Allen and Heath ZED 22FX schematic

[blindboybenton]

Hi all

Allen and Heath ZED 22FX schematic required or if you know the another model that uses the same PSU.

Burnt out components in the switchmode psu


many thanks and have a good day
BBB

[black bunny]

Howdy folks. Does anyone have a Zed 22 schematic? I have a faulty Zed 22 on my bench, the complaint being that the 48 volt phantom supply stopped working.

The problem seems to be R35, located beside the Phantom Power switch on the motherboard, which is burnt and reads open circuit. Can anyone tell me the value of R35?

Thanks and praises.

[blindboybenton]

hi I have checked my schematics, I have none for this or model.
should be fairly easy to sort out , if no info is forth coming

BBB

[vintagekiki]

Only

https://elektrotanya.com/allen_heath_zed_series_psu_sch.pdf/download.html

https://elektrotanya.com/showresult?what=allen heath

http://music-electronics-forum.com/t38177/

As an idea

https://www.youtube.com/results?search_query=Allen+%26+Heath+ZED+24+Repair.

https://www.allen-heath.com/key-series/zed-series/

https://www.allen-heath.com/media/ML4000-SERVICE-MANUAL.pdf

[black bunny]

Thanks for your help BBB and vintagekiki. The actual 48 volt supply was good, so the problem turned out to be in the feed to the 16 mic preamps, just after the Phantom power switch.
Multiplying the maximum Phantom power current draw of 15 mA for each mic input x 16 channels gave just under 250mA total current draw after the switch, in a worst case scenario with all mic channels drawing Phantom power.

Since R35 is in series with the 48v feed to all the mic inputs, I figured R35 would most likely be a fusible link or very low value fusible resistor. Removed scorched R35, cleaned up the board, check the mic inputs for shorted electro capacitors and found none.
Fitted a 1/4 watt FR where R35 used to be and all is now good - everything running happily. Hopefully this might help someone else with a similar problem sometime.

[black bunny]

Thanks for your help BBB and vintagekiki. The 48 volt phantom supply was clean and stable, so I thought the problem was probably on the load side of the phantom power switch.
I checked the 16 mic inputs for shorted electro caps or transistors and found no problems.

I calculated the maximum current draw from the 48v supply in the worst case scenario, with all 16 mic preamps drawing 15 mA each, for a total current draw of around 250mA / 0.25A.
Since R35 is in series with the load side of the phantom power switch I figured that it was probably a fusible link or low value resistor. Fitted a 1 ohm 1/4 watt resistor where R35 had been and bingo - everything works.

Hopefully my little win might help someone fix a similar problem.