Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems DSP life expectancy

Do you mean replace a faulty amp with like for like, or remove and replace with some sort of upgrade/different manufacturer?

Like for like.

But would also be open to suggestions for alternate options.

Like for like is straight forward. Probably take no more than 30 mins.

6 small wires from the DSP board soldered to PCB pins on the amp, so easy to remove. Just slide back the heat shrink on each carefully.

5 cables going to the rectifier board with the two large capacitors. Slight harder but with a suitable soldering iron should be no problem, just more area to heat up.

3 screws holding the heat sink to the panel.

We've done about 10 out of 15 speakers so far. Took 10 days before they even shipped the part out.

If your speakers are 24/96 with older 7 Segment Display I can almost guarantee your resistor is toast and the board damaged.

Some Matrix Display units (later ones) have the 330 Ohm 4 Watt and some don't (earlier ones). 4 of mine had the 330 Ohm 4 watt and looked perfect and 4 looked just like the 7 segment display models (i.e. toasted).

Every one with "brown" resistor had damage to the board. And getting the toast ones out was not easy with out further damage, due to warping and swelling of the board in that area.

The two 18 bit I have left also looked good, but that was a small sample.

Out with the old in with the new.



I mounted them a bit above the board so as not to use the board as a "heat sink" any more.



Nice looking factory fit.



All of them needed rework like this. Some needed rework on both.

Really helpful stuff George, great photos. Many thanks.

Cheers

George

New resistors look to be very close to capacitors - maybe arrange bigger gap? Also 4 watts is quite a lot of heat to dissipate for the small resistor area, a small metal heatsink might be useful.

Was also looking at thread about G95 failure, and wondering if surface mount components are a good thing from customers point of view. Having everything repairable would be my ideal, and the thuoght of some DSP8k's becomoing un-repairable for want of a chip, say, is worrying.

Locus

The resistors can withstand 4 watts, doesn’t mean they will have to dissipate that much.
Resistance was dropped too.

We did what Meridian did with the latest version, which seem to hold up fine.

The larger wattage resistor will have way more surface area to dissipate half the wattage.

We plan to measure temps.

Testing Testing 1,2,3 Testing.

With Original 680 Ohm 1? Watt Resistor

Ran Pink Noise 1 Hour at 65 Level with Speaker Closed up.

Measured 12V Across the Resistor that Cooks (Negative Side of the 45V).
Both the Regulator and Resistor were around 137F (close to 60C).

That does not explain the Temps/Conditions needed to Burn Resistor and the Board.

But it was still climbing slowly after 1 hr (and it climbed slowly the whole time). Room was fairly cool.

With New 330 Ohm 4 Watt Resistor

5.7V Across the Resistor
Regulator is about the same at 139F after 1 hr, Resistor is now 123F

Oh my friend found conflicting info in the Data sheets that the regulator is limited to an absolute 37V input vs it's limited to 37V difference between input and output. If it was absolute spec the 330 ohm raises the voltage and puts the input slightly out of spec (39V). With relative spec it's (39V input - 15V output) which is well within spec.

How easy is it to view the offending resisters?

Im thinking of selling my 5k's and don't want to do so without checking the condition of the resisters and replacing/discounting if necessary - would rather someone else did any replacement but looks like in UK options to repair legacy kit is getting limited.

Before I purchased these, the person that I purchased from said that they were serviced by a dealer so hoping that they are all good.

It is quite straight forward to check the resistors.

1) Unplug from power
2) Lie them flat on the front (carefully)
3) Undo the screws holding upper part of the back panel
4) Gently lift until you can peak in and see the condition of the resistors. Be careful there is the power connector at the lower end and the display connector at the top and the connector to the speaker drive units in the middle
5) If you want to take a closer look the three leads mentioned above will need to be disconnected.
6) Refitting is the reverse of the above...

This won't tell you the condition of the PCB underneath but will give you an idea.

You shouldn't need anyone specialized in "Meridian" to do the repair. Any competent repair shop should be able to handle it.

If the resistors are not brown, I suspect your PCB board is fine.

Even with burned Resistors the PCB was often fine, it's the process of removing them that does the most damage to the PCB traces.