strange Defender RAM failure

AMG

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I have a Defender board that gets a RAM failure on every cold start. All RAM chips have been replaced with new 4164's (and power adapter) with no change. But once it's running, it passes the RAM test, and if I hit the reset switch I get the "initial tests indicate unit ok" message. And one time I accidentally turned the machine off and on with only about 3 seconds in between (I would normally never do that), and that time it also said "unit ok". I tried that again a few days later just as a test, and got "unit okay" yet again. The game plays fine after the initial failure message, but every time it starts I get the RAM failure. The machine has a switcher, and the RAM chips are getting 5.02 volts measured at the chip. Any clues what could cause the powerup RAM test to fail?
 
As a best guess? Poor solder joint somewhere. Heats up enough in a few seconds to hold a better connection for the duration.
 
Would it be a reasonable test for such a solder joint to leave the machine running for an hour or so, then turn it off, wait about 10 seconds, and fire it up; or might a bad joint cool down too much in even that short a time?
 
I'm willing to go with bad/failing switcher.

I have a switcher in my jamma cab here that causes all sorts of issues when I do a cold start on the machine. After about 30 seconds or so, it fixes itself and runs normal. I haven't checked to see exacltly how it's failing... but I can hear in in the speakers when I first turn the machine on... the "wa-wa-wa-wa-wa" stops after a few seconds and everything is good to go as long as I don't turn the machine off for more than an hour or so... because it'll just do it again.
 
I have a Defender board that gets a RAM failure on every cold start. ...


I vote for socket issue. Take the CPU and ROM board out, unsocket ALL the socketed chips and run the PCBs thru the dishwasher with a cup of vinegar.

Assuming you have low-ion water just let it dry a couple of days. If you get water from the great lakes or other hard water source, rinse VERY well with distilled water.

Inspect and clean all the legs of the decoder ROMs. For that matter, order a new pair from hobbyROMs.

Just my $0.02 worth,
Saltbreez
 
I have another CPU board that works fine in that machine, and the switcher is relatively new, so the switcher should be good. I've had the 5v up as high as 5.15 measured at the leg of the 4164s, with no difference. I've heard about people putting boards in the dishwasher before, and the thought sends chills down my spine! :) But if that's what it takes, so be it. Stupid question: which way should the board go into the dishwasher? Vertical or horizontal? Component side in or out?
 
I have another CPU board that works fine in that machine, and the switcher is relatively new, so the switcher should be good. I've had the 5v up as high as 5.15 measured at the leg of the 4164s, with no difference. I've heard about people putting boards in the dishwasher before, and the thought sends chills down my spine! :) But if that's what it takes, so be it. Stupid question: which way should the board go into the dishwasher? Vertical or horizontal? Component side in or out?

Component side gets hit by the spray... that is all that counts.

Saltbreez

PS, run a hot soapy empty load AFTER you run the PCB and BEFORE you do dishes.
 
If your sink is big enough, just rinse the board in the sink. Use a dilute white vinegar solution to neuralize any battery alkalai and then rinse well and stand on edge to dry. Or put in the oven at very low heat (175 degrees max).Just because a switcher is new does not meen that it necessarily is good.I would also replace the power connectors from the ps board to cpu & rom board. Those IDC connectors are garbage.ken
 
The board went through a wash cycle in the dishwasher along with 1/4 cup distilled white vinegar (that was all that was left), and while all the metal on the board looks bright and shiny, the board itself looks kinda bad. What went in as a dusty but green board came out chalky greenish-white, so cloudy you can barely read the Williams logo above where the battery holder goes. After I got it out of the dishwasher, I rinsed it well first with tap water and then with distilled water. Is the color change normal? Might the board have been damaged? Is there anything I should do to it to prevent further harm? It'll be a couple of days dry time before I can hook it up and try it out, but it's looking pretty sad at the moment.
 
Put that board into your oven @ its lowest setting to speed the drying time from days to a couple hours. No more than 200°. Won't affect how it looks, but it'll be dry.

Do you have particularly mineralized water?
 
