Hi Syntaur People.
While repairing my ASR10 PSU, I decided to replace the two tiny Zener Diodes nearby the two transistors and the heatsink.
While cutting them from the board to get their voltage, one popped out and is missing in action.
Can’t find any diagram for ASR10 PSU, so here are my questions:
-
The diode that remains is a 1N5255B 28v 500mW
What are the specs of the other one ? Same ?
-
Can’t find 28v zener diodes, but 27 / 29 or 30 volt are easily avaible. Can I replace the 28v by a 27v without issue ?
Thanks
Peter
hi,
I’ll have to check back for you on that.
By the way the 5v dropout regulators take an absolute beating. They are riveted onto a plate. One of these would not produce 5v under load, it was fine when measured without load.
replace them with TSR 1-2450E Traco
Hi we_robot
Thanks for your answer.
The old Motorola T7805CT were already replaced by new ones but I’ll folow your advice.
Traco seem to be more reliable and less heating.
Regarding the zener, it would be great if you had the specs.
Thank you .
hi,
yes will be back to you. just got my ASR10 rack out and need to open it up and get to that Power board. The rack is very difficult to work on as the power supply is below the mainboard PCB.
As for the Traco - the regulators are not a very efficient way to produce stable 5v. the heatsinking is not adequate either.
As said i’ll get back to you soon.
1 Like
Upping the voltage is a good idea. Our ASR-10 PSU Kit includes these diodes;
8 x 50V 3A ( [DO-201, Axial)
and
2 x 200V 6A (R-6 Axial)
Cheers!
1 Like
Hi
Thanks for your answer.
I’ve already changed theses diodes.
I was asking for the specs of the two tiny zener diodes ( gray metal color ) labeled CR11 and CR12
I’ve lost one of them and the other that remains is a 1N5255B 28v 500mW. Just wanted to make sure they were the same or not.
and if they are identical, I ask myself the following question:
28 v zener diodes like this are not avaible but I can easily buy 27 / 29 / or 30v. What would be your choice?
If I can’t repair that psu I will buy another one from syntaur if avaible.
Thanks
These ones 200v 6A R6 axial ?
Ok then, I’ll try, hope they’ll fit…
Many thanks
Mea Culpa, Misread previously, understand you are not talking about rectifying diodes.
Take note from photo, CR12 is not a designation of the protection diode in question. the CR12 is adjacent regulator. Follow the silkscreen outlines.
Q: What is your reason for wanting to replace this diode?
Unless that diode has failed, there is likely no reason to replace it. You can test it by pulling up one leg from the PCB, and checking it with a multimeter.
This diode is part of the DC side, not used for rectification, under no considerable load, likely does not need replacement.
First of all thank you for all your answers.
To answer your question, I simply wanted to overdo, and as often, the best is the enemy of the good. The voltage of these diodes was not visible. I was in a component store and to see the voltage I had to cut them from the pcb. One of them popped out and was never found. But as they had the same color and the same visible reference, thanks to the one that remains I may deduce that they are both 28v. Now I know it was a mistake to change those components that are not subjected to strong electric loads.
I am not even sure that the power supply is the source of the problems of my ASR 10 which worked very well for two years and suddenly froze ( it continued to play, but no control was possible, it was stuck).
When I turned it back on, all the LEDs were on, and the screen was empty. However, letters , numbers and symbols may appear as indicated in the service manual, but not in the leftmost way.
It worked again on ignition once or twice a few minutes after turning it on cold…and then froze again.
I decided to recap the psu ( never done in thirty years ) and proceed by elimination.
PSU ? Digital board ? Analog Board ? Connectors ? Wait and see…
Thanks again.
