Yamaha EMX2000 Conversion to Passive PA

[RandomJRogers]

Very little info supplied so far, but it looks like te power amp, or *maybe* the power supply is damaged, and blowing fuses.
IF so, new fuses will also blow, unless you repair the main problem.
Blowing fuses is a symptom, not the cause of the problem.

If your mixer is built as 3 well separated systems, such as preamp/power amp/power supply, then you might unplug just the power amp board and run just the mixer, fed from the power supply, canīt be more precise until somebody posts the schematic.

Just to save time, search for it and post it here.

F103 is the fuse that has burnt out (thanks for the schematic)- 1A 250V- I don't seem to be able to order this fuse (5mmX20mm) unless it is a 250VAC.
There is obvious damage to D115 and D116 caps on the power amp board but I don't know where to start to find out why the F103 fuse is blowing- any help?
And what kind of power supply would I need just to run the pre-amp/mixer desk? That is actually my first priority as I plan to separate the power amp from the mixing desk.
I have cleaned the pots and sliders and everything is moving nicely- one potentiometer (Effects Monitor1) had some severe rust/corrosion and may need replacing but everything else looks good- https://youtu.be/ILkn7fxp5uQ

[Enzo]

F103 is the fuse that has burnt out (thanks for the schematic)- 1A 250V- I don't seem to be able to order this fuse (5mmX20mm) unless it is a 250VAC.

I don't understand the problem, you need a fuse rated for 250 volts, and all you can find are fuses rated for 250 volts.

[Leo_Gnardo]

F103 is the fuse that has burnt out (thanks for the schematic)- 1A 250V- I don't seem to be able to order this fuse (5mmX20mm) unless it is a 250VAC.
There is obvious damage to D115 and D116 caps on the power amp board but I don't know where to start to find out why the F103 fuse is blowing- any help?
And what kind of power supply would I need just to run the pre-amp/mixer desk? That is actually my first priority as I plan to separate the power amp from the mixing desk.

Don't worry about the voltage rating on that fuse. 250V is the usual item.

If the damaged caps were replaced maybe the fuse would hold? It's worth a try. Age damages electrolytic caps - it may be a good idea to replace the matching caps on the other power amp.

If you disable or remove the power amps, the power supply you have will work just fine for the mixer. There are voltage regulators in it to run the preamp/mix department. The power supply will be relieved of its task running the power amps, so that's also a no worry situation. Why replace it unless you want to spend a lot of time & effort doing something you don't know how to do. Granted a smaller supply would reduce some weight. But is it worth the effort to save a couple of kilograms?

[RandomJRogers]

Here is the SM: [ATTACH]45288[/ATTACH]

Thanks!

[RandomJRogers]

Don't worry about the voltage rating on that fuse. 250V is the usual item.

If the damaged caps were replaced maybe the fuse would hold? It's worth a try. Age damages electrolytic caps - it may be a good idea to replace the matching caps on the other power amp.

If you disable or remove the power amps, the power supply you have will work just fine for the mixer. There are voltage regulators in it to run the preamp/mix department. The power supply will be relieved of its task running the power amps, so that's also a no worry situation. Why replace it unless you want to spend a lot of time & effort doing something you don't know how to do. Granted a smaller supply would reduce some weight. But is it worth the effort to save a couple of kilograms?

Yes, I think so- mostly because I want to use the power supply later if I do something else with the power amps- and I'm thinking the pre-amp/mixer will run on a pretty small transformer? I will look at testing/replacing any similar caps but I think I really need a variac to do any serious testing- would a 5A variac be sufficient for this job? These are the specs-

'Single Phase 200 to 250 Volts Variable AC Transformer output from 0 to 270 volts 1000VA 5 Amps'

-otherwise I would be keen to build the light bulb current limiter (does this function in place of a variac or an ammeter? I think my multi-meter will do the job of an ammeter, otherwise I can buy one if I think I'm going to be using it a lot)

[RandomJRogers]

Here is the SM: [ATTACH]45288[/ATTACH]

I just found the part number/s for the blown fuse and there are three different parts listed- none of them 1A 250V as was installed.
How do I know which of these is the correct part (page 66 of the above schematic)?
F103 (fuse)
*VS823400 (10.00A JUC)
*VV314500 (SIC(TL) 7.00A JU)
*VV071700 (TSD 3.15A 250V SEM)

[Enzo]

You look at the notes column. Now refer to the opening page of the parts list, page 37 of the file. The A is for Australia. SO you want the fuse with the A note, looks like 3A slow.

