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Title: Minor issue after installing new power supply Post by: ahaigh01 on August 12, 2015, 01:26:56 PM I installed the MeanWell T60-C power supply in My EII along with an HxC. It's been working very well. One thing that has changed is when I first turn on the EII there is a new noise (not the typical "pop"). It is a low tone, like a sine wave, that starts very low and begins to rise in pitch. Then it stops after a couple seconds when the boot up starts. I am wondering what is causing it, now that there is the new power supply installed. Or maybe the HxC is causing it, but I am guessing it is the PSU. Anyone know?
Thanks Title: Re: Minor issue after installing new power supply Post by: Gregory on August 12, 2015, 02:12:21 PM That's interesting. I have recently changed the PSU as well (the new PSU is not a Meanwell though) and everything seemed to work great. However, after a couple of weeks I've got exactly the same symptom you're describing.
I was able to fix it by replacing a circuit in IC86 socket on the Digital Board. Actually, I replaced several curcuits on the Digital Board that day (I still have a replacements list if you're interested), but the problem only disappeared after replacing the circuit in IC86. Perhaps you should try to replace this circuit as well - it is inexpensive anyway.. Title: Re: Minor issue after installing new power supply Post by: ahaigh01 on August 12, 2015, 05:07:03 PM Hey Gregory,
How did you happen to know it was IC86 - trial and error? I have some replacement ICs so I tried one. Although it fits the socket it is the wrong type and the boot up stops. Thanks for your input. Title: Re: Minor issue after installing new power supply Post by: ahaigh01 on August 13, 2015, 07:10:27 AM Gregory - I am interested in the replacements list - thanks
Title: Re: Minor issue after installing new power supply Post by: Gregory on August 13, 2015, 07:12:33 AM Please, only replace the circuits of the same type. Otherwise you are at risk to damage your EII. The circuit in the Digital Board socket IC86 is 74LS138.
I was told that this symptom most probably caused by something dealing with reset process. Since I'm not a tech, I decided to just replace several circuits "in question" - and it worked. Title: Re: Minor issue after installing new power supply Post by: Gregory on August 13, 2015, 03:09:15 PM Gregory - I am interested in the replacements list - thanks Sure, I have sent you the list. Title: Re: Minor issue after installing new power supply Post by: ahaigh01 on August 17, 2015, 06:06:41 PM Good news - replacing that IC fixed the problem! Thanks for the great info.
Title: Re: Minor issue after installing new power supply Post by: Gregory on August 22, 2015, 01:39:28 PM I'm glad it fixed the problem!
And I wonder if it's a coincident that this particular circuit failed in two different Emulators after replacing the Power Supplies.. Title: Re: Minor issue after installing new power supply Post by: ahaigh01 on August 24, 2015, 06:52:10 AM It could be. I bought 10 of those ICs so I can replace it again if needed, but I hope it doesn't fail again.
Title: Re: Minor issue after installing new power supply Post by: alka on May 31, 2017, 08:29:03 AM Old post, I know, but I wanted to add on to the notes here in case anyone else experiences this issue. Replacing IC86 did not solve the issue for me. I have had this issue twice before - one fix was to swap the 2 Z80 CPUs. The other was to replace the MC3400P and/or the AD7524 on the Output board.
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