Hi,

my Avant 100 Hz VTR, Model 83/00 from 1996, went out with a bang, in a quite literal sense. Now when I plug it in I hear some repeating hissing sound as if it's trying to start, but nothing happens. Not even the LED will light and I can't get any reaction out of it.

I suspect it's a failure in the switching power supply, and my first step would be to replace the electrolytics, but a schematic would be a big help. I couldn't find it in the manual section, as it says I have no permission.

This is my only B&O device, and I got it only two days ago, so can anyone tell me whether the schematic is available for download here before I upgrade my membership?

Any other suggestions, as far as the failure is concerned, are of course highly appreciated... I have no experience with B&O so far and I'd really like to get this fine TV going again...

Thanks and regards,
Leo

I'll need to check when I get home, but I suspect that most of these manuals have no useful schematics in. The vey first Avant manual does but I will check the type number and get back to you.

Maybe you can use this one Service manuals

Thanks Tillquist, this looks great, if a little complex I have no idea how well it matches the 83/00, but I'll try to find out soon!

Greetings, Leo

We have that one - without Beocollectors written all over it! - but it does not have a full schematic. I do have an early one with schematics but It is an earlier type. 810X

My advice would be not to just replace C's before you establish if one is faulty, rather first find the cause.

It might well be something like a short diode and you'd be replacing C's for nothing...:)

Without schematics but with no led i'd start with ohm meter, check the secondary side of the power supply for a short (might be in the power supply itself but also in the circuitry connected).

Hi Peter,

how similar are the 810x and 83xx models? Do you think the schematic would be helpful?

Kind regards, Leo

Hi ipaul,

thanks for the advice. After checking the power supply I intend to disconnect the attached PCBs to see whether it starts up. Do you think this would work or does the SMPS require some sort of minimum load?

Kind regards, Leo

OK, I have just opened the TV and noticed that it's not as easy as that. The SMPS and the rest are mostly connected by soldered wires.

I guess I'll just start with the power supply then...

I am afraid I cannot tell you! Personally, I don't feel capable of opening TVs - too much voltage for me! Maybe a more expert person can comment.

The 81xx is the old 50Hz model, with technology quite like the MX and the 83xx is 100Hz.

Some things are somewhat similar but component numbers etc are different so the 81xx manual won't be more than a bit of guide to roughly know the setup of any avant...

The smps will probably not work standalone but you could load it with a light bulb of about 40 watts on the +135 V (or 155 v something like that), but i'm not completely sure that works with the avant smps (but won't harm).

The flatcables should be connectors on 1 end and fixed on the smps board, just check if the other end of the flatcable is detachable (but there seen to be different versions of this).

In any case: just an ohm measurement on the smps caps can be done anyhow, as a step 1....

I have now checked the SMPS board, but so far there is no conclusive result. I had to unsolder the two flat cables that connect the board to another board (looks like the main processor board), both ends are soldered.

The schematics for the 81xx and my model seem to be quite similar. There are some differences in the components (my power driver FET seems to be a more recent model, for example), but the numbering seems to be almost identical. Too bad there is just a block schematic and not a detailed one.

I've measured all discrete semiconductors and found no faults so far, except the MOS driver (an STH7NA90FI) which seems to be damaged. The Drain-Source diode at first behaved like a capacitor under the DMM, then after shortening the leads it tested normal. That puzzled me much. The component is not readily available any more but I found a guy who will send me some and I'll change it for a test.

The SMPS behaviour is strange, it tries to start but there is no voltage on most of the secondary circuits, except one which measures about 11V. The feedback circuit has no power or very little, say 0.5V, and there is no signal at the optocouplers. TR12's emitter, that's the Q responsible for overload protection on the primary side, goes up and down with a frequency of about 1 Hz. There is some very high frequency ringing on the coil, but I can't trigger the signal correctly on my oscilloscope as it's only intermittent. The frequency also seems too high for normal SMPS operation. The caps on primary and secondary seem ok.

My best bet currently is the power MOSFET. It's too bad that there is no detailed schematic; should, for example, an SMD transistor or diode be blown I wouldn't even know the type or polarity. There are also no voltages labeled on the PCB so it's a lot of guesswork, especially as this SMPS is quite complex with all the PFC and protection stuff.

If anybody has additional ideas, please let me know. Kind regards, Leo