Re: Challenging 2465 PS repair


Jean-Paul
 

Leo: Very fine work....haved designed SMPS since 1970s...and debugged 246x PSU....

1/ Virtually all SMPS have UVLO and OVLO = undervoltage and overvoltage lockout, the input V is sensed and switching inhibited till the DC bus is in range.

I have never had issues in using a variac to test SMPS. Use of Variac reduces chances of blowups if a part has a short.

2/ These are indeed complex designs but very reliable. The flowchart and debug procedures in the TEK serv manual are excellent.

3/ Blow switch transistors will often be symptoms of other issues and the driver IC or transistors in the switch circuit are at risk.

4/ There was discussion of the proper loads and connectors for dummy testing..long ago.

5/ I have indeed used a DC bus from a variable lab supply to test these, but this is rather dangerous and the lab supply current limit will not guarantee safety if the SMPS has faults!

6/ Besides RIFA X/Y line caps, all lytics (ELCO) can be at risk, especially in the LV rewct section. The HV bus caps (360V bus) seldom fail.

7/ The schematics PCB layout have a reversal of two caps in the LV rect section, that can result in problems when recapping.

8/ The rectifiers and switch transistors are easy to check in circuit.

Hope this note is of use,

Bon Chance,

Jon

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