Re: Challenging 2465 PS repair


satbeginner
 

Hi all,

here an update on the repair progress : (not so much)

My previous conclusion that the Primary switcher was now repaired might not be true after all... :-(

Since many things are/were broken in this Power Supply, I have to work my way back from almost the end of the troubleshooting flowchart,
so the test with the Primary Load as first, and yes, that test work perfectly on both Switchers, except for the ripple measurement, but again, I think it has to be measured across the capacitor in the test-load.

However, the second step towards the beginning is to leave the secondary transformer connected (so with W1060 back in place) and all the combs between A2 and A3 removed, to just test the 5VD created on the A3 PCB using the 2 Ohm resistor(s).
With all combs removed the feedback from the second regulator board is missing in this situation, so the 5VD is solely depending on the feedback coming from primary Pin-7 of transformer T1060.

Here is when the first major difference comes in: (there are two)
1. with just one 2Ohm resistor as load on the 5VD the working switcher gives out a nice 5.01V, but the one I am repairing settles at 4.28V.
I will test further, but maybe because of the burn damage earlier, some of the resistors around the switcher IC U1030 (TL594) have changed value, so the feedback on pin 1 and 2 of the TL594 might be off.

2. The second issue is, that the switcher will not always run. When I increase the Line voltage it will start around 175-180VAC, but it will stop when at 230VAC.
I found it is the Current Limit circuit around Q1040 is causing this, although this does NOT happen during the first test, using the Primary Load only.
For testing purposes I temporarily disconnected R1042, so at the moment there is no current limit.

My thought is that maybe also T1060 has a problem, but to investigate further I am in the process of disconnecting all the diodes from the secondary windings, and only leave dual diode CR1110 in place for the 5VD and the load.

Here in Spain the temperatures are now approaching 40 C, so the hobby intensity is stepped down a bit, to be continued later this week.

Formula-1 this afternoon :-)

To be continued, un saludo,

Leo

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