A tale of two Neo Geo boards...

channelmanic

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Or...

WHY THE F*** DO PEOPLE DO WHAT THEY SHOULD NOT...???

In the auction before last I bought several boxes of parts boards and in those were two Neo Geo MV4 bottom boards. I thought, hey... I need some bottom boards to use for advance replacements. Should be an easy fix.

WRONG.

Board 1: BIOS has been replaced with an EPROM. Someone replaced a surface mount chip and did a terrible job of soldering. It's missing a pad on pin 15 and has an extra pad on pin 2???

Board 2: Missing the BIOS chip. They pulled the chip from this one and here's where pin 2 is missing it's solder pad. The also pulled pin 28's pad but it's still attached to the heavy power trace. They tried replacing the Z80 and damaged 2 traces - one on each end of the chip - by trying to twist a large screwdriver under it to lift the chip. Sigh. Then they tried to patch the traces and used machine pin SIP sockets to seat a replacement Z80. Yuck.

Both boards look like a ham fisted monkey tried to solder on them. Since I need some advance replacement boards I dive in and see if these boards can be saved.

So... for starters... resoldered the SRAM chip on Board 1. OOPS. They didn't clean the pins on the SRAM before trying to reuse it. The chip is about 1 to 2 mm off the board surface. Sigh. Fixed the soldering issues. Removed the extra pad. Place 1 jumper wire to fix the missing pad. Now it fires up and has a UniBIOS in it (nice touch!), but has a Backup RAM Error. Replace the backup RAM. It works, but needs an audio cap kit.

Board 2... Install a BIOS chip. Clean up the pads, straighten out the pad for pin 28, install a new SRAM, and jumper the busted pad with some 30ga Kynar. Test the board and get a (GASP!) Z80 Error. Remove the kludgey socket and jumpers. Trace out all connections from the Z80. Install a new socket and use 30ga Kynar to jumper the 2 busted traces.

Still a Z80 Error. Replace the SM1 ROM and the board fires up but has no audio. Look closely. They desoldered the audio amp chip but left it on the board! Sigh. Resoldered the audio chip and tried again. No audio. Check the YM3016 DAC with the logic probe and hear the audio signals making it to the analog section from the digital. Crank the volume and put my ear next to the speaker and barely hear the audio. Time for a cap kit.

I'm about to fit a top board on these and test 'em with carts before jumping in with doing the cap kit.

It's EASY to do surface mount soldering with a minimum of tools. The next repair party I have I'll set some scrap boards on the benches and let folks play after showing some tidbits. Key items: Don't pull pads (duh!), you CAN reuse chips, but damnit... you need to prep the pins on them AND prep the pads by cleaning them and laying down some liquid rosin flux so that A) the chips are physically sitting on the board and B) you get a good, stable solder connection.

Chips can be pulled by using solder, chipquik, special tweezer irons, hot air, small diagonal cutters, razor knives, or other techiques. Putting them down requires just some liquid rosin flux and a hot iron. Oh, and a steady hand.

Ham fisted monkies need not apply.
 
I see it a lot, the problem is that very few people actually have the minimum tools required. Their soldering iron is either something they found in their dad's shed left over from his days as a plumber, or they spend the absolute minumum on a non temperature controlled one which gets so hot the flux vapourises out of sheer terror, not that they know what flux is, or what it's for.

The worst on I got was a board whose owner had been asking for help on the local forum. I was too busy to help but offered some suggestions. A week or so later he was still looking for help and I caved, only to find that he had sent the board to a mate of his who "knows about electronics" who had taken the chips I had said *might* be involved off the board. He hadnt been able to do anything with them once they were off the board so I am not sure why he bothered, and by taken off the board I mean RIPPED. Missing plate through holes, torn tracks, pins of chips bent every direction, 5V pin snapped off the BIOS ROM. Following this stirling effort he then proceded to clean the board, with WD40. So what I got was a soggy stinking slippery board with about an hours worth of repairs before I could even get to replacing the single bad CXK SRAM chip that caused the original fault.

Turns out the guy who knows electronics is an auto technician, I had visions of him using a soldering iron more useful for welding ampy ground wires to car chassis than for micro surgery.
 
i gots me my trust 200watt 1" flat sodering gun, lets me fixed that surface mount chips..
 
I see it a lot, the problem is that very few people actually have the minimum tools required. Their soldering iron is either something they found in their dad's shed left over from his days as a plumber, or they spend the absolute minumum on a non temperature controlled one which gets so hot the flux vapourises out of sheer terror, not that they know what flux is, or what it's for.

The worst on I got was a board whose owner had been asking for help on the local forum. I was too busy to help but offered some suggestions. A week or so later he was still looking for help and I caved, only to find that he had sent the board to a mate of his who "knows about electronics" who had taken the chips I had said *might* be involved off the board. He hadnt been able to do anything with them once they were off the board so I am not sure why he bothered, and by taken off the board I mean RIPPED. Missing plate through holes, torn tracks, pins of chips bent every direction, 5V pin snapped off the BIOS ROM. Following this stirling effort he then proceded to clean the board, with WD40. So what I got was a soggy stinking slippery board with about an hours worth of repairs before I could even get to replacing the single bad CXK SRAM chip that caused the original fault.

Turns out the guy who knows electronics is an auto technician, I had visions of him using a soldering iron more useful for welding ampy ground wires to car chassis than for micro surgery.

