Calling any of the Australian lads on here ...

I can't help you, I'm afraid. I've never serviced PA equipment. You might have better odds asking in aus.electronics, which is a pretty lively group. I've added them to the newsgroups line.

Supersonic oscillation maybe? Have you tried hanging a scope on the preamp output?

Ew.

Fair enough, too.

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------

Dodgy bias pot ?

Are we talking of the original Telex or another company ? Bosch picked up Telex along with EV, Midas, KT and Dynacord and technically DDA although they've dropped the brand.

Graham

: : :Arfa Daily wrote: : :> Anybody got any experience of an Audio Telex Communications of Sydney P.A. :> amp model AMIS 250 ? I am particularly looking for a copy of the schematics, :> but any help with it from anyone who knows the model, would be appreciated. :> So far I have only been able to find a user manual. :>

:> As it came to me, the main bridge reccy had one limb s/c, and the wires to :> it looked as though they had got pretty distressed from heat in the past. :> With the reccy replaced, it seemed to come up ok, but had no output. Signal :> is getting up to the front pcb from the rear one, and the signal presence :> detector for channels 1 and 2 is working, as the channels 3,4,5,6 mute relay :> triggers when signal is applied to Ch1 or 2. You can also see the signal at :> the detector opamp. But that's it. There doesn't seem to be any further :> preamp activity at all. There is an 'insert' jack on the rear panel, and :> this should carry preamp output, which it then links back to power amp :> input. There is no preamp out signal at this jack. Nor anything at the 'tape :> out' RCAs on the rear panel. :>

:> One further thing. Sometimes when you switch it on, the output stage very :> quickly runs very hot, and the bridge gets very hot, which I guess is the :> problem which led to the demise of the original, and made the wiring look as :> though it has got hot, so when this problem occurs, there's some serious :> current going through the output devices for some reason. : :Dodgy bias pot ? : : :> When it's doing :> this, there are no signs of any instability - in fact still no output of any :> description. I would add that this is a crap lead-free product, and every :> joint on the output board of course *looks* bad. I have not been able to :> provoke the heating up problem when it is running cool, by any kind of :> disturbance, but with lead-free, in my experience, that doesn't necessarily :> mean that the problem is *not* a bad joint, and that is still my gut feeling :> about it ... :>

:> So, anyone got any hints, tips or insights (or schematics :-) !!) for :> this model, please ? : :Are we talking of the original Telex or another company ? Bosch picked up Telex :along with EV, Midas, KT and Dynacord and technically DDA although they've :dropped the brand. : :Graham

AIUI Audio Telex is purely and Australian company. I vaguely remember buying something from them back in the late 80's. These days they are part of the Hills group

Yes, as far as I know they are an Oz company, and pretty well respected in the field of 100v line PA equipment.

All of which still doesn't help me with my problem / need for schematics ,,, :-\\

Arfa

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Some 7 or more? years ago Audio Telex took over the company, Australian Monitor, that at that time made good PA amps etc. to extend their product range.

I too found the user manual but then searched for service manual Australian Monitor AMIS250 250w 100v Mixer Amp and found this link....

It may be what you need.

Regards,

Don

ps. I once worked in the same building as them in a former job.

On Mon, 11 May 2009 04:27:20 +1000, "Don Richmond" put finger to keyboard and composed:

FYI, I notice that transistors V19 - V24 on page 10 are drawn incorrectly. Their emitters and collectors should be interchanged.

Here's a tip:

A Google search for ...

AMIS250 "service manual" filetype:pdf

... gets two hits.

- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.

Hi Don, thanks for the pointer. However, there's something strange going on here. Another guy contacted me off-group and had also found these schematics. Thing is that although they claim to be for an AMIS250, they don't match what is actually in the item. Let me just qualify that. The input board is spot on. Everything matches - schematic, layout, component numbering. The power amp is pretty damned close. Layout looks about right. Schematic looks about right. Component numbering is out the window, though.

