Dear friend, thank you so much for your patience to answering in my questions and give solves to my problem ! If it will work then please let me donate you some euros... Because otherwise I would have to buy a new device or even a used one...

Because the circuit is a bit difficult for my electronics level finding the voltage sources, and understand if the bad diode is in series or in parallel connection, do you believe a 1N4148 diode (150mA 100V) could make the job ?...

Why in paraller ? Between contact 2 and 5 (which is the 48Volt relay) is the bad diode and as far I can understand it is in series, because the one end starts from contact 2 and the other end (of diode) terminates on the contact 5. Is that wrong ?
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Yeap, that's the bad guy !...

Sorry for the previous draw it was wrong !

Here the right one :

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Thank you for your answer Iotas, but here are in series not in parallel and that's why I can't really understand what type of diode need to replace..

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Well nothing special about me , trying some repairs of mine, not for day living job. In the past I was using commodore Amiga 500 & A1200 a lot and like to repairing old and new stuff as well.. Also I am new in the field of music orchestration DAW...

Hello and happy new year ,

my Analog Combustion Machine Honeywell gone bad and I don't know what type of diode is utilized.

There is no mark around the body of the diode. The Schematics are general referred only, without any electronics components and values.

The two contacts (2),(5) of the Relay Coil need 48 Volts DC to begin operating. Between these two contacts in series is the bad diode and near of contact (5) is the bad pnp (bc856b) Transistor that can be easily replaced.

I have made a diagram of the PCB and some measurements along some...