Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Power Supplies and Power Supply Design
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 06-23-2019, 02:27 PM   #1
pdavid
Senior Member
 
Join Date: Jan 2011
My Country: Hungary
Line Voltage: 230V/50Hz
Posts: 186
Default Videoton VT-110, XT clone PSU repair

I was having trouble repairing this unit and while searching for info I came across another Videoton design. It came with the pc case and it was a cheap local sale so I picked it up, out of curiosity.




This one is a full AT size unit that is functional but gave a strange whine/buzzing right from startup. After some poking around it was determined that the noise came from the main transformer. There was also a rattling sound when the unit is rotated or shaked. It turned out that on of the main trafos half core has been cracked and broken. There was no sign of big heat damage anywhere so my guess was that it has sustained some kind of physical shock during shipping or before.
It turned out that other components were also failing so I took the whole unit apart

It looks like a push-pull design. Mirroring the '80s eastern block shortage economy. Whatever parts were available in the market were used for design and production. Max output of this psu is about 150Watts.





It has some EMI filtering.
There are fuses socketed in series both on line and neutral:


It has a decent fan that still spins super smooth:


Inrush current limiter has several holes on it and measures 50-60 ohms. It's blown. It has color coding in the form of three dots:


A foil capacitor was measured open and another 100nf+2x2.5nf X2Y wierdo type was 100-200ohms in one part:



Main capacitors measure not so great and leakage current is high. Some audiophiles might think they look pretty cool though:


The unit has a full bridge rectifier:


Two IRF 740 FETs:


Controlled by SG3526N. Supervisor is SG3543J:



I couldn't take it apart without destroying the original heat transfer/insulator sheets.
These sheets were all brittle and were falling apart:


The main transformer is some high frequency core N27 material. I'm not an expert identyifing transformers so it took me some time until it was revealed
to be EC41 type. My second guess was ETD core:


It's still around and super cheap so I ordered some. The Epcos/TDK part goes by the name B66339G0000X127.


Original main trafo with RC snubber hacked on it:



The main board stripped down a bit:


The secondary current stabilizer is also wound around a EC41 bobbin and N27 core material. It's glued together with some rtv silicone.


Output diodes are schottky types for 5V and 12V rail. -5V is generated by 7905 regulator ic:


There is no real low pass filter with inductors just electrolytic capacitors on the output filtering stage. Old Panasonic, Chemicon and random USSR caps are used. These all test ok.

That's how far a I got now. I'll reassemble the main transformer and also might replace some old parts with matching nos parts. These "vintage" resistors, caps are still shoveled around since so much were made and some are still within specs.
Attached Images
File Type: jpg fet.jpg (164.2 KB, 70 views)
File Type: jpg videoton-data-manager-vt110.jpg (100.5 KB, 71 views)
pdavid is offline   Reply With Quote
Old 06-25-2019, 03:49 PM   #2
pdavid
Senior Member
 
Join Date: Jan 2011
My Country: Hungary
Line Voltage: 230V/50Hz
Posts: 186
Default Re: Videoton VT-110, XT clone PSU repair

Reassambled the main trafo with the new cores:

This time with some silicone too. Hopefully it's going to keep the bobbin and the cores from sliding around.

Got several old electrolytic caps of the same brand but the parameters are kind of crap. These just won't do as replacement. I have to use modern parts.

Also going to use real X2 and Y rated capacitors for the EMI stage.

For the primary bulk these capacitors will be much better then the originals I think:


I want to sacrifice as less authenticity as possible but that might not turn out to be safe enough.
Attached Images
File Type: jpg DSCF6566.jpg (206.4 KB, 55 views)
File Type: jpg DSCF6565.jpg (95.1 KB, 55 views)
File Type: jpg DSCF6564.jpg (186.2 KB, 55 views)
pdavid is offline   Reply With Quote
Old 06-27-2019, 03:21 AM   #3
pdavid
Senior Member
 
Join Date: Jan 2011
My Country: Hungary
Line Voltage: 230V/50Hz
Posts: 186
Default Re: Videoton VT-110, XT clone PSU repair

