The Workbench

Re: Beomaster 8000 check-up/LED protection?

Premiumverum — Mon, 21 Jun 2010 11:38:52 GMT

Hi Frederik,

Thanks for the advice! I already had a quick check of the power amps, they looked fine so I trust them. Next weekend it is time for the big overhaul. I came up with a question for you, check your thread!

Re: Beomaster 8000 check-up/LED protection?

Mohawk — Sun, 20 Jun 2010 16:11:57 GMT

Hi and congrats to your BM8000 :D

Check the soldering of the carbon composite resistors in the output amps in particular, these resistors run hot during operation and cause the joints to break. Even the PCB tracks can break around the solder pads of these resistors probably due to age and heat.

I wouldnt run the BM until this is checked. Remember there are lots of power involved here, and if anything goes wrong a lot of damage can happen!!!

/Fredrik

Re: Beomaster 8000 check-up/LED protection?

Dillen — Sun, 20 Jun 2010 04:39:55 GMT

Caps, output stage trimmers and cracked solder joints first.
If it still has issues, they will be much easier to diagnose by then.

Martin

Re: Beomaster 8000 check-up/LED protection?

Premiumverum — Sun, 20 Jun 2010 03:53:02 GMT

Ah I see, the spring pressure is the other way round, it presses the wire's tip onto the trace! Quite logical actually!

Thank you for helping me understand Martin!

PS: I was listening to the mighty beomaster while typing this, it just gave a loud crack through the speakers. Third time that happened already! Guess I'd better make haste with the recapping, or is this more likely due to something else?

Re: Beomaster 8000 check-up/LED protection?

Dillen — Fri, 18 Jun 2010 14:36:23 GMT

The ones I have seen (many) all had the wire resting with a very gentle spring pressure on top
of the opposite trace (not soldered).

Martin

Re: Beomaster 8000 check-up/LED protection?

Premiumverum — Fri, 18 Jun 2010 03:29:58 GMT

Hi Martin,

Thanks! I drew a little picture, if I understand correctly the LEDs are soldered with their base to the + side of the PCB. and the little wire is hooked like a spring behind the edge of the - trace on the PCB like this?

Re: Beomaster 8000 check-up/LED protection?

Dillen — Thu, 17 Jun 2010 05:33:28 GMT

The little wire is a form of stainless steel. The wires usually don't break but they lose the spring tension that presses them against
their PCB pad.
Even conductive paint won't hold on to it and conductive glue is expensive and
will easily make a mess. I've tried both.
Cheaper and easier to have them rebuilt, the only downside is that all four displays need to be done to achieve uniform
light output and segment color.

Another thing is that it is extremely difficult to do anything to a display, even solder it in or out, without disturbing more
LED junctions. The vibrations alone will easily do a lot of damage and if you take the display apart it will be extremely
vulnerable to touching etc.
I have rebuilt many of these displays (yours are also welcome here). Depending on the type of display and the
new LED's, I like to use solderpaste and hot air soldering. The rebuilt displays are then tested, sealed and practically indestructable.
It's not impossible but it's a tedious job and requires a steady hand, very rewarding none-the-less.
A microscope is a must in any case.

Martin

Beomaster 8000 check-up/LED protection?

Premiumverum — Thu, 17 Jun 2010 05:17:53 GMT

Hello fellow Beo-cravers,

A dream has come true: I recently bought a beautiful, massive, powerful BM8000!

It works perfectly, except for intermittent disfunction of a couple of leds, probably due to faulty connections of PCB.

I want to make it ready for the future, so when my final exams are done next week I'm going to give it a check-up:

- Fresh electrolytics

- checking/fixing broken connections

- checking amplifier no-load current and offset

Anything else that needs special attention in these machines?

Also, I'm worried about the display LEDs. They funtion OK now, but I wouldn't like to have to replace any of them, they are very small and my soldering iron is very big in comparison! Doubt I can do it myself.

After reading this post, rebuilding BM8000 displays, I wondered: the problem seems breaking of the little wire that connects the LED to the PCB. What if you fixate this little wire to the PCB with a careful drop of transparent glue? Might protect LED function in the future. Good idea? Or will it make the LED overheat because the glue will impair cooling or something?

Your opinions/remarks are most welcome!