Hi,
this question relates to the PSU fitted in one module of my Memotech Videowall system. The original question was raised on Facebook when I could not identify the model number of the PSU and I was lookinig for a suitable replacement. I have now identified the model number (Skynet SNP-3031), there is a replacement available from Skynet, the SNP-9031. Whilst I will try to source one as replacement, I also want to see if the faulty PSU is repairable, so have raised this thread to capture the most relevant information from the Facebook page and ask for additional support from the Group here.
Input specifications: 120V-1A, 240V-0.5A, 50/60Hz.
Output specifications; V1: +5V/2A, V2: +12V/1.5A, V3: -12V/.3A
Mark (Kinsey) had identified the control IC (a UC3842) from the photo on the Facebook page, and made some suggestions, including :-
" Have you been brave enough to do any tests on the PSU with a meter? It could be as simple as some defective electrolytic capacitors (mains filter, or output filter), a faulty start-up capacitor or resistor, or a faulty opto-isolater. I assume you have checked the fuse? If the fuse is okay, it is likely that the input bridge rectifier diodes are okay (they normally take out the fuse when they die)."
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Current Status - bad choice of words - the output is of course, currently 0
- the status of the fault finding is as below
When I initially inspected the PSU, all of the components looked OK physically, apart from the mains input filter capacitor - I could not decide whether it had leaked some electrolyte, or whether it was fixed to the PCB with an adhesive of some sort. Subsequently, I removed the capacitor and found that it had actualy leaked from the vent plug at the bottom, although a close look at the top of the capacitor suggests that it is slightly "bowed" - possibly due to the lid bulging, under the plastic cover.
I have replaced the capacitor and still have the same problem, I guess that the failing capacitor has taken out some other component(s) on the board. I'd appreciate some additional pointers as to where the problem might be and whether I can do any additional checks before replacing components on a "trial & error" basis.
I am not getting any voltages on the secondary side of the transformer, so it's probably a fault on the input side of the board, rather than the output/regulation side.
I can't find a schematic on the web, but Mark indetified the control IC as a UC3842, and I have identified the input rectifier as a SN1B. The rectifier seems to be working, with ~340VDC on the output.
regards
Dave
Videowall PSU - Transfered here from Facebook Group
Videowall PSU - Transfered here from Facebook Group
- Attachments
-
- Reflex Controller PSU Photo
- Daves_VW_Decoder4_psu_240.jpg (9.37 KiB) Viewed 10802 times
Re: Videowall PSU - Transfered here from Facebook Group
Voltages at each side of the main transformer are odd - to me anyway.....
1. On the mains side, between the windings and the DC common, I get
+190, +190, -134, -134
2. On the maiins side, between the windings and what looks like an AC common. I get
+145, +145, -60, -60
3. On the LV side, between the windings and the DC common, I get
0V, 0V, 0V, 0V
4. On the LV side, between the windings and the AC common, I get
+24V, +24V, +24V, +24V
(All voltages are DC)
Given 3., does it look like the transformer is u/s ?
regards
Dave
1. On the mains side, between the windings and the DC common, I get
+190, +190, -134, -134
2. On the maiins side, between the windings and what looks like an AC common. I get
+145, +145, -60, -60
3. On the LV side, between the windings and the DC common, I get
0V, 0V, 0V, 0V
4. On the LV side, between the windings and the AC common, I get
+24V, +24V, +24V, +24V
(All voltages are DC)
Given 3., does it look like the transformer is u/s ?
regards
Dave
Re: Videowall PSU - Transfered here from Facebook Group
Hi Folks
no suggestions?
regards
Dave
no suggestions?
regards
Dave
Re: Videowall PSU - Transfered here from Facebook Group
It is possible, but unlikely that the transformer has gone.
Much more likely is a fault in the control and feedback system.
I will be able to suggest more once I have looked in detail at the pictures and compared the circuitry/wiring to the example circuit in the second of the data sheets that I linked to on the Facebook page.
