ElectroVoice Q-66 amp schematic?

[nosaj]

Got an ElectroVoice EV-66 that was given to me and seem to be having problems finding a schematic for it. All I can find is this http://www.liquidx.nl/media/download...versterker.pdf

So far I have found 4 bad output transistorsTO-3(3 x MJ15023 and 1 MJ15022) a dead 20A fuse. The Output transistor were only on one channel. What I would like to accomplish is to find a way to bring up the other channel to see if it is working ok before proceeding further. On the bad output side I have all the output transistors removed. I also removed
a MJL3281A(CQ0347) a MJL1302A(CQ0333) and a C4793 these all test ok as do the ballast resistors.
Would I be able to fire this is up in this state to check out the other channel?


I will call Electrovoice and see if I can obtain a schematic from them.
Thanks for any insight,
Ok found it on this link http://music-electronics-forum.com/t34183/
nosajElectroVoice-Q44_66 pwramp.pdf
Attached schematic

[The Dude]

Electro-Voice Q44 & Q66 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

[nosaj]

Does anyone know how I might accomplish this?

What I would like to accomplish is to find a way to bring up the other channel to see if it is working ok before proceeding further.

Thanks,
Jason

[nosaj]

I would like to know if I can just remove the driver transistor to disable the poweramp section with out burning up resistors? I'd like to know so that in the future I can use the techhnique to troubleshoot other channels.

Thanks,

nosaj

[Jazz P Bass]

Not too sure what you are 'afraid' of.

How about repairing the blown side.

If you get the output section to the point where you feel the need to remove the output finals, you can insert one 1K 1W resistor from B to E on each polarity rail.

Other than that, it's down to basic troubleshooting.
Use your tools.
A variac, a lamp limiter, a few volt meters and finally, your brain.

[nosaj]

Not too sure what you are 'afraid' of.

How about repairing the blown side.

If you get the output section to the point where you feel the need to remove the output finals, you can insert one 1K 1W resistor from B to E on each polarity rail.

Other than that, it's down to basic troubleshooting.
Use your tools.
A variac, a lamp limiter, a few volt meters and finally, your brain.

Well when I order parts I'd like to do it once. the outputs I will have to order. When I last brought amp up on lightbulb limiter with all parts still installed There was a short. Well I check the outputs and found 4 blown outputs on the one channel. Will powering up the amp with the blown outputs removed damage any other parts? Or amp I safe to power up the amp ?
I want to bring the amp up to see if the other side passes sound. Since it was given to me i am the customer who spends the parts money. That's all. It seemed some other peavey thread Enzo had suggested to someone they could remove a resistor or a transistor I think so that the other channel could be tested. Just trying to avoid 2 parts orders.

Thanks so much,
nosaj

[olddawg]

You should be able to run the amp with outputs removed and with no load if there are no other shorted components. But as was said, the proper way to do it is to bring the voltage up slowly on a variac while watching the current draw. It's difficult to work on discrete large power amps without the proper tools. Lightbulb limiters are fine for tube stuff and old CRT TVs, but become problematic with modern equipment.

[nosaj]

You should be able to run the amp with outputs removed and with no load if there are no other shorted components. But as was said, the proper way to do it is to bring the voltage up slowly on a variac while watching the current draw. It's difficult to work on discrete large power amps without the proper tools. Lightbulb limiters are fine for tube stuff and old CRT TVs, but become problematic with modern equipment.

Ok, I can do that on my BK powersupply but it's only good up to 4 amps. Should be ok just to power it up I'd think if not I'll be replacing a fuse on the power supply. I've never seen an amp with a 20A fuse before.

nosaj

[nosaj]

Ok, I can do that on my BK powersupply but it's only good up to 4 amps. Should be ok just to power it up I'd think if not I'll be replacing a fuse on the power supply. I've never seen an amp with a 20A fuse before.

nosaj

If that proves fruitful then I'd just move some good outputs over to the bad channel an make sure that side works also.

