Re: A tale of a chip and a socket
On 04/09/2016 5:29 AM, Noel Chiappa wrote: > From: Torfinn Ingolfsen > Most likely a bad solder joint. That was my first thought, and so I carefully inspected all the pins, but they all looked good to me. But I suppose it might have been something that wasn't visually obvious. Noel If you suspect solder try simply reheating the legs of the suspect chip to see if that cures it. It could also be that the chip is drifting out of tolerance and the clip you put on it added enough extra capacitance (we're talking picofarads here) that it was happy again. The IC socket may add just enough capacitance again to help the chip get back into its operation band. Has anyone else got a similar board and that particular chip has a very small value cap on one or more of its legs? I see this on my 1970s video game boards from time to time - a board from the factory would have an added cap on one chip that isn't shown on the schematics or in my meagre collection of service bulletins for that game. The job was obviously factory as the connection is as clean as all the other connections on the board. Data books don't talk much about this bypass caps issue either, I believe it is part of the 'magic smoke' of TTL logic... John :-#)# -- John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames) www.flippers.com "Old pinballers never die, they just flip out"
Re: A tale of a chip and a socket
> From: Torfinn Ingolfsen > Most likely a bad solder joint. That was my first thought, and so I carefully inspected all the pins, but they all looked good to me. But I suppose it might have been something that wasn't visually obvious. Noel
Re: A tale of a chip and a socket
On Fri, Apr 8, 2016 at 11:19 PM, Noel Chiappa wrote: > So I just had the incredibly amusing experience of managing to repair an > -11/04 CPU by un-soldering a chip, putting in a socket, and putting _the same > chip_ back in that socket! > > Before you go 'WTF?!?!', let me explain what happened. Most likely a bad solder joint. Happens from time to time on 30 years+ old equipment. -- Regards, Torfinn Ingolfsen
A tale of a chip and a socket
So I just had the incredibly amusing experience of managing to repair an -11/04 CPU by un-soldering a chip, putting in a socket, and putting _the same chip_ back in that socket! Before you go 'WTF?!?!', let me explain what happened. The CPU wouldn't run, and in poking around, I stumbled on the cause: all the registers would not 'take' 1's in the 0360 bits. Hmm, 4 contiguous bits - sounds like it might be a bad register file chip. But before I pulled it, I wanted to make sure it wasn't some other part of the data path - Mux, ALU, etc. So I put a DIP clip on the chip, whipped up a 3-instruction 'scope loop that would exercise it, and... while I was looking at it, the problem went away! WTF? So I pull the clip - and the problem comes back. Repeat. Clearly there's a bad connection in the chip, and the pressure of the clip is 'fixing' it. So I pull the chip, put in a socket (I always use sockets on repairs, I'm paranoid I'll overheat the parts - I don't mind living with an potential eventual bad contact from corrosion), and figure what the heck, let me see if fiddling with it fixed the bad connection - and sure enough, it now seems to work! And if it eventually fails, no problem - it's in a socket, I know where to go if the machine stops working, those P3101A's are rare and expensive, etc! :-) Noel