The board went through a wash cycle in the dishwasher along with 1/4 cup distilled white vinegar (that was all that was left), and while all the metal on the board looks bright and shiny, the board itself looks kinda bad. What went in as a dusty but green board came out chalky greenish-white, so cloudy you can barely read the Williams logo above where the battery holder goes. After I got it out of the dishwasher, I rinsed it well first with tap water and then with distilled water. Is the color change normal? Might the board have been damaged? Is there anything I should do to it to prevent further harm? It'll be a couple of days dry time before I can hook it up and try it out, but it's looking pretty sad at the moment.


Some of the Williams PCBs do this, it has no effect on the functionality. An oven drying will actually reduce this effect, but is not needed.

Saltbreez
 
If your sink is big enough, just rinse the board in the sink. Use a dilute white vinegar solution to neuralize any battery alkalai and then rinse well and stand on edge to dry. Or put in the oven at very low heat (175 degrees max).Just because a switcher is new does not meen that it necessarily is good.I would also replace the power connectors from the ps board to cpu & rom board. Those IDC connectors are garbage.ken

Hey Ken,
The vinegar is not there JUST to neutralize alkali, it also helps to remove the top oxidation layer.

Saltbreez
 
boards in dishwasher.....not a good idea but what is done is done. Dusty boards don't effect the electronics unless it's conductive such as mud or droppings from animals. I have cleaned boards with water, baking soda and a tooth brush but mostly for battery acid damage. A dishwasher is not going to fix bad sockets.

With that said, I seen this problem from time to time with a bad decoder chip. If you have another board try switching the decoder #2 and #3 out. If that still doesn't help it's probably some TTL chip failing that will get worse with time and maybe some day it fail all together and then it will be easy to find for a tech.
 
My Defender booted up to a ROM error a few times and the ROM board is extremely dusty and I gotta clean it.

I fixed my Stargate reset problem partially by cleaning the entire pcb with a wet toothbrush.
 
boards in dishwasher.....not a good idea but what is done is done. Dusty boards don't effect the electronics unless it's conductive such as mud or droppings from animals. I have cleaned boards with water, baking soda and a tooth brush but mostly for battery acid damage. A dishwasher is not going to fix bad sockets.

With that said, I seen this problem from time to time with a bad decoder chip. If you have another board try switching the decoder #2 and #3 out. If that still doesn't help it's probably some TTL chip failing that will get worse with time and maybe some day it fail all together and then it will be easy to find for a tech.


Ask some of the members that worked in shops that serviced equipment from this era, I believe you will be surprised at how many PCBs have been thru dishwashers.

Saltbreez
 
boards in dishwasher.....not a good idea but what is done is done. Dusty boards don't effect the electronics unless it's conductive such as mud or droppings from animals. I have cleaned boards with water, baking soda and a tooth brush but mostly for battery acid damage. A dishwasher is not going to fix bad sockets.

With that said, I seen this problem from time to time with a bad decoder chip. If you have another board try switching the decoder #2 and #3 out. If that still doesn't help it's probably some TTL chip failing that will get worse with time and maybe some day it fail all together and then it will be easy to find for a tech.

Ask some of the members that worked in shops that serviced equipment from this era, I believe you will be surprised at how many PCBs have been thru dishwashers.

Saltbreez

A dishwasher is just a handy way to run boards through a wash cycle. If you are squeamish about throwing them in, then get out the garden hose or use the sink. The end result is the same, A nice clean board that you can inspect without worrying that a cracked trace might be hiding under a layer of dust. With Williams boards I usually use 90% iopropyl alcohol on a rag because of the paper labels, but for boards that don't have labels or stickers, I'll use the garden hose, a quick alcohol bath or a trip into the oven (or my garage in summer, some effect) to dry.

ken
 
It's Alive!

I put all the chips back on the board, hooked it up, and no change. Still the initial RAM failure at boot but not at any other time. Taking the suggestion from Rhombus, I tried the decoder chips from my good board and it's "unit ok"! In this case, it's decoder 3 that caused the problem. Thanks to all for the help, it's great to have this board working properly. Does anyone know if there's a way, short of spray paint ;), to get rid of the chalkiness? It's so hazy that you can't see the traces on the top of the board anymore.
 
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