Hi - my first post so please be gentle! 😆
A very specific question: can anyone help me identify component from a 1980s-era Meridian Component Amplifier (MCA) Pre-amp power supply module, placed in the circuit between the generic 18v AC input and en route to an LM7805 regulator.
All indications are it’s a diode performing its role in the half-wave rectifier circuit. Made by Motorola, its designator is:
C
24
408
My Peak meter doesn’t recognise it, or it’s gone bad. I cannot find reference to it anywhere on t’internet (including old Motorola ‘equivalency’ documents that crop up) so have no idea what to replace it with!
Can anyone point me in the right direction please?
A very specific question: can anyone help me identify component from a 1980s-era Meridian Component Amplifier (MCA) Pre-amp power supply module, placed in the circuit between the generic 18v AC input and en route to an LM7805 regulator.
All indications are it’s a diode performing its role in the half-wave rectifier circuit. Made by Motorola, its designator is:
C
24
408
My Peak meter doesn’t recognise it, or it’s gone bad. I cannot find reference to it anywhere on t’internet (including old Motorola ‘equivalency’ documents that crop up) so have no idea what to replace it with!
Can anyone point me in the right direction please?
Thanks fellas, that’s great corroboration.
I get the feeling from looking at some of the other components that the Meridian engineers simply used stuff they had to hand - the other 2 diodes for the main positive and negative rails are BA159s rated at 1000v when scarcely 25 volts comes off the transformer secondary! Would there be a special need for a zener to be used for the additional 5v feed?
I get the feeling from looking at some of the other components that the Meridian engineers simply used stuff they had to hand - the other 2 diodes for the main positive and negative rails are BA159s rated at 1000v when scarcely 25 volts comes off the transformer secondary! Would there be a special need for a zener to be used for the additional 5v feed?
@Mark Tillotson - the only markings on the devices are the Motorola ‘M’ logo, then C, 24, and 408 on three separate ‘lines’.
Can you draw out what the circuit looks like? There may or may not be a reason for it to be a zener. Is it just a half wave rectifier? Some sort of OVP clamp? Perhaps dropping excess voltage before hitting the 7805?
Forget "smart" meters, what does a Multimeter show in the diode scale, both ways?
To test its Zenerness, get a >40V supply, connect it to mystery component through a 10k resistor, measure voltage across it.
Inverse it and repeat.
What do you get?
Glucose and oxygen powered wet brains can very well replace electrons and sand microprocessors if running the proper software.
To test its Zenerness, get a >40V supply, connect it to mystery component through a 10k resistor, measure voltage across it.
Inverse it and repeat.
What do you get?
Glucose and oxygen powered wet brains can very well replace electrons and sand microprocessors if running the proper software.
I’m ’reverse engineering’ a schematic from inspecting the circuit board itself - it’s not quite ready but I think I can put up the detail pertaining to the AC input. I’ll try and post it now…
It seems to be a voltage clamp to prevent the 7805 being fried, if the current draw is so low to allow voltage to be dropped across R1, so 24V would make sense.
As for reuse of over-spec diodes, sometimes it's actually cheaper to bulk buy one type of device 🙂
Yes, it’s a voltage clamp. Maybe use a 1 watt instead to prevent it from frying again? 1N4742’s are cheap.
I bet you do.
All do.
Please post a multimeter scale picture so anybody here can point at it.
Guys - can’t thank you enough for your help with this. Really appreciate it 😃👍🏼