I friend of mine just passed me a Track & Field PCB he got from someone as non-working. A transistor had been ripped off the board, and four TTL removed very badly, lifting the copper traces with the ICs <SIGH>

It takes alot of time to learn to solder and desolder properly. I've been doing it for 15 years now, and still think there is room for improvement.

Im at a place now where I have good success repairing PCBs, but it took a while to get there, alot of reading and practice. Having said that, I had a head start, I've always had a good understanding of electric circuits but not IC's.

It still amazes me how many people think they can learn to repair PCBs in a weekend. It can be done, but takes skill, time, ALOT of reading and discipline.

I learnt so much from channelmanic's and womble's Repair Logs, thank you guys.
 
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It takes alot of time to learn to solder and desolder properly. I've been doing it for 15 years now, and still think there is room for improvement.

Yes, agreed 100%. I've been soldering for a little over 25 years. My dad had a workshop, and as soon as I showed any interest (around 5 years old) began teaching me to solder. To this day, I still pick up tips and tricks. Not only that, but as time goes on I improve and upgrade equipment which I am finding is nearly as important as the skill of how to use the equipment.

(Not to derail the thread, but...) For those that are interested there are awesome tutorials on YouTube for soldering.

I learnt so much from channelmanic's and womble's Repair Logs, thank you guys.

This, x1000. I can't thank these guys enough for the detailed repair logs. I've known about ChannelManic's repair logs for a while, but I recently found the Retro Computer Museum (and Womble's logs) and have been reading them from the beginning. I have also promised myself that this will be the ONLY reason I go to the Retro Computer Museum website, as I think it would be just as dangerous of a place for me as this arcade forum. Although I know it will only be a matter of time until I hit that forum just as regularly as this one. :)

ChannelManic: This particular repair log is awesome, as I've been working on Neo Geo boards of-late and have been trying to build my knowledge of their inner workings. I had one that I've been working on an audio issue... Wasted so much time on it, did the cap kit, checked traces, hunted the board for audio signals (trying to trace back where the issue was), etc... Just found out that the cart I was using for testing has the audio issue. Ugh. Always start with the simple stuff, right? Hahah.

Speaking of the retro computers (and totally off-topic), I just picked up a Fujitsu Stylistic LT to add to my collection of Retro Computers.

StylisticLT.jpg
 
Very cool. I don't know if I'd classify a Stylistic as "retro", however... :D

-Ian

Personally, I have a wide definition of retro, but also collect everything within that definition. From TI99, Sinclair, etc... all the way to anything that's "no longer reasonably usable on a daily basis", like the Stylistic. I think this comes from me being a "computer guy", and finding anything but the newest and fastest computers to be a drag to use. I do agree that by standard definition, the word "retro" might be a bit of a stretch to apply to the Stylistic. I've just not found a better word to use yet. :)
 
To add insult to injury, board 1 with the UniBIOS STILL had bad Video RAM. The guy replaced the WRONG ONE. It was the other one that was bad!

Oh, and for those of you unfamiliar with the UniBIOS - it will bypass self tests so you can have a game with the bad RAM boot, but you'll run into headaches. I yanked it and put the original BIOS in it to go through all the self tests to find the other bad RAM.

It's replaced and both boards have been tested with an upper and now just need cap kits.
 
<snip>

It takes alot of time to learn to solder and desolder properly. I've been doing it for 15 years now, and still think there is room for improvement.

<snip>

Yea, it takes a long time to get good, but it really doesn't take much time at all to get to 'competent'. As in, able to pull and replace chips without damaging the board.

I'm a software guy, and I've soldered on-and-off for 20 or so years (with a couple of those under the tutelage of a REALLY good lab tech), so I'm not great at it, but I can get by without damaging stuff and I've had no problems pulling and replacing chips and connectors and whatnot on numerous boards. These guys could be doing better if they just look at what they are doing and stop when it gets beyond them.
 
Meant to say, Do you have what the pins connect to from the z80 to the pcb?

Example: A1 connects to what chip and pin number?
 
Personally, I have a wide definition of retro, but also collect everything within that definition. From TI99, Sinclair, etc... all the way to anything that's "no longer reasonably usable on a daily basis", like the Stylistic. I think this comes from me being a "computer guy", and finding anything but the newest and fastest computers to be a drag to use. I do agree that by standard definition, the word "retro" might be a bit of a stretch to apply to the Stylistic. I've just not found a better word to use yet. :)

I am still looking for an older KIM-1 micro computer. My first computer if you call it that.

I am having a hard enough time with soldering my Galaga boards, I would just send out any surface mount repair. Part of my problem is I am getting older and my eyes are going bad.

Equipment would help also. I am still looking for a magnifier with the light around it.
 
Meant to say, Do you have what the pins connect to from the z80 to the pcb?

Example: A1 connects to what chip and pin number?

Nope.

It's easy to figure out the connectivity between the Address and Data Busses and the Z80, SRAM, SM1 ROM, and the YM2610 from the data sheets.

The address decoding, enable lines, IRQs, R/W, etc, are a different story.

Whatch got going on?
 
I have have use a Kid's usb microscope to look for breaks in traces and extra small SMT parts. Just be careful if you are soldering around it due to fact that the lens is normally made out of plastic.
 
Just finished the cap kit and new battery on the first board and it sounds/works perfect. :)
 
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