Now the front panel mixer / preamp board. This is nothing like what is in the actual unit. The board fitted has all the same pots etc, but instead of the three ICs shown on the schematics and layouts, this version has no less than 12 ICs - two of those 8 pin in-line devices like NMJ1458, one 14 pin DIL, and the rest are 8 pin DILs. The layout is nothing like the one in the manual. In my trawling around the 'net for info, I have come across references to a "P" version which seems to be simpler. Maybe the manuals which seem to be available, cover this variant, rather than the one that's on my bench ? :-\\

Arfa

Hi Franc. These are the references that I keep coming back to. Regarding the first result that Google throws back, see my reply to Don in this thread. The second result is from the same site, but is actually for the AMIS120. This version actually has a much more complex preamp / mixer, but it is 8 channel rather than 6, and still doesn't even resemble what's in the one on my bench. Thanks for your efforts anyway.

Arfa

On Mon, 11 May 2009 11:03:04 +0100, "Arfa Daily" put finger to keyboard and composed:

Are we looking at the same diagrams? The mixer board on page 11 of the manual has a lot more than three ICs. For example, IC7 is a 28-pin PIC uP. The layout on page 14 has at least 7 ICs.

According to this URL ...

... the "P" version is a power amp while the plain version is a mixer/amp.

================================================================== Mixer/Amps: Integration

AMIS250

250 Watt Rackmount Mixer Amplifier (2RU) ? 70 volt, 4 ohm, balanced XLR & record outputs ? 6 x dual balanced mic/line inputs ? Phantom power on all mics with defeat switch ? Multi-level VOX muting from channels 1 & 2 ? Overall bass, treble & master controls ? Fan cooled for added reliability

================================================================== Amplifiers: Power Amplifiers

AMIS250P

250 Watt Rackmount Amplifier (2RU) ? 70 volt, 4 ohm ? Balanced line level input ? Current limiting ==================================================================

- Franc Zabkar

--
Please remove one \'i\' from my address when replying by email.

Hmmmm. You might be right there Franc. I have downloaded so many different versions and schematic sets, that I seem to have missed looking closely enough at a couple of the pages. I will have to get the amp back on the bench again tomorrow, and compare the schematic and layout I have just found, to what is actually in there. In the meantime, could I trouble you to post the URL of the manual you are looking at, just to make sure that we are both looking at the same one.

Thanks Arfa

On Tue, 12 May 2009 02:39:03 +0100, "Arfa Daily" put finger to keyboard and composed:

It's the same one Don found:

- Franc Zabkar

--
Please remove one \'i\' from my address when replying by email.

Ah yes, OK. We are in fact looking at the same one. Unfortunately, what is shown in there on pages 11 and 14, is still nothing like what is actually in the unit itself. For instance, IC7 on that diagram, is a PIC. On the 'real thing', IC7 is an 8 pin SIL opamp. And many other differences. I am beginning to think that I am not going to get the correct diagram for this. I think as a next move, I will take the board out, and see if I can follow the tracking from where I know that there is signal present, to see if I can arrive at the first opamp, and figure what is going on. Beyond that, I'm not going to waste a lot more time on it. As I'm sure you know yourself, there comes a point when you have to make a decision based on commercial logic, rather than a desire to be satisfied by fixing everything that gets thrown under your gaze ... :-\\

Arfa

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I did some more searching a couple of nights ago and found these links that might be useful, perhaps not so much for this thread.

This one has a number of product schematics for a range of companies.

It seems that AM is still a busy brand....

I also found these two comments in an old repair forum: "On the Australian Monitor site are a number of schematics, but not the KA-1500 - I emailed them and told them that I am a repairer and got the service manual in pdf form immediately - thanks AM."

"Unlike the other guy in this thread i haven´t had the luck of recieving a schematic for the AM1200 even though i´ve written Australian Monitor a mail for it."

Maybe a message to their tech support about variants of the model may elicit a useful response?

Don

Worth a try perhaps. I'll see if I can get a number off the board, and see if they are able (willing?) to supply the appropriate schematic. Thanks all for the efforts anyway.

Arfa

Ha ! A result ! I flashed the service manager an e-mail, and back came three zip archives containing everything they have. I have now found the correct schematic for the mixer board (I think ... ) Unfortunately, there doesn't seem to be a layout diagram anywhere for this particular board, but I guess you can't have it all ways, and at least I have a schematic now. So if anyone else ever needs these diagrams, I have them d;~}

Arfa