In a run of bad luck, I've just had my second monitor (CTM644) die within two weeks of my first one :o
https://www.cpcwiki.eu/forum/hardware-related/ctm640-dead/ (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 (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 (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 (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 :-[
Caps that can go bang on discharge:
C505 400V :o
C506 250V
C430 250V
C401 160V
C515 160V
C419 160V
Replacement diode from equivalents (Among others on Aliexpress). Getting another STK from ebay for this one
https://vi.aliexpress.com/item/32667705821.htm (https://vi.aliexpress.com/item/32667705821.htm)
Happy to say finally this is now working :D
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/ (https://www.cpcwiki.eu/forum/hardware-related/ctm-640-colour-monitor-repair/25/)
Quote from: darkhalf on 07:23, 15 July 23Caps that can go bang on discharge:
C505 400V :o
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 ?
QuoteThat 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
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.
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
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