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  • Joined: 16 May 2020
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Possible to repair this board?
Post Posted: Mon May 25, 2020 11:35 pm
Good afternoon, I have recieved a broken ebay sms board and have another two that have some working parts to use. I have attached images of a board with the closeup being another board with a similar issue. I am not sure how to repair missing pads for the 7805 Voltage regulator any ideas? I hear that sometimes you can scrape copper and and connect the leads to the exposed copper or trace but I dont exactly want to just guess without some helpful input. I know several of these boards have issues with the 7805 so im thinking other parts could be good if I can just get a new 7805 and power the system up. From my reading on the multimeter a lot of other components seem to be good. I recapped the system just to get that out of the way but hope someone would know how to work with this problem or know where and how to route jumper wires. Thanks!
20200525_183724.jpg (1.24 MB)
20200525_183724.jpg

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Possible to repair this board?
Post Posted: Tue May 26, 2020 5:05 am
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I hear that sometimes you can scrape copper and and connect the leads to the exposed copper or trace


That basically is the repair process for broken and missing pads in one sentence.

Gently scrap the lacquer off the traces to expose the copper.

You will need to use some wire to bridge the connection between each pin and its copper track. The extra length of the 7805 pins can also be used instead of the wire by bending them.

Solder the wire to each pin of the 7805 and to its corresponding copper track.

Good luck with the repair.
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Post Posted: Tue May 26, 2020 10:22 pm
You probably don't need to expose the copper. Instead bend the pins through the holes to the legs of the pins nearby. The middle pin (ground) can be bent the other way to the copper border and soldered directly to it (looks like it had been already)
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Post Posted: Wed May 27, 2020 7:12 am
Last edited by dutch4fire on Wed May 27, 2020 11:54 pm; edited 1 time in total
Good deal! Thanks that worked like a charm. I decided to bend the pins for one and jumper the other board to save the shorter legs of a trimmed 7805 I had desoldered (working one).

Good news is both boards power up! Bad news no video or sound :(. I suspected a bad cx chip one one board and had a good working one on a junk part board that was working and swapped the IC Sony CX chips annnnnd its still showing nothing really. Tried on two CRTs with RF and the AV cable (only have one AV cable for the SMS and it did work with my friends SMS so I did not think it was the cable or the tv ports since those seem to work for other devices). I attached the pictures.

Could it be the RAM? If not could I bypass to RGB out. I planned to use my rgb bypass board

Update: I replaced the RAM and VDP. The system powers on and I see some scrolling white lines as it fades to black
I cant understand what could be the issue now!? All repairs Ive seen include combo of 7805, CX Chip, Ram or VDP. The parts were taken from a good known board that I had and that parts board was known to work but had a bad cpu and no power. Some other board issues but ICs seemed to be fine..although how does one test the IC chips as I dont own a Oscilloscope yet.? I did check for continuity and Im getting that too. Weird. I wonder if the 7805 I used from an Amazon kit isnt the right one and jot giving enough power or something so I ordered some 7805 VRs from console5. So right now as far as I know...

1. Powers on
2. Has continuity and also on the IC chips
3. Replaced CX, 2 RAM ICs, and VDP from a good source
4. Replaced DC Jack
5. Replaced fuse by the dc jack (the original was bad)
6. Reflowed solder
7. Used good working AV cables, and power supply
8. Replaced 7805 and soldered as directed above
No smoke, just white scrolling lines and fades to black on two CRTs and even converting to HDMI on my main TV

At this point I could have just bought a good working one off Ebay but jow I need to fix this based off principle alone..damn thing makes me want to rip my eyes out! Still having fun but damnit all....

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Post Posted: Wed May 27, 2020 11:52 pm
Help
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Post Posted: Thu May 28, 2020 12:06 am
You can get a logic probe as a cheaper alternative to an oscilloscope - they're around $20 on Amazon. It's very rare that I have to break out the oscilloscope for most repairs.

You're looking for stuff like:

  • Clock signals
  • Activity on the RAM's data and address pins
  • Activity on the CPU's data and address pins
  • Is the reset pin stuck low?


The horizontal lines on startup are interesting, it is at least obviously generating some video. One pin looks stuck on the cartridge slot, but I assume you're starting it up into the BIOS.

If you have a multimeter (since you're doing continuity checks) are you seeing clean 5V at the power pins of the ICs? That way you'd at least know for sure the 7805 is good.

Good luck!
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Post Posted: Thu May 28, 2020 2:26 am
Thanks!

Well this is the excuse I needed to use some of the remaining stimulus check after bills and donations, wife approved so I am upgradding with a Signstek MESR-100 V2 Auto Ranging in Circuit ESR LCR Meter, Elenco Electronics Lp-560 Logic Probe, and EEVblog Brymen BM235 Multimeter. I am pretty excited about this :)

Okay so I should have what I need to properly diagnose a problem. My meter seems to fo continuity fine but Im not getting acurate readings after testing my computer charger which is brand new and working. It did read .317 V on the first pin of the 7805 and nothing on the output. 5 V pins 2.5mV on VCC for the Sega 315 which tested different on the og board. Other VCC seems off too...maybe it is the 7805 (from amazon kit) thats not a proper one...solder points check out as well as continuity. Dont see anything else weird.
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Post Posted: Thu May 28, 2020 3:18 am
Something has gone really wrong if you are seeing 0.317V at the 7805 and virtually nothing at the 315.

I know you said it was a known-good power supply; can you meter that as well to rule it out? Is anything on the motherboard getting ridiculously hot (shorted?)
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Post Posted: Thu May 28, 2020 4:23 am
Doesnt seem to get hot at all. I feel like my multimeter is not right so Ill wait until Friday when the new one arives and retest. Power supply shows good and tried a newer variable adapter used with my friends SMS fine.

Well shoot....Now I do think something is messed up. The LED lights up, I get only dark black screen now and LED fades to off. :( checked solder job and looks good so I am going to see what the new mm sais and wait for the new 7805 from console5 to come in, resolder those and check again.
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Possible to repair this board?
Post Posted: Sat May 30, 2020 3:46 am
Start by testing and making sure you have a steady and constant 9Vdc or so to the 7805 input when the console is powered on.

Then test and make sure that there is a steady and constant 5Vdc at the 7805 output.

Until the 7805 input and output test well, testing further is pointless.

Good luck.
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