Crest 275HTAG Ultrasonic Cleaner repair

Time for a something a little different, I've had a 30L no name Chinese Ultrasonic cleaner for a couple of years now and it does a good job of cleaning arcade boards. The problem is it isn't great when it comes to cleaning the odd small items here and there. As it takes a few hours to heat up the water so I was on the look out for something much smaller for these cleaning jobs.

I also wanted something better quality and I see a lot of people saying Crest is the best, the problem with the best is it's also stupidly expensive. So I was on the look out for an old and broken Crest to get it as cheap as possible, this was actually advertised as 'untested' but that's usually code for broken.
 

 

The first problem I noticed right away was that the tank was no longer properly attached to the chassis. Originally it was attached with a clear silicone sealant. I bought a tube from amazon and reattached it.

 

Leaving that a few days to dry and then filling the tank (never run these dry) it powered on and the heater works but turning the right knob to start the cleaner did nothing.

 

 

 

 

With the board out there isn't too much going on with it, it's a lot more basic than newer Crest models. I think this one is around 20 years old, but basic is good as there's less to go wrong. 

 

At first I thought the IRG4BC30 transistors were bad as neither of my testers knew what to make of them and said they were two capacitors. I ordered some new ones from ebay but those tested the same so that wasn't the issue.

 

After digging a bit deeper I found that the resistor at R1 (10K) was open, it's a wire wound 2W resistor, luckily ebay to the rescue again as one seller had a perfect replacement.

 

 

I am not actually sure if it's 1W or 2W as the original isn't marked and the replacement didn't say either but the original is the exact same size as the new one and it works now so that's good enough for me.

 

Repair complete. 

Ghosts n Goblins (Bootleg) repair

 This Ghosts n Goblins bootleg just sat on a screen of garbage and did nothing.

I eventually found a 74LS74 with weak signals on the top board near the ribbon cable. Replacing the logic chip allowed it to boot and the sound worked but the sprites were messed up (which I forgot to photograph).

I traced this down to a 2114 ram on the bottom board using the piggyback trick (placing a good chip on top of the suspect one).

 

 

Someone had cut pin 18 and then resoldered it, I guess looking for a different bad ram but now this one is bad. Once replaced that fixed all the issues apart from one.

 

The last issue to resolve is that the board is an amputee, with only two and a half feet.

 

 

That's better.

Captain America and the Avengers PCB repair

Captain America and the Avengers by Data East, this came in for repair as it was completely dead. While probing around it briefly displayed an error message but then went back to a black screen. This gave me some hope because at least the custom cpu wasn't dead but there are a lot of custom chips.

After heating up it seemed to show a bit more life than it would from cold, cranking the 5V also helped and going high enough it would actually boot. Then as it heated up I was able to lower the voltage a bit but never lower than 5.3V which is still too high for continuous use.

I decided to let it cool down and then run it at 5v while heating small areas of the board with my hot air station (low heat) until it spring to life, to narrow down the area and eventually the chip. I got to the custom chip '75', which is used for I/O (controls) and security and it fired right up.

Usually the repair attempt would end here but thanks to a kind member of the community that had a scrap Fighter's History board I was able to try the '75' chip off their board. At least according to mame source it is 75 but the markings have been sanded off. Also looking at other Fighter's History board pictures online it's possible it could be a 104 chip instead.

 

The bad 75 chip removed and new unknown number unknown working condition chip fitted.

 

With the 5v line set to exactly 5v I fire it up and....

 

 

 

Success!

Donkey Kong pcb repairs

This is actually two different Donkey Kong boards but I'll post them both here. The first worked but had a really nasty sounding jump sound.

Eventually tracked this down to an open capacitor (C24)

 
A low voltage cap with no physical damage, you don't see these going open very often.

That fixed the jump sound.

Now the second board has a high score saving kit which gave a DMA and NMI interrupt BAD at startup and if I continued it was missing sprites.

 

I expected a bad D8257C DMA controller but after replacing it nothing changed, I eventually found a bad 74LS138 @ 1C

 Confirmed bad out of circuit.

 

 Socket and new chip fitted.

 

  

 

Now boots with sprites. That's it for now but I might have to revist this one as I noticed a small area of garbage at the top of the screen while playing.

RGB-Pi JAMMA adapter repair

This RGB-Pi Jamma adapter with raspberry pi 3+ was completely dead. There's a helpful repair wiki that suggested it was most likely one or both of the I/O controller chips MCP23017 causing the issue.

This is because when the adapter is plugged in upside down it sends 12v where 12v should not be and frys the chips. Checking with a multi meter player 2 button 2 was reading open.

I had to order the very tiny chips from mouser and wait a week for them to arrive.

The Pi faces down, so no wonder these get plugged in upside down.

 

 Bad chip removed and new one fitted.

 

 

I had to dust off the hot air station for this repair as the chip has a ground pad on the bottom of it, making it impossible to remove with just a soldering iron.

 

Repair complete.

WWF Wrestlefest repair

This WWF Wrestlefest board worked fine apart from vertical lines across the screen.

I went down the rabbit hole with this one first thinking it was most likely one of the surface mount custom chips as there isn't too much else on these boards. I fixed a couple of loose pins and took off the TJ-003 custom chip as it was so badly fitted at the factory that the top row of pins were almost touching the wrong pads by less than 1mm.

This made no difference though, I then went on to use a couple of different community made test roms that test the rams but these all passed. The problem with these test roms is they tell you they're testing background / sprite etc rams but not the locations and more importantly the ones they don't check.

Turns out they don't check IC24, 26 and 27, I guess as they don't have direct access to them from the cpu and as these were the main rams I suspected of being faulty I decided to just remove and test them.

Luckily the first one I removed (IC24) turned out to be the bad one, a standard 6116 skinny type. I fitted a socket and a new old stock ram and it's back up and running as noraml.

 

Bad Ram

 

New ram fitted and TJ-003 cleaned up

 

 

 

 

Repair complete.

Virtual Boy Blockbuster case foam replacement

I am not sure how many people in Europe own a Virtual Boy let alone a Virtual Boy in a Blockbuster rental case. But if such a person does exist they'll most likely need to replace the foam in their case. As the original foam disintegrates over time and makes a nasty mess every time you open the case. A good precut replacement is available from an american seller but it's over $100 before shipping.

So I went looking for another option, turns out there's a listing on amazon with the perfect sized pre-cut foam. I bought two 50mm sheets and glued them together with spray glue, this was to give me the option of having some stuff raised so it's not all at the very bottom of the case and it keeps it very close height to the original foam.

 Here's how it turned out.

 

I still need to replace the top part and I put a layer on the bottom so the larger parts like the headset and controller aren't directly touching the bottom of the case, for this I used some of these foam sheets from aliexpress.