Just noticed that most of pictures don't show up in the first post. I'll try to get it fixed.
pdavid is offline   Reply With Quote
Old 06-28-2019, 09:15 AM   #4
pdavid
Senior Member
 
Join Date: Jan 2011
My Country: Hungary
Line Voltage: 230V/50Hz
Posts: 186
Default Re: Videoton VT-110, XT clone PSU repair

Attached the missing pictures of the internals/parts.
I'll need to gather some minor parts like proper sized silicone heat transfer/insulation pads, small caps, spacers, etc. Probably going to reassamble and test the unit this weekend.
Attached Images
File Type: jpg DSCF6517.jpg (204.2 KB, 7 views)
File Type: jpg DSCF6518.jpg (182.7 KB, 4 views)
File Type: jpg DSCF6519.jpg (52.2 KB, 7 views)
File Type: jpg DSCF6521.jpg (83.6 KB, 5 views)
File Type: jpg DSCF6520.jpg (298.1 KB, 9 views)
File Type: jpg DSCF6522.jpg (193.7 KB, 4 views)
File Type: jpg DSCF6526.jpg (251.8 KB, 5 views)
File Type: jpg DSCF6531.jpg (213.3 KB, 5 views)
File Type: jpg DSCF6532.jpg (133.7 KB, 7 views)
File Type: jpg IMG_20190604_110712.jpg (56.2 KB, 7 views)
File Type: jpg DSCF6533.jpg (104.9 KB, 6 views)
File Type: jpg DSCF6535.jpg (415.6 KB, 5 views)
File Type: jpg DSCF6536.jpg (397.8 KB, 8 views)
File Type: jpg DSCF6537.jpg (359.8 KB, 4 views)
File Type: jpg DSCF6539.jpg (131.1 KB, 6 views)
File Type: jpg DSCF6541.jpg (198.5 KB, 6 views)
File Type: jpg DSCF6546.jpg (112.7 KB, 7 views)
File Type: jpg DSCF6542.jpg (261.4 KB, 7 views)
File Type: jpg DSCF6544.jpg (206.1 KB, 5 views)
pdavid is offline   Reply With Quote
Old 06-28-2019, 11:20 AM   #5
PeteS in CA
Badcaps Veteran
 
PeteS in CA's Avatar
 
Join Date: Aug 2005
City & State: San Jose, CA
My Country: USA, Unsure of Planet
Line Voltage: 120VAC, 60Hz & 115VAC, 400Hz
I'm a: Professional Tech
Posts: 2,856
Default Re: Videoton VT-110, XT clone PSU repair

1. The input electrolytics were made by Roederstein.

2. The date codes on the PWM and supervisor are 1988, "SG" being Silicon General, the creator of those ICs.

3. However, the date code on the Matsushita fan is 1993

4. It looks like that may be a half-bridge rather than a push-pull inverter, with TR2 providing gate drive.

5. FT2 looks like it might be the output inductor. If it is and since its core is N27 ferrite the core is probably gapped, either with a spacer between the core halves or it is a machined pair. I'm pretty sure an ungapped ferrite core would saturate so that inductance would be minimal. Powdered iron cores are common in SMPS because they have an inherent distributed gap.

6. IIRC, N27 ferrite is a fairly/very old material type, with multiple sources having equivalent materials. N27 was originally made by Siemens.

7. Regarding ferrite cores generally, back when that power supply was made, the lead times for cores, unless they were in stock, tended to be awful. Core pairs with a machined gap - like that output inductor might be - tended to be made-to-order, even though they might be a catalog item, and the lead times could be on the order of a year. IIRC, in it's flyback designs, in which the main "transformer" core was gapped, Boschert used spacers to set the gap.
__________________
PeteS in CA

Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.

Where might is right
There is no right.
- Sophocles in "Antigone"
****************************
All that is gold does not glitter,
Not all those who wander are lost;
- J.R.R. Tolkien, The Fellowship of the Ring
****************************
To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.

