DK Jr Sprite sparkles

[virtvic]

I've just received my DK cabaret cab. I also have 2 DK Jr pcbs I can use with it. They haven't been powered up in a long while. First one has graphical glitches all over the place and most sound and music is gone

The second one had big blocks around a lot of the sprites, but after re seating and cleaning the eprom at 7C, it runs ok, but there are slight sparklies in some of the sprites. Could this be the actual sockets at 7C,7D,7E and 7F? According to the excellent Braze technologies DK Jr technical info page, it seems to point to all those eproms. I have read the data out and confirmed they are all good. I'm just thinking it could be socket problems?

 

[pubjoe]

I had just the reverse with mine last time I tried it. Slight sparkles here and there, then my attempts at cleaning/reseating ended up with those sprite blocks. This was quite a while ago and I haven't been motivated to have another look.

Sorry to interrupt without any help, but I'm keen to follow this.

 

[sukhbir]

To get these boards working in good order I would first give them a service then look for the faults,don’t forget these boards are over 40 years old!

good luck

 

[Mr20to5]

Vic, not a definitive answer, but we had similar issues fixing my PP board. We spent ages chasing ghosts around with suggested chips passing tests when out of the board, etc.

Bit the bullet and changed out ALL the sockets (a lot, a hell of a lot) and whilst this didn't magically fix the board, it eliminated any doubt which allowed the true fault to be found.

For the sake of only changing out 4 sockets it might be worth just doing it for the same reasons?

 

[Georgian2]

If they are flickering or pixels flickering check for floating pins.
An easy way is to run your fingers across the solder side an watch for changes. If any, you can use one finger and locate the exact pin. Takes some practice to master this easy method. It's not always working.

 

[pubjoe]

Donkey Kong Junior Technical Info

I've been working with DK and DKjr boards for about a year now. This page is a collection of information aimed at helping diagnose and fix DK and…

highscoresave.com

Good visual list describing lots of types of graphical errors and the causes. I found a different website dedicated to DKJ repair a while ago and I think that had even more examples, but I'm on break and don't have time to google any further right now.

 

[Mc-Q]

sparkles are usually ram if the sockets are good

 

[virtvic]

Both boards are pretty borked now. I cleaned the 4 suspect sockets are reflowed them (on the better board) to no avail. I’ll check all the EPROMs with hamster’s online Rom repository, then replace the sockets if need be.

What is the best way to test ram, btw?

 

[virtvic]

This is the one that’s still (sort of) working.

 

[virtvic]

After a while the black part of the screen goes green and stays green.

 

[69er]

Hi virtvic I know you like many of us have been in this hobby a long time but for the benefit of newbies or less experienced readers following this ……. Read on …

It’s often easy to see how legs of ICs become tarnished with age (esp. at 40yrs)
Similarly the plug able socket blades do the same and it’s long established that initially a gentle repetitive reseating will sometimes improve conductivity at these points ?
Best simple advice it took to my head in the early days was to get a pencil rubber eraser and rub the gold edge connectors clean on a quite regular period when jamma and electrocoin , & MGVS interchangeable pcbs and NeoGeo came popular as it was better than hauling full cabs in and out of sites often up stairways too !
Not quite so easy to do the same to the host machine loom edge plug though
Sadly it is age that seems to affect the components and years ago I found it’s not always the same ICs that tend to fail so it’s even more frustrating tracking faults like this !

Most confusing is how they work fine one day then next day or short period you get a rogue sprite , letter or block appears or sound goes off etc then Sod’s Law a few days later it can reappear as ok ? Maybe small voltage fluctuations have a minor affect on the circuits ?

I know in our holiday park arcades when caravaner’s all put their kettles on at teatime the arcade supply can reduce from local 220v -230v (wales) down to as low as 205v and fruits reels land between symbols and odd video games reset as the arcade itself also draws a lot of current even at 5 amps per machine,
Coins don’t accept in mars mechs as good as a 10% volt drop transforms the 12v mech supply to 11v too Some (many) fruits have alternative supply input tappings to allow 240 or 220 areas of use. This is also a feature on some video switch mode psu’s ?
Handy when supply voltage varies around parts of the UK and area demand is high?

The other thing that can affect supply variation is loose mains plugs and the terminal screws maybe coming slack or using longer extensions to feed a garage based game at home?
All perhaps worth considering first before chasing ghosts! ……. Hope it helps or reassures?

It’s just a bit of basic experience from 40 years involved it may help a little but perhaps not who really knows it’s like saying “ doctor I am phoning about a rash” ??? Numerous possibilities and cures ???

And is why many techs on here say check your voltage at board entry before you start looking further all good to keep in mind ?

 

[Mc-Q]

i need to stop reading this forum before coffee!!!
you dont clean sockets, you replace them.
i have seen sockets with broken pins under them and even chip pins stuck under them causing intermittent shorts.

also - you shouldnt "re-flow" solder, you should replace it.
old solder may have different composition and mixing metal-blends doesnt always work well.

for testing ram that has intermittent glitching - or suspected glitching, you cant really test it - you can only diagnose it by swapping out for another ram.
sometimes you can find a similar ram on the board for something else and swap them around.

 

[Mc-Q]

Tarnish.
tarnish forms on silver plating, mostly used by texas instruments, fujitsu and general-instrument > now known as Microchip.
you can remove it with tarnish remover liquids but often the metal under it has thinned.

oxidising forms on gold and makes it look dull, no damage though.

biggest problem is corrosion formed by disimilar metals in contact with each other.
specially gold and tin.

if you collect old pc's dont put gold plated sims into tin-plated sockets or they will form black oxide you will have to clean every year.
the same effect happens with chips & chipsockets

 

[69er]

I agree with Mc-Q entirely and thanks for expanding on the detail of metallurgy issues especially solder replacement it’s great info all to consider . I too would fit new sockets at any IC I replace just makes it so much easier should the same fault recur in the future. Sadly smd got far too compact for my 70 year old eyes to adjust.
Happily I have given up board work now but in the early days we had no forums no well known technical advisors and only basic wiring info with no internet but my theory was always if TV was invented in the 30s or thereabouts with zero info then by 1980 with the repairmen who did work behind tv shops to assist a little I found with my career change electronics c&g and Btec HNC I was able to manage r g b monitor repairs and even some ttl game repairs and conversions as new games came out to fit previous galaxian style base pcbs . As boards came common and cheaper second hand in the 90s repairs on site were less urgent and we just swapped cabinets or pcbs and upgraded with new or secondhand on sites. Repaired less and burned the unwanted .. filled skips and tips ….little did we realise as time passed these cabs and games would become so collectible and subsequently rare that home repair has become essential …..

 

[Mc-Q]

indeed,
i am in the middle of repairing a battlezone pcb that somebody in the past wrote off, and removed all the ram and about 10 other chips with a hot-air gun!
LOTS of track repair & cleaning + more cleaning.
gonna mod it for single program rom, single vector-table rom and single ram - just because of the damage!
in the past i would have stripped and binned it!!
now it has to live.