Gauck 10529c Comparator

I just received this today from the states.

It's a logic comparator much like the one made by HP for testing logic (TTL) chips in circuit, unlike the HP version this will test 18 and 20 pin TTLs or at least it will once I've built it.

I recommend picking one of these up if you do any repairs on electronics with through hole TTL as it's a real time saver. It basically compares the chip on the board with a known good one and compares the outputs, a difference is indicated by an led.

Check out this thread on the KLOV forums if you'd like to order one or need extra cards for your HP comparator as these new ones are compatible.

This is what it will look like once it's done (hopefully).

Toei GM-140TV Caplist / Map

Just a quick one, I recapped a Toei GM-140TV black and white 14" monitor chassis today from a Space Invaders cocktail cabinet. I decided to make a caplist / map since it doesn't look like anyone else has made one.

Mario Bros PCB Repair

I bought this board on ebay as untested and missing a potentiometer. Pots getting broken off of these early Nintendo boards seems to be a common problem.

First thing to do is find a suitable replacement as it's used for horizontal video placement, Bob Roberts sells nice replacements but I don't believe he ships outside the US anymore.

Finding 30K pots the right size isn't easy so I went for a 50k instead, I found some on ebay that looked more or less the right size.

After removing the unwanted bracket and bending the center pin to shape it fit nicely. 

 Now to power it up

 The title screen logo, character,enemy and pipe sprites were all missing.

Now I cheated a bit here as a quick google brings up quite a few posts and even a repair log with this exact issue. Channelmaniac's repair log was very helpful, I desoldered the Z80 DMA and ordered some off ebay.

 Soldered in a socket and fitted one of the Z80 DMAs from ebay and...

All the missing sprites returned.

Mega Drive (Radica)

Next up one of those cheap clone TV plug and play devices that uses composite video and runs off of 4x AA batteries. This is a Mega Drive (Genesis) version rather than the more common NES / Famicom / Arcade versions. The sound emulation on this thing will make your ears bleed but the controller is nice and clicky, I'd go as far as saying it's better than the original Mega Drive controller.

Usually I wouldn't bother fixing these things but it was a such a minor fault. The power button was broken but if held in it would work. Ten replacement switches were 99p from China including postage so why not.

 Power switch replaced, now fully working.

Fake chips (6532AP)

The 6532AP RAM I/O chip in my Fluke 8080 pod failed and finding a replacement isn't easy as they've been out of production for years. I would borrow one from an Atari 2600 but those aren't the A or AP (2mhz) version required for the pod.

Buying anything from China is risky but usually what you get is used pulls cleaned up and sold as new old stock, I don't mind this if the chip actually works and it is cheap enough. In this case the chip was fake, what they obviously did is take any old chip with the same number of pins / package and print what ever they like on it.

 The chip they showed in the auction looks legit

 However this is what I actually received.

Huge shock it didn't work. I took another gamble and ordered some from utsource in Hong Kong this time, their feedback wasn't quite as bad as the other sellers and they looked to sell pulls rather than fakes. This paid off as the five I received from utsource all worked. 

In future I think I'll bite the bullet and buy locally though, even if they do want £11 a chip!

Amstrad CPC 464 repair

I bought this CPC computer in a job lot a while ago but only just got around to looking at it. The main reason I dug it out was to play with my new toy, a ABI Chipmaster Compact not to be confused with the newer but pretty much the same Professional model. This thing will test TTL logic, the majority of old RAM chips and certain CPUs, very handy.

First thing I had to do was find a suitable power brick in my stash, the CPC464 requires 5v 2amp regulated since there's no regulation on motherboard itself.

All I got was a black screen, after inspecting the motherboard I could see the video output socket had some cracked / dry solder joints. Reflowed and retested, still a black screen but the TV was picking up a signal this time. The Z80 cpu is socketed so I pulled it and put it in the chipmaster.

It failed so I replaced the CPU, now I was getting a blue / green screen with vertical lines. I forgot to photograph this but I suspected the ram as it looked to be running as the lines on screen were changing and moving a little.

The first ram I pulled tested fine but the second one did not.

A fully working CPC 464, and now time to test Rainbow Islands as it's the only game I have for it.

PC Engine Core Grafx PAL RF to RGB

I recently picked up two PC Engine consoles one standard white one and this core grafx. The white one only gives a black screen at the moment so I decided to work on this one instead as it worked. Usually this would be a straight forward case of wiring up a composite cable or rewiring the connector to output RGB, but nothing is ever easy. This Core Grafx had been modded to output PAL RF using an aftermarket pcb and rf box.

What a rats nest.

 Removed the RF box and PCB.

I removed some of the solder mask with a fibreglass pen so I can solder the new connector to the pcb at an angle.

Mega Drive 2 video connector fitted.

Slightly neater than before, I used the through holes in the pcb to feed the wires through.

I should have used a larger connector but since the original was missing I decided to use this one that I had on hand. I also like the idea of being able to use a standard Mega Drive 2 scart lead and not have to make a custom cable.

I installed a THS7314 video amplifier inside the system which I have covered before so won't go over again.

After I tested that it worked as it should I put it back together and then decided to check if C162 should be populated which I should have done before I put it back together, as it turns out it should be. It was so cleanly removed it didn't occur to me that a cap should be there, but a google search told me that C162 is a 470uf 16 capacitor. 

There wasn't room to install it in it's original position so I hot glued it to the pcb where there was space and ran two wires to the two pads.