Neil, no problem. You seem to have used a slightly different email address to
the one I’ve seen before. The list is very sensitive to this!
Scanning the manual again, I note another couple of interesting facts:
1. the PSU can be setup for 110v or 230v - might be worth checking you have the
right setup, it’s hard-wired inside!
2. the manual indicates that the voltage regulation sensing is coupled on the
front panel (I might have misread), again, could be worth checking that the
necessary straps or links are in place.
On 29 Aug 2015, at 18:09, Neil Bernard <neil@xxxxxxxxxxx> wrote:
Thanks mark for reviewing see inline below…. if you ever fancy helping my out
in the physical world It would be much appreciated. My electronics is very
rusty (haven't done any real electronics in 10+yrs)
Anyway thanks again! I would love to get this supply running!
On 29 Aug 2015, at 16:16, Mark Kent <mark.antony.kent@xxxxxxxxx
<mailto:mark.antony.kent@xxxxxxxxx>> wrote:
Neil, you, perhaps you should subscribe the email address to the mailing
list.
- No no problems ill have a look at that, perhaps thats why it wasn't working.
Main point for consideration:
The operation of the internal protection circuit is described in the section
‘main output’. Here, the voltage across c33/c37 triggers a zener, which
drives an opto-isolator, which drives Q22/23 as a bistable latch, causing
tripping, which is what you’re describing.
Good point, prove the fault
Can you get a scope onto the capacitors and validate the voltage?
Will do
Similarly, this latch is also driven from excessive Mosfet output current,
sensed by the 0.33Ohm R16. Nasty causes are the mosfets, any of the diodes
going short or ‘zener’, perhaps a shorted turn on the output transformer.
0.33Ohm is ok i’ve tested it one ended, mosfets seem ok and are switching,
see attached for an example
<DS1Z_QuickPrint2.png>
Good point
The fact the the PSU is being driven into self-protection is quite a good
sign, as it indicates that most of it is working, including the
oscillator/PWM parts and out to the driver stage.
Quick observations:
0. Do you know what caused the failure? This is often a useful guide to
where to look and consider.
Unfortunately no, I acquired it in this state
1. things which go wrong are usually those which get hot. Power devices in
the SMPSU are a good place to look, so the power mosfets must be considered
suspect.
Mosfets seem ok so far
2. the auxiliary power supplies are critical to operation, so check the
volts are present and correct.
Will do, swapped out a 7805CV as I had a spare, no luck
3. close visual inspection - do any parts of the board look heat damaged?
Resistors can go well off value when over heated.
Nothing obvious
4. An electrolytics which are bulging must also be considered suspect.
Swapped out all electrolytics already, there were only 7.. Swapped with good
quality panasonic, Low ESR versions.
5. The control electronics are very well described in the text; if you can
isolate them from the rest of the circuit in blocks, you can run them up on
independent supplies and validate that they’re working as expected.
Will do
I’d start with the power devices, though…
Thanks Mark.. Lots to try
On 28 Aug 2015, at 20:28, keithlbird@xxxxxxx <mailto:keithlbird@xxxxxxx>
(Redacted sender "keithlbird@xxxxxxx <mailto:keithlbird@xxxxxxx>" for
DMARC) <dmarc-noreply@xxxxxxxxxxxxx <mailto:dmarc-noreply@xxxxxxxxxxxxx>>
wrote:
Dear club colleagues, I'm forwarding the attached on behalf of Neil, if you
have feedback or can help Neil please contact him directly at
neil@xxxxxxxxxxx <mailto:neil@xxxxxxxxxxx>
73 Keith
-----Original Message-----
From: Neil Bernard <neil@xxxxxxxxxxx <mailto:neil@xxxxxxxxxxx>>
To: keithlbird <keithlbird@xxxxxxx <mailto:keithlbird@xxxxxxx>>
Sent: Fri, 28 Aug 2015 18:16
Subject: Help required - Bench PSU Help (TTi 1810R)
*******
Hi WKARS team
Bench PSU Help (TTi 1810R)
Ive been donated a very fine 18V 10A Bench supply, if I can fix it.
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 ok.. 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..
Ive had a poke around a few key voltages and I do have a service manual
(https://www.dropbox.com/s/txkn4byzkdsvfiw/EX1810R%20Service%20Manual.pdf?dl=0
<https://www.dropbox.com/s/txkn4byzkdsvfiw/EX1810R%20Service%20Manual.pdf?dl=0>)
althoung the silk screen doesn't always match.
Getting stuck now, any thoughts or help… much appreciated.
Neil
M6DWU
neil@xxxxxxxxxxx <mailto:neil@xxxxxxxxxxx>
