I think my Japanese PSU is bad?

Mobsie · Post by **Mobsie** » Mon Jan 24, 2022 12:03 pm

Great, thank you.
Here the Colecovision article:
https://console5.com/wiki/Colecovision_ ... dification

Scouter3d · Post by **Scouter3d** » Mon Jan 24, 2022 12:16 pm

Hi Mobsie,

the CV uses +12V in 3 other places, the TBA520 Videomixer, the Sound-amplifier circuit and on some models the HF Modulator...
the -5V seem to be "only" used on the RAMs...

PS: on my "workbench-Creativision" i have replaced all 4116 RAMs with 41256 (with modifications) which do not need the 2 additional voltages a long time ago...

Cheers, TOM:0)

Ransom · Post by **Ransom** » Mon Jan 24, 2022 2:41 pm

Thanks Tom. For the ground I mostly used the motherboard ground plane strip that the metal enclosure parts plug into, I tried to check my readings as suggested but I couldn't get the machine to get out of "black screen" and run correctly - but they did match as far as the "black screen" low voltage readings went.

Actually it ran for 2 seconds once - but I noticed a loud buzzing noise coming from the AC power adapter brick during only that two seconds, that can't be good, maybe it really is about to die/explode.

Pics? Sure, hope you like 'em big

https://rtsoft.com/images/retro/creativision_jp_1.jpg
https://rtsoft.com/images/retro/creativision_jp_2.jpg
https://rtsoft.com/images/retro/creativision_jp_3.jpg
https://rtsoft.com/images/retro/creativision_jp_4.jpg
https://rtsoft.com/images/retro/creativision_jp_5.jpg
https://rtsoft.com/images/retro/creativision_jp_6.jpg
https://rtsoft.com/images/retro/creativision_jp_7.jpg

Scouter3d · Post by **Scouter3d** » Mon Jan 24, 2022 4:11 pm

Hi,

thanks for the pictures!

I guess you own some other 9V DC powersupply (around 1A ore more)? you could try to connect it to the CV instead of the original PSU (use only the two pins labeled -9V and +9V on the original PSU) and meassure the 5V line only with this 9V supply ... If you get stable 5V the 7805 should be ok and the fault is somewhere else...

what makes me suspicious is the around 7V you meassured instead of 5V, which is nearly 12V-5V...

Cheers, TOM:0)

Scouter3d · Post by **Scouter3d** » Mon Jan 24, 2022 4:22 pm

To Mobsie, here is how to convert 4164 or 41256 to 4116 so no +12V and -5V is needed (at least for the RAMs :0))

4116_ram_replace.jpg

Mobsie · Post by **Mobsie** » Mon Jan 24, 2022 5:27 pm

Great

thank you

cheshirenoir · Post by **cheshirenoir** » Mon Jan 24, 2022 11:52 pm

7805 would be where I'd start. They're notorious for failing.
(In fact I need to replace the one in mine)
Tempted to replace it (and the 7812) with TracoPower micro switchmode regulators instead. They run so much cooler.

Chesh

Ransom · Post by **Ransom** » Tue Jan 25, 2022 4:44 am

Thanks, it works!!! For anyone interested, here are the steps and issues I went through:

* Replaced the 7805 with a LM7805CV, the only kind I have on hand. Before installing I verified it output 5V with 9V in, in a test environment
* For fun, tested the old 7805 that was pulled, sure enough, with 9V in it *was* outputting 7V. Definitely was broken
* Machine still didn't work, power supply not supplying +9V correctly
* As Tom suggested, wired a power supply replacement, set to 9V and 1 amp
* Still didn't work - 9v power supply now drawing 0.5 amp but instead of 5V output, LM7805CV is breaking down and outputting only around 3V, measuring the 5+ pin on memory also shows 3v, so not enough to work
* At this point I tested some other LM7805CV's I had under various loads in a test environment and they ALL break down at around 0.4 amps. They are rated at 1 AMP I believe but I guess that's just how it is? Low quality maybe
* I couldn't find a 7805 to order 1-day shipping that is 1.5amp or higher, I ordered a TracoPower replacement thinking it might work as they are more efficient despite also being rated at 1 amp, but it doesn't come for two days ($15, stuff can be costly when I use amazon jp, ouch)
* LD1085V50 (3 amp!) would probably work, can't find a way to order one quick though, will aliexpress some for next time though

So not wanting to wait for the right part I removed the LM7805CV from the board and just directly wired 5V 1amp from the power supply instead and it works! Hopefully that's safe to do.

So I'm thinking maybe just set things up to require two power supplies, the old one (which I don't trust...will definitely never let it run unattended) and a 5v 1amp. Not elegant but should work

Scouter3d · Post by **Scouter3d** » Tue Jan 25, 2022 8:41 am

Hi Ransom,

congratulations!

I would still go with trying to replace the 7805 (either good strong 7805 or Traco replacement) and use an external 9V Source...
with 5V directly to the board you will have no power on the Cassette-port (maybe someday you want to use the original Tapedeck, my Audiointerface or the CV-Datasette Interface...)

Cheers, TOM:0)

Ransom · Post by **Ransom** » Tue Jan 25, 2022 11:40 am

Ahhh, didn't know that.

I'll try out the Traco then.

I think my Japanese PSU is bad?

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