[RandomJRogers]

You look at the notes column. Now refer to the opening page of the parts list, page 37 of the file. The A is for Australia. SO you want the fuse with the A note, looks like 3A slow.

3.15A? I'd like to know what 'TSD' and 'SEM' stand for but that's definitely the right one. Cheers!

[Enzo]

I think SEM is short for SEMKO, spelled out in some descriptions farther up the page.

TSD is the type fuse, a time delay fuse, aka slow blow.

http://www.optifuse.com/PDFs/TSD.pdf

[RandomJRogers]

I think SEM is short for SEMKO, spelled out in some descriptions farther up the page.

TSD is the type fuse, a time delay fuse, aka slow blow.

http://www.optifuse.com/PDFs/TSD.pdf

All I could get at the electrical shop was a ceramic 3.15A fuse- I installed it and turned on the power- the power indicator light came on for an instant but nothing else.
Time to buy a variac?

[J M Fahey]

Build a lamp bulb limiter which is faster, cheaper, and "automatic".
if you still have a short (I guess you still do), it will harmlessly shine bright and let you do some measuring.
And you won{t blow fuses while testing.

[J M Fahey]

Just checked the schematic.
1) you certainly chose a complex amplifier to "start swimming" into Electronics.
Like being dropped in the middle of the Atlantic

2) those are Darlingtons, whicnh means replacing the power transistors automatically replaces drivers with them.
You might give it a try.

* replace the 3.15A main fuse
* plug amp into bulb limiter (use a 60/75W incandescent or quartz bulb)
* it will probably shine bright, indicating a short
* measure all power transistors for shorts, with amp unplugged from mains and after , say, 10 minutes so all voltages discharged. Just in case measure voltage across main caps.
With meter set to diode check, check for CE shorts at Q117-119-123-121-111-118-120-124-122-112 and replace any bad one.
Also check that resistors R131-132-231-231 have not blown open.
Just replacing blown power transistors might restore amp function.

The amp is more or less conventional, although Class F/G/H (never remember the differences) but an experienced Tech can repair it, the keyword is *experienced* , definitely not a project for a beginner .
You may try your luck at replacing the main suspects I mentioned above, they are less than $5 each at Digikey ... any more complex problem turns the amp into a boat anchor.

3) all supplies and power amps lie on the same PCB, so you can{t separate them.
IF you wish to disconnect the Power Amp and try to use the Mixer (plus effects, Phantom power, etc) on its own, feeding an external power amp, you have two "crude but simple" ways to avoid the dead power amp sucking all blood from your current power supply and blowing the main fuse:
a) remove the main rectifier bridge, D307
b) cut transformer wires leading to pins 4-6 on Connector CN102, coming from the power transformer.
Leave 2" pigtails on the connector, tape ends, same with transformer cable ends and tie them safely so they are not bouncing around, you cut main amp power feed but Mixer supply should still work.

Some day in the future you might repair that power amp or pay a Tech to do so.

[RandomJRogers]

I have made a neat little light bulb tester and my 100W globe is shining brightly- now I will start following the above advice. What are the chances that the power transformer has shorted?

[J M Fahey]

You can check it yourself, unplug the 6 wire connector CN102 which feeds both power amp and preamp supplies and turn amp on again, still through limiter.
If bright shining, the PT is kaputt.
If dark orange or red, thatīs the normal idle current pulled by any healthy transformer, no big deal.
In this case momentarily disconnect power amp feed by any of the methods suggested above, plug CN102 again into the main board and turn amp on (still through limiter), mixer Leds should turn on , in fact mixer "should" work, although maybe at reduced performance.
IF it works (hope so), plug mixer straight into mains, main fuse should not blow, and mixer should work properly, which was your basic goal.
You may then try to repair the power amp, now witfidence that effort wonīt be in vain.

It would be VERY frustrating to spend time and money to repair power amp and then find mixer section is dead or something, although I think it will work, the **abused** parts in any amplifier are Power Amp and then Power Supply.