Last edited by PeteS in CA; 06-28-2019 at 11:41 AM..
PeteS in CA is offline   Reply With Quote
Old 06-28-2019, 12:16 PM   #6
pdavid
Senior Member
 
Join Date: Jan 2011
My Country: Hungary
Line Voltage: 230V/50Hz
Posts: 186
Default Re: Videoton VT-110, XT clone PSU repair

Quote:
Originally Posted by PeteS in CA View Post
3. However, the date code on the Matsushita fan is 1993
The fan might not be the original after all. Maybe the psu was serviced before. All I know is that the Videoton PC production was halted in 1989.

Quote:
Originally Posted by PeteS in CA View Post
4. It looks like that may be a half-bridge rather than a push-pull inverter, with TR2 providing gate drive.
You are correct. I've drawn back the and it is in fact half bridge configuration. The FETs are switched through TR2.

Quote:
Originally Posted by PeteS in CA View Post
5. FT2 looks like it might be the output inductor. If it is and since its core is N27 ferrite the core is probably gapped, either with a spacer between the core halves or it is a machined pair. I'm pretty sure an ungapped ferrite core would saturate so that inductance would be minimal. Powdered iron cores are common in SMPS because they have an inherent distributed gap.
There are separators between the core halves on FT2 and it's bonded together with silicone.
Attached Images
File Type: jpg DSCF6567.jpg (426.8 KB, 36 views)
pdavid is offline   Reply With Quote
Old 07-06-2019, 08:08 PM   #7
momaka
Badcaps Veteran
 
momaka's Avatar
 
Join Date: May 2008
City & State: VA (NoVA)
My Country: U.S.A.
Line Voltage: 120 VAC, 60 Hz
I'm a: Hobbyist Tech
Posts: 8,952
Default Re: Videoton VT-110, XT clone PSU repair

Nice repair/restoration. Really great to see an old PSU like that brought back to life.

If you need more AT PSUs let me know. I do have an old Astec that's built like a tank. Not sure if it works or not, but it's an Astec.
momaka is offline   Reply With Quote
Old 07-08-2019, 06:39 AM   #8
pdavid
Senior Member
 
Join Date: Jan 2011
My Country: Hungary
Line Voltage: 230V/50Hz
Posts: 186
Default Re: Videoton VT-110, XT clone PSU repair

Quote:
Originally Posted by momaka View Post
Nice repair/restoration. Really great to see an old PSU like that brought back to life.
Hey thanks! I'd really hate to see old historical stuff like this ending up on some e-waste pile. I also have some old Astec units. Even some server grade ones with APFC, from 1995!

Managed to continue a bit with the repair.

A tab from the heatsink goes under the main trafo. I speculate that if too much pressure is applied by the fastened screws the ferrite core might crack again. I put some thin insulation tape around that tab so it won't interface hard with the core.


Taps coming out from the main trafo have damaged insulation. Seem to have flaked off at some points. I put heatshrink tubing over some of those wires so they won't short each other.


All the new low voltage caps have higher temp and ripple current rating then the old ones. Physical size isn't a problem here thankfully. Plenty of room.


The pcb has a spot for a fuse (B1) that was original jumped with a piece of wire since the unit has fuses elsewhere on the input. Maybe I could install a choke here for EMI filtering purposes.

Also I noticed the the unit doesn't generate a Power Good output signal. The wiring is there but the trace just ends up in a via that goes nowhere!
Could just wire it to 5V but I'm planning to install some 100ms delay circuit. Have to implement something since even the low end XT AT motherboards are picky about missing PG.

The X2 caps I have won't fit between the other EMI parts like the original did. It has to stand away from the pcb a bit.


I had to source some other parts and I'm still waiting stuff to arrive from farnell. I'm not in a hurry with this one anyway.
Attached Images
File Type: jpg DSCF6593.jpg (336.7 KB, 15 views)
File Type: jpg DSCF6594.jpg (212.6 KB, 14 views)
File Type: jpg DSCF6592.jpg (368.9 KB, 16 views)
File Type: jpg DSCF6586.jpg (406.7 KB, 16 views)

Last edited by pdavid; 07-08-2019 at 06:40 AM..
pdavid is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2019
Powered by vBulletin ®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 01:54 AM.
Did you find this forum helpful?