SC1224 JVC Transformer Specs?

[mattsoft]

Hi all - so I have a non-functioning SC1224 RGB (JVC) monitor and I've been able to trace the problem (I think) to the power transfer. My multi is giving me nothing when checking resistance across the 2 AC pins, however I am getting a reading on the DC pins (out of circuit). So I think the wire coil on the AC input side may be toast. It's a JVC CE40489‑00A transformer but I cannot find the specs for it anywhere to locate a replacement, and I can't find schematics for the JVC model SC1224. Anyone know the specs or a replacement? Thanks!

Edited January 11, 2021 by mattsoft

[TGB1718]

If it's a switch mode power supply (I don't know if it is) there may be no reading across the AC input pins.

 

Can you confirm what type it is, can you open it and take a photo ?

 

Edit: I just found this, hope it helps

 

atari_sc1224_sch_1986.pdf

Edited January 11, 2021 by TGB1718

[mattsoft]

Attached is a picture of the power supply portion of the board. The transformer is in the bottom right.

 

I did see those schematics but they are so low-res I can't make out the voltages coming out of the output.

[TGB1718]

It's a switch mode power supply, if it was just a step down transformer, the transformer would be much bigger,

(would be virtually the whole PSU itself)

 

I see there's a fuse in there, have you checked it ?

 

Also worth checking the things that get hot, the 7W resistor above the fuse and the high wattage

resistor mounted on the heat sink

 

[mattsoft]

Both fuses test good. I have replaced the 2 electrolytic caps in there as well for good measure. Tested continuity between all components that I can see and all is good.

 

When powered on, I'm not getting any DC on the right side of the transformer which is the tail end of the power supply. I have not worked back through the power supply to test for individual items (beyond the fuses and the 2 electrolytic caps). Using that info, since there is no DC power coming out, I'm guessing something in the PSU is dead. I'll start connecting leads and checking for voltages up the circuit. And yes, I'm aware that mains current is deadly. I will use clip leads so I'm not dinking around inside a live power supply.  Thanks!

[mattsoft]

Looking at this board, the CE40489 transformer is receiving 120v AC and should be stepping it down, but I don't know to what. I've tested the power supply while on and can measure 120v AC at the input of the CE40489 transformer, but I'm getting 0v AC on the output side. So I really think this transformer has short in it. Maybe I'll try to find another monitor with the same transformer in it so I can figure out what the output voltage should be. 

Edited January 12, 2021 by mattsoft

[+kheller2]

Seems the SC1224 manual at archive.org isn't complete.  See if this helps until I can get these scanned in.

 

[mattsoft]

Thanks for scan kheller2 but I think this might be for a different version of the SC1224, maybe not. Atari made 3 versions, each from a different manufacturer. The model I have is "version 2" from JVC. Goldstar and some other manufacturer made the other 2. All components on your schematic have slightly different labels than what's on my board, though the schematic appears to match the layout of the power supply. Do you know for sure this is for the JVC model? THANKS!

[+kheller2]

On 1/12/2021 at 10:24 PM, mattsoft said:

Thanks for scan kheller2 but I think this might be for a different version of the SC1224, maybe not. Atari made 3 versions, each from a different manufacturer. The model I have is "version 2" from JVC. Goldstar and some other manufacturer made the other 2. All components on your schematic have slightly different labels than what's on my board, though the schematic appears to match the layout of the power supply. Do you know for sure this is for the JVC model? THANKS!

The FSM is for Version 2.  Two knobs in front, are the JVC version I believe.   I have the Trouble shooting section with schematics from Dec 1985 and also Feb 1986.  They just don't fit on my scanner.

[mattsoft]

1 minute ago, kheller2 said:

The FSM is for Version 2.  Two knobs in front, are the JVC version I believe.   I have the Trouble shooting section with schematics from Dec 1985 and also Feb 1986.  They just don't fit on my scanner.

Yup, that's the right model -- 2 knobs on the front. Any chance you could take hi-res photos with a mobile? archive.org could use those!

 

Thanks!

[mattsoft]

Just an update: I picked up a working SC1224 JVC model and tore it apart. When testing the PSU on the working monitor and comparing it against my non-working monitor, I can confirm that CE40489 in my non-working monitor is the culprit. This transformer at T901 is 115V on the input (primary) and 16.5V on the output (secondary). I cannot find a replacement transformer that has pins in the same arrangement, so I'm going to find something with matching specs and try to carefully wire it in and secure it with hot glue.

Edited January 17, 2021 by mattsoft

[TheReducer]

@mattsoft

Did you find some reasonable replacement transformer that you could wire in place?

I need to find a replacement for the same T901 (CE40489) as well from a Commodore 1702 monitor (also made by JVC).

I'd appreciate anything you could share about your experience replacing this transformer, please.  Pictures of how you fastened the replacement on the board would be great too, please.  Thanks!

Even just the 16.5V output spec you listed above has already been helpful to me.  : )

 

Here's one replacement option I'm considering:

https://www.digikey.ca/en/products/detail/triad-magnetics/FP34-170/242468?s=N4IgTCBcDaIDoBcBiAFAzAFgLQEYDsADCALoC%2BQA

 

I've also opened up the existing transformer and confirmed the secondary winding is fine, but the primary winding is severed.  I'm going to try rewinding the primary to see if I can repair the transformer before buying a replacement.

[mattsoft]

13 hours ago, TheReducer said:

@mattsoft

Did you find some reasonable replacement transformer that you could wire in place?

I need to find a replacement for the same T901 (CE40489) as well from a Commodore 1702 monitor (also made by JVC).

I'd appreciate anything you could share about your experience replacing this transformer, please.  Pictures of how you fastened the replacement on the board would be great too, please.  Thanks!

Even just the 16.5V output spec you listed above has already been helpful to me.  : )

 

Here's one replacement option I'm considering:

https://www.digikey.ca/en/products/detail/triad-magnetics/FP34-170/242468?s=N4IgTCBcDaIDoBcBiAFAzAFgLQEYDsADCALoC%2BQA

 

I've also opened up the existing transformer and confirmed the secondary winding is fine, but the primary winding is severed.  I'm going to try rewinding the primary to see if I can repair the transformer before buying a replacement.

Sorry, I ended up not doing anything. The monitor is sitting dead in the basement.