Avalon 747 technical schematic

[salurdigat]

Hi. Anyone has the Avalon 747 schematic document? The valves section in not working
Sending it to the manufacturer from the country where I live and receiving it again would be very expensive due to the fees
Thanks in advice.

 

[gyraf]

We have never (yet) seen such a schematic in the wild. Your best chance is probably to ask the company.

 

[noizetoys]

Avalon's tech guy is a friend of mine. He said they never release their schematics to customers.

He recommended you email '[email protected]'.

Without knowing the specifics he just had a list of things to check:

• Bad Tube?
• Bad cap (check for puffy caps)?
• Bad rectifier that took out a supply voltage?
• Molex connector on the secondary side of the main transformer. Look to see if the red/black pins are discolored. If so, hard wire the connector and replace the last, large bridge rectifier

 

[pucho812]

Avalon's tech guy is a friend of mine. He said they never release their schematics to customers.

He recommended you email '[email protected]'.

Without knowing the specifics he just had a list of things to check:

• Bad Tube?
• Bad cap (check for puffy caps)?
• Bad rectifier that took out a supply voltage?
• Molex connector on the secondary side of the main transformer. Look to see if the red/black pins are discolored. If so, hard wire the connector and replace the last, large bridge rectifier

Audio rehab is their u.s. authorized service center, might be better to send it elsewhere. Especially if you are in Europe. As for schematics the units are pretty easy to work in without them, you just have to think like Avalon.

if the tube section is not working, there are very few things it could be. I have test notes I can get you. Assuming the tubes are ok the usual suspect is the psu. It’s rare that it is anything else. The good news is it shares a supply with the 737. I would bet a failed bridge rectifier, kbu6d on the 6.3v rail and a shorted c23 capacitor. I forget the value off hand. That is a common failure point. When replacing the bridge rectifier, make sure to cut it out so that you have individual pins to desolder, otherwise you risk pcb damage. This is because the kbu6d absorbed a ton of heat making it hard to remove as 1 piece.

 

[salurdigat]

Thanks to everyone for the help.
The valves are new ones.
I´lll write to Greg for support to repair here in Brazil if possible.

 

[Memo Solis]

Check +6V on power Supply usualy its working very very hot remplace it an be sure use new mica too.

 

[Memo Solis]

+6V regulator, TO-220 style

 

[pucho812]

Any update on this?

 

[Memo Solis]

Try to use ON Semi brand

 

[pierre245]

Hi... No documentation about 747? I have a unit , with no Sound out After the soft start get on.... The diode looks a bit Dim... I guess a PSU problem... Si looking for PSU schematics to measure rails. Thanks

 

[pucho812]

Hi... No documentation about 747? I have a unit , with no Sound out After the soft start get on.... The diode looks a bit Dim... I guess a PSU problem... Si looking for PSU schematics to measure rails. Thanks

The unit uses the exact same PSU as there 737. I have posted here before, pinouts of the PSU and other things to test and measure for the 737, I have the same for the 747. Even if you are using the solid state path and not the tube path, the PSU still needs to be in order for the unit to pass audio. PSI should have +/-32VDC, B+ of around 180-185, 12VDC, for logic and 6VDC for the 6922 tubes, I can help you if you ask questions. I can point you where to measure to confirm you have the correct voltages.

 

[chrispbass]

Hi... No documentation about 747? I have a unit , with no Sound out After the soft start get on.... The diode looks a bit Dim... I guess a PSU problem... Si looking for PSU schematics to measure rails. Thanks

Lots of info on here if you search.

Pucho helped guide me (and many others) when fixing my friends 737. Cost about £10 English pounds in parts. Good luck…you can do it

 

[pucho812]

Lots of info on here if you search.

Pucho helped guide me (and many others) when fixing my friends 737. Cost about £10 English pounds in parts. Good luck…you can do it

10 quid? was that all. Nicely done mate.

 

[pierre245]

Hello there… Thanks guy, you are so reactive… I try to measure things in between time. I just take the measurements in the output of the PSU (without load off course) I disconnect PSU from the PATH , I take measurements . I find that : (Im in a 240V entry AC).
I find there :
- a line of 6.3 V
- a line of 12.1 V
- two line like -35V and 35V
- And a last one 100 V.

The 747 looks ok like 45 seconds, I see compression modulation, all buttons looks OK etc… but when the start get on, machine looks off.

 

[pierre245]

The unit uses the exact same PSU as there 737. I have posted here before, pinouts of the PSU and other things to test and measure for the 737, I have the same for the 747. Even if you are using the solid state path and not the tube path, the PSU still needs to be in order for the unit to pass audio. PSI should have +/-32VDC, B+ of around 180-185, 12VDC, for logic and 6VDC for the 6922 tubes, I can help you if you ask questions. I can point you where to measure to confirm you have the correct voltages.

Hi Pucho, thanks to give that information. It looks I have a PSU problem so … on the 180 V line. I only have 100 V… So … I have to recap that line I guess ?

 

[chrispbass]

10 quid? was that all. Nicely done mate.

Not far off. New bridge and cap. Replaced the reg (just In case) although prob fine. Molex plug/shell and crimps and a bit of time in my lab which is generally a joyous occasion.
Had considered ditching the plug and hard wiring (prob better tbf) but still enough life In the pcb to keep ‘it stock’, but if it ever craps out again then an option

 

[pucho812]

Hi Pucho, thanks to give that information. It looks I have a PSU problem so … on the 180 V line. I only have 100 V… So … I have to recap that line I guess ?

That would be a good first step

 

[pierre245]

I find your post about the measurement of the 737. So that confirm the fact B+ line tolerance is only 5V. So with only 100V , the PSU isn’t correct. I guess that why the 747 cant correctly boot on.

 

[pierre245]

I see three bigs caps on that line, 2 2200uf sur 63 V and 47uf on 250V. Start with that three tomorrow ! Thanks

 

[pucho812]

I find your post about the measurement of the 737. So that confirm the fact B+ line tolerance is only 5V. So with only 100V , the PSU isn’t correct. I guess that why the 747 cant correctly boot on.

Did you find the 6 V and 12 V as well as the bipolar 32 V?