TTI PSU EX1810R repair

[themoog]

Hi all (&Dave) been watching the eevblog videos for 4 odd years now, and finally thought i would post a question.. So just joined!

Ive just been given a faulty EX1810R

Doesn't power up, you get the familiar tick-tick of a switch mode trying to start. TTI supplies are good supplies so worth fixing. The primary side seems ok, and the mains input fuse hasn't blown. With the exception of the incoming mains reservoir cap which is fine, there are only about 7 other electrolytics, so i've ordered some low ESR replacements and we can give that a whirl first by changing them. I did check a couple out of circuit and my ESR meter shows them to be leaky... but its always hit and miss. All the main rectifier diodes seem ok and are not short or open....a quick poke at a few key resistors didn't show up much either

.. any thoughts from the forum?

Has anyone got a service manual or diagram too?

Thanks in advance all

Neil

[KJDS]

If you send TTi a nice email then they'll usually send a schematic

[themoog]

Ok cool have done, fingers crossed!

[orbiter]

If these are similar in their PCB design to the QL355 series. Check the upper board for small 1A PCB fuses, as I know the QL355T etc have 6 fuses in all on their PCB's (3 fuses per PCB.) 

[themoog]

Thanks

+ Obiter, this is pretty much a  single board for the supply I have... I have already checked what look like all the fusible links.

+ KJDS, Thanks and they supplied one, although not quite exactly the same board, the silkscreen doesn't match, but if you trace the CCT through you sort of can see the similarities.

Here a link to the service manual they sent -

https://dl.dropboxusercontent.com/u/8285197/EX1810R%20Service%20Manual.pdf

Alas a full re-cap has failed to yield results.

On the plus side, at least i’ve swapped out the "wun hung lowe” brand(s) with low ESR Panasonic caps for the future when it does work.

So, im going to focus on the first part of the circuit….

Im a bit suspect about the “zener?” diode D56, when measuring across this with a DVM it alternates in time with the audible tick.

https://www.dropbox.com/s/9q1drgvk0ecykeg/EX1810R_Service_Manual_pdf__page_24_of_26_.jpg?dl=0

Thoughts?

Neil

[themoog]

So actually if you look across the DC output terminals of the first main bridge rectifier, its glitching in time with the audible tick there. Right at the front end.

I did take out the bridge rectifier to test it out of cct, I suspect its a load component, but thought I would just check. Unfortunately one of the pins came off, so need to order a new one.. A brief test of the bridge with my DVM suggests its working.

So .. thoughts?

[megajocke]

Ticking suggests the protection circuit is activating or that the primary side low voltage supply could be faulty.

The protection circuit is activated by overcurrent or overvoltage. Do you get any voltage across C33 and C37? As described in the service manual, if the magamp circuit is not working properly the supply will shut down as the voltage rises too high on these capacitors.

Shorted components on the secondary is another possibility that would lead to ticking.

[wraper]

So actually if you look across the DC output terminals of the first main bridge rectifier, its glitching in time with the audible tick there. Right at the front end.

I did take out the bridge rectifier to test it out of cct, I suspect its a load component, but thought I would just check. Unfortunately one of the pins came off, so need to order a new one.. A brief test of the bridge with my DVM suggests its working.

So .. thoughts?

If there was something wrong with rectifier, most likely fuse would blow. Very likely you have some shorted diode on secondary that prevents PSU from starting (D26, D24) or some other short in secondary. Also could be some issue in the part which is powering "PRIMARY CONTROL PCB ASSY".