CTM644 went bang!

[darkhalf]

In a run of bad luck, I've just had my second monitor (CTM644) die within two weeks of my first one 
https://www.cpcwiki.eu/forum/hardware-related/ctm640-dead/

5V/12V Power wasn't even connected (only the DIN to my 464plus). There was a bang when switching on, and the fuse has blown into pieces! Transformer appears okay and the regulator pins measured so far appear ok. 

What has been taken out are two of the rectifier diodes D501 and D504 showing open circuit. D502 and D503 measure 0.5 out of circuit one way only

So far diodes are a 20E10
https://www.datasheets360.com/pdf/8218798635405102001

Found a spreadsheet lining these upto:

Topdiode

PANJIT

Taiwan Semiconductor

IR

FAGOR

LITE-ON

RL207

PS2010

2A07

20E10

RF2007

LT2A07

RL207 as a market place item
https://www.digikey.com.au/en/products/detail/nextgen-components/RL207/15517703

Other lines like 20E10/PS2010 shows up in common anode 3 pin variants only. Would something like this work?
https://www.digikey.com.au/en/products/detail/vishay-general-semiconductor-diodes-division/1N5408-E3-54/76461

This is only the first part of the problem, so need to work out what caused this 

[darkhalf]

Caps that can go bang on discharge: 
C505 400V 
C506 250V

C430 250V

C401 160V
C515 160V

C419 160V

[darkhalf]

Replacement diode from equivalents (Among others on Aliexpress). Getting another STK from ebay for this one
https://vi.aliexpress.com/item/32667705821.htm

[darkhalf]

Happy to say finally this is now working 

Details in below thread. Flyback failure was the cause. Needed STK7308 regulator, several fusible resistors, numerous diodes and last piece was the LA7800 IC (no picture)
https://www.cpcwiki.eu/forum/hardware-related/ctm-640-colour-monitor-repair/25/

[SerErris]

Caps that can go bang on discharge:
C505 400V 
C506 250V

C430 250V

C401 160V
C515 160V

C419 160V

That is why you should put a resistor in between for discharging? Isnt that what you learn in electronics 1:1 ? 

[darkhalf]

That is why you should put a resistor in between for discharging?

I used 2 x 5K 5W resistors on these which did about a 2-10 second discharge. The 240V ones took longer than I expected.

@SerErris thanks but your feedback is a bit late. Fortunately, pledg and bryce were able to provide useful information for assisting me repair this. However if you have some input on where I can source LM78MG regulators on that would be helpful for my second monitor (CTM640) needing a few more parts. Thanks

[SerErris]

According to this post https://www.eevblog.com/forum/repair/substitute-for-ua78mgu1c/

you should be able to substitute it with NTE953, which is available here (as an example):
https://www.tme.eu/at/details/nte953/geregelte-spannungsstabilisatoren/nte-electronics/

Here is the datasheet:
https://www.tme.eu/Document/45874cc1a9dd66d46d43e8afba3920df/nte953.pdf

Looking at the datasheet has pretty much all the same characteristics or much better.

[SerErris]

https://elw-elektronik.com/UA-78-MG-4-TERMINAL-ADJUSTABLE-VOLTAGE-REGULATOR

https://www.ebay.de/itm/222233608495?chn=ps&mkevt=1&mkcid=28

https://www.amazon.de/-/en/pieces-UA79MGU1C-housing-4-terminal-adjustable/dp/B0838YMMMG

[darkhalf]

Thanks for that. Found those ones on ebay too. I had a dead transistor nearby, so after replacing this the regulator showed voltage. Few more parts later the CTM640 is also going too. I'll have to compile a component list and links