Arcade Collecting > Restorations & repair
I don't believe it, another classic added => Centipede ! FINISHED !!!!
Level42:
Hey Fredster thanks for that info !
I don't guess I can still get those oldy RAMs around here... I think I'm going to have to do a pretty big order with Bob Roberts (Big Blue, trackball parts etc.), the only problem is it's very hard to order from Bob from outside the US. He doesn't accept PayPal or CC, which both are my options for international orders.
Do you think the 6502C from an Atari 800XL will work (just to check)....I got one here. I read the C has one extra pin that should be kept high to enable it. Think that's the only real difference.
Well the easiest thing would be buying your board of course, but something is telling me I ought to try and repair this one. Not for the money really, but, you know, a saved board is another saved board.... :)
I'm pretty good in electronics, but it's not my daytime job to hunt down digital PCBs, but I do want to give it a try. I will definitly need that oscilloscope (wish I had an Atari CAT box :) )
Your knowledge and experience could really help me out Fredster :) ! Until march 28th, I'm really very tied up with other things in my spare time, so it'll take a little while before I start on the Centipede. I also want to finish the Galaxian ASAP. Thanks about the cones Fredster, but I already got some from Luigi, see his kind offer :) But thanks anyway...
I love this forum !!! :cheers: :applaud:
Level42:
So far, I've only checked the voltages on the PCB test points and they seem to be fine. What I did do, was change the plug on the power supply. My power supply is the European version. By changing the plugs, you select the voltage it operates on. It was on 220VAC when I got it. However, in recent years, the mains voltage has been increased to 230VAC on mainland Europe. (UK lowered it from 240VAC to also 230VAC). This to reach one standard voltage within Europe. The result was that some voltages were a bit on the high side (not the regulated one's of course, f.i. the 5V was 5.01 Volts).
So I switched it to the 240V connector and that lowered things a bit.
Still the same thing on screen.....just random characters from the game like centipede parts, spider, mushrooms, shooter etc. and they are standing still. The reset button has no effect (I checked it, the button itself works fine). I removed all socketed chips, and re-inserted them. There have been IC's replaced on the board, I can see that from soldering marks. Solderings look ok generaly. Could there also be problems with the sockets (corrosion ?) the pins on the socketed IC's looked very clean though..
Level42:
OK I did some research about the RAM on the Centipede PCB's. I made a small Excel file that's attached here.
There's something strange about the RAM chip on C8 position. It's mentioned as 82525 or B2525 on the manual but there's a 6560N on my PCB.
I also found another source for those chips: www.arcadechips.com has everything but the 6560N. They have an on-line ordering system, ship international AND accept PayPal.
Price's are right too. They also have 6502 and even Atari's Big Blue.
The Service Manual mentions that the board "shows" any RAM errors with beepcodes (was Atari ahead of it's time or not ? :) ) There's a range from 1 to 10 each indicating for a certain RAM that MAY be bad.
"Any bad RAM must be replaced before the computer can check the other RAMs, as well as continue with the self-test." (Service Manual quote)
Now I don't hear any beeps. In fact, I only hear a scratching sound when powering up the cab when it's been off for a while. If I turn it off and switch it back on again after 10 seconds there's no sound at all...(elco's ?)
I could monitor the sound on the test-points to see if there's any beeps to be heared.
But I think I will order a full set of RAMs anyway...they're cheap enough...
I don't have a logic probe, but I do have an Oszifox. This is a pen-shaped measuring device, that's actualy a tiny osciloscope.
http://www.wittig-technologies.com/english/05_products/01_oszifox/oszifox_01_intro.htm
The bandwidth is only 5 Mhz, but that should be enough for a board running on 2 Mhz. You can connect this to a PC (regretfully not Mac) via RS-232 and run scope software. I didn't do that (yet), there's also a small display on it that shows the waveform etc.
So I poked around with it on the board. Sure enough there's a clock signal and I've checked many pins on RAMs, 6502 and Pokey. All show lines going high/low. So there's definitely life in it :)
I also hooked up my DVM in diode-test (yes I did power down the PCB first :D) and measured to ground all pins of RAMs that are on the board in 2 or more to compare. All the 2101/9101's showed identical values. However, on the 2114's I got different results on some pins...
Pin 13 and 14 show different values between H2 and F2. Could this indicate a bad ram ? The lines on those pins go straight to E2 that is a 74LS245, a bus transmitter/receiver. Here I measure the same "wrong" values on pin 6 and 7 (which is logical of course). So, the 74LS245 could also be bad...any suggestions before I desolder the pins to check this out ?
RayB:
Wow, so much work, $$ and shipping, with no guarantees, when you could just buy a working board.
Level42:
Well, a working PCB would cost me almost $100,- incl. shipping.
The RAM's will be a lot less. I THINK I am on the right track, if so, I would only need a single 2114....at $1,60 (anyone has a spare ?).
In all honesty www.arcadechips.com has a minimum order of $15,- but I will probably throw in a Big Blue anyway and that's $11,- already. Include an extra 2114 and an extra 2101 or two and I'm at the $15,-. Shipping is only $5,- USPS ground (I'm in no rush). So that's about $20,-
Also, there's 2 more reasons to do this:
1) The challenge
2) The fact of saving a Centipede PCB
I know that both will give me a kick IF I get the board back to life :)
Throwing away a PCB that has only 1 bad chip would make me feel bad :D
Indeed, there's no guarantees, but I like to learn ! Maybe I will regret it later, but at least I've tried then...
[Edit] Think about this: I could have bought a completely restored and working Centipede cab for, let's say $1800.- and have it shipped here for another....let's say $400,-
Besides not having the money for that, there's no glory in it.... restoring the game is at least as much fun as playing it...
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