I have a number of other projects that I am working on, this is #4 in the electronics queue (not all MTX related before you get too excited plus the gardening, DIY/repairs and other outside related activates)...
Mark
Much more likely is a fault in the control and feedback system.
I will be able to suggest more once I have looked in detail at the pictures and compared the circuitry/wiring to the example circuit in the second of the data sheets that I linked to on the Facebook page.
I have a number of other projects that I am working on, this is #4 in the electronics queue (not all MTX related before you get too excited plus the gardening, DIY/repairs and other outside related activates)...
Mark
Standby alert
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer in Somerset later in the year
Not as many MTXs as Dave!
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer in Somerset later in the year
Not as many MTXs as Dave!
Re: Videowall PSU - Transfered here from Facebook Group
Thanks Mark,
I'd appreciate your input when you get some time
regards
Dave
I'd appreciate your input when you get some time
regards
Dave
Re: Videowall PSU - Transfered here from Facebook Group
I'm sure that you will be glad to know that this is the next reverse engineering project that I am starting on
@ Dave, It would be helpful if you could list the marked values of the components please.
Mark
@ Dave, It would be helpful if you could list the marked values of the components please.
Mark
Standby alert
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer in Somerset later in the year
Not as many MTXs as Dave!
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer in Somerset later in the year
Not as many MTXs as Dave!
Re: Videowall PSU - Transfered here from Facebook Group
Hi Mark,
great! - thanks a lot, I will read off the components later today,
regards
Dave
great! - thanks a lot, I will read off the components later today,
regards
Dave
Re: Videowall PSU - Transfered here from Facebook Group
Bottom of PCB picture edited and converted to a monochrome image...
Mark
Mark
- Attachments
-
- Daves_VW_Decoder4_psu_ss_edit B&W-p.png (184.82 KiB) Viewed 10742 times
Standby alert
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer in Somerset later in the year
Not as many MTXs as Dave!
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer in Somerset later in the year
Not as many MTXs as Dave!
Re: Videowall PSU - Transfered here from Facebook Group
Hi Mark,
sorry for the delay - I have most of the components now I think.....
R1 = 5R
C1 = 0.1uF
C7 = 100uF
R16 = 330R
DB = S1NB
C7= 100uF 400V
C10 = marked 471 2KV - 47uF?
C17 = 470= uF 25V
D6 = Illegible
C19 = 330 uF 25V
SCR1 = masked by holder
C18 = 1000 uF 10V
C2x = 120 uF 25V
C20 = 330 uF 25V
R19 = 10R
DZ1 = ?
R23 = 4.7R?
C24 = 103Z 500V
C3 = Z5U 103M 1KV
C2 = ?
IC2 = TL431
R8 = 10K
R9 = 500R
R11 = 5.1K
R10 = 330R
R5 = 15R
R2 = 150K
C8 = 22uF 25V
R7 = 100R
R3 = 0.56R
R6 = 5.1K
R13 = 4.3K
C21 = 120 uF 25V
R21 = 390R
R22 = 390R
R24 = 4.1R
regards
Dave
sorry for the delay - I have most of the components now I think.....
R1 = 5R
C1 = 0.1uF
C7 = 100uF
R16 = 330R
DB = S1NB
C7= 100uF 400V
C10 = marked 471 2KV - 47uF?
C17 = 470= uF 25V
D6 = Illegible
C19 = 330 uF 25V
SCR1 = masked by holder
C18 = 1000 uF 10V
C2x = 120 uF 25V
C20 = 330 uF 25V
R19 = 10R
DZ1 = ?
R23 = 4.7R?
C24 = 103Z 500V
C3 = Z5U 103M 1KV
C2 = ?
IC2 = TL431
R8 = 10K
R9 = 500R
R11 = 5.1K
R10 = 330R
R5 = 15R
R2 = 150K
C8 = 22uF 25V
R7 = 100R
R3 = 0.56R
R6 = 5.1K
R13 = 4.3K
C21 = 120 uF 25V
R21 = 390R
R22 = 390R
R24 = 4.1R
regards
Dave