I'll also have to build a larger dummy load as the one I have is good for about 300 watts. I was thinking and old Stove element immersed in some mineral oil might prove a worthy load.
Cause I also have a 1300watt amp to test.
Thanks,
Jason

[Jazz P Bass]

In my limited experience with power amps, it is perfectly o/k to test an amp at 1/2 power.

Full power load tests I use when setting current limiting circuits. (ala QSC)

[olddawg]

Ok, I can do that on my BK powersupply but it's only good up to 4 amps. Should be ok just to power it up I'd think if not I'll be replacing a fuse on the power supply. I've never seen an amp with a 20A fuse before.

nosaj

I couldn't read the schematic on the schematic on my phone, but if the unit uses a protection relay you may have to jumper it for tests until you can operate the unit with full voltage.

[J M Fahey]

Do not mess with the working side, specially do not remove good parts from it just to test tha bad one just to save some postage.

You should be able to cut power to the good side, either by pulling some connector or cutting some tracks, so you deal exclusively with the bad side until fully repaired.

Or viceversa, cut power to the bad one so you confirm the good side works well.

Order extra power transistors, they are not expensive and if not needed today keep them for future repairs on this or other amps, they are general purpose "universal replacements".

Also order extra ballast resistors , drivers, MJE340/350 , etc. you are not wasting a cent you spend ; in any case your time is worth way more than what a few spare parts cost.
And itīs not as if you were ordering an extra power transformer "just in case"

[nosaj]

Do not mess with the working side, specially do not remove good parts from it just to test tha bad one just to save some postage.

You should be able to cut power to the good side, either by pulling some connector or cutting some tracks, so you deal exclusively with the bad side until fully repaired.

Or viceversa, cut power to the bad one so you confirm the good side works well.

Order extra power transistors, they are not expensive and if not needed today keep them for future repairs on this or other amps, they are general purpose "universal replacements".

Also order extra ballast resistors , drivers, MJE340/350 , etc. you are not wasting a cent you spend ; in any case your time is worth way more than what a few spare parts cost.
And itīs not as if you were ordering an extra power transformer "just in case"

Well just got your reply Juan because I was going to update on where I was at. I put everything back together minus the 4 bad transistors. I am passing signal on Ch A ( just a xlr microphone hooked up to input) and it had a fair amount of volume.
The thing I am not sure about is how much input voltage should I run into it to see where output is?( I'll have to cobble up an adapter to hook up to my signal generator.

nosaj

[nosaj]

Now no output.
I'm having some problems with this EV Q66 I replaced the shorted TO-3 transistors and the bridge /mono switch. Still no audio output.
I took some measurements, but reall not sure which area to go. Front lights show chan A is still in protect mode. ChB is ok based on LEDS

Measurements are BCE

Q324 -1.13 -84.7 -0.5
Q316 -0.5 1.17 -1.14
Q323 1.13 84.8 0.57
Q123 -83.5 84.4 -83.6
q124 -80.7 -83.6 -82.9
Q110 -79.1 -77.8 -77.4

Any help will be much appreciated.

Thanks,
nosaj

[MarkusBass]

Measurements are BCE

Q324 -1.13 -84.7 -0.5
Q316 -0.5 1.17 -1.14
Q323 1.13 84.8 0.57
Q123 -83.5 84.4 -83.6
q124 -80.7 -83.6 -82.9
Q110 -79.1 -77.8 -77.4

Have you looked at the voltages and compared them with expected values? It's clear that some of them are completely wrong. For example: -83.5V on base of Q123, or -79.1V on base of Q110.
The question is which voltage is the best to look at? I would start with -79.1V on base of Q110. The base is tied with 1k resistor to +15V voltage rail. So such a voltage is almost impossible unless the D105 diode has failed or the R127-R135 resistors are open, or R143 is open. Can you check it (do you have +15V on D105 and R143 is not open)? Of course, failure of Q104, or Q106 can also cause the problems.

Mark