Hameg Spectrum Analyzer Power Supply -- Unidentifed Diode

[rodd]

Hi folks,
I started to repair a Hameg 5005 Spectrum Analyzer which has no trace on the screen.
So I started with the power supply.
Up to now, I fdiex the +12V replacing a TL082 op amp and a TL431 regulator.
All low voltages are ok now, but I have a problem in the HV.
When I start to follow the schematics I fund D1557 (smd type) marked with a *.
I looked everywhere in the other sheets od the manual and there is no mention to it.
Can anybody figure out which diode is it?
It seems to be a zenner diode, so what voltage?
Thank you in advance for the help.
Roger

[Dachpappe]

Well I also didn't find anything where the exact value of the diode is mentioned.
But by how the diode is placed in the circuit it should be a low zener-value.
It's parallel to the Base-Emitter section of T1553 which according to the datasheet has a max voltage of 5 volts. So it's probably between 0,7 - 5,0V. Have you checked the zener if it's really dead?

[bktemp]

A zener diode actially doen't make sense, because it is in parallel with the base-emitter diode, therefore the voltage never goes higher than ~0.7V. In reverse direction it acts as a normal diode limiting the reverse voltage.
I have a similiar power supply (PS5011) here, the diode is unpopulated. Maybe that's why the manual doesn't mention a part number.
If you want to place a diode, a 1N4148 should do the job.

[barroweer]

Hello. I have such appliance (may be Hameg 5510) which i was got like a gift recently but almost completely broken down. Fortunately it has a few boards nearly intact, the power supply among them. I've made some photos of rear and attach link on the service manual  of proper quality (http://www.frankshospitalworkshop.com/equipment/documents/workshop_equipment/manuals/Hameg%20HM5010-5011%20Spectrum%20Analyzer%20-%20Service%20manual.pdf). And, interestingly, on my board this diode wasn't placed at all (see pages 37 and 50 in service manual).  Does your board have this one?