if they are burnt out ?

Thanks for you input, much appreciated.

 

[iaxxaxxai]

They are the large-ish multi-legged pieces attached to the heatsink and labeled "IC4" and "IC5" on the circuit board. Not sure how you'd check to see if they're burned out apart from just replacing them outright. Maybe someone else can give advice for checking them. Fortunately, they appear to be LM3886, which aren't particularly expensive or hard to find.

What exactly are the symptoms? Is it just not making any sound? Or is it making sound, but it's bad?

 

[db133]

Yes they are LM3886.



The symptoms : 1 speaker is dead and the other is making a bad noise and pushing the large speaker out.

Thanks for your input much appreciated.

 

[db133]

I have just found a data sheet at Farnell's with test circuits 1 for DC and 2 for AC.

I don't understand them yet but trying to learn.

 

[POX]

Hi i have the same speakers and the same problem. Would like to try and fix, but I have no clue where to start, other then the fuse. Did you fix your speakers? Any advice you could share? thanks...

 

[4teenth]

I also had a problem with the high frequencies distorting at anything below a very low level, so I decided to grab a couple of the LM3886 chips and try to replace.

Now I have no tweeter at all and distorted low end...😡

I'm going to have another look this afternoon...

 

[4teenth]

So I carried in investigating, swapping the chips over ( with one of them burning out in the process.. oops) to no avail. . I was about to give up, but i thought 'what the heck' and cracked open my other fully working monitor. Connecting this gave me the same result, and hooking my 'broken' amp to the working cabinet reeked in a working monitor. So god knows how, but somehow in fixing the amp I blew both the drivers. Replacements come in above the going eBay rate for a single working monitor, so I'll bide my time, unless anyone here wants to sell their faulty units? (Provided the drivers are good, of course. ..)