Re: Recapped PowerMac 8100 PSU and now unstable
I took that box cap out and it tested fine. Now, I have removed the blue disc caps and tested them out of circuit with the DMM, and they all test within tolerance for their specified capacitance. They are all far too small to test ESR. I tested the large filter caps, both published at 680µf, both with 0.17 ohm ESR, one 601µf, the other 592µf, so all around good. I also took out and tested the thermistor within the circuit...It appears to be rated for 7 ohm (it is 15SP M007), and tests at 11 ohm.
I can test more ceramics...
LaPorta
Member
Last Activity: 04-23-2021, 07:27 PM
Joined: 03-13-2021
Location: Burlington, CT
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Re: Recapped PowerMac 8100 PSU and now unstable
I’ll do that. One thing also to remember is this problem existed prior to my changing out the caps. The problem existed 20 years ago when I acquired the machine, I just never got around to it till now!Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
So I pulled that cap and some of the blue ones and the other larger gray box one as well. My ESR meter couldn't read them because they are just too low capacitance (0.1µf, etc), but my DMM at least verified their capacitance to be good. As for the high ESR reading, that was in-circuit and it was misreading as the capacitance reading was off as well.
Should I just shotgun replace some of these? I'll keep pulling the filter caps up to and including those around the massive ones.Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
There are a number of ceramics and what look like thermistors in the input section. There is also a board with transistors, etc. on them that is tied into the circuit. The input from the mains is connector J1. The last photo is the actual input board. There are two disc caps on there, they appear to bridge between the hot and neutral to ground, respectively.
The gray box cap, CX1, in line with the connector J1, has a listed value of 0.1µf on its casing, but tests with both my ESR tester and DMM at 0.58µfm with ESR of...Last edited by LaPorta; 03-20-2021, 09:43 PM.Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
I did as you suggested. Both PSUs supply a constant +5V DC to the 5V pin of one of the built-in RAM chips. With the known good PSU, the 5V is constant no matter what time course adjustment. However, with the PSU that is giving me issues, I can detect what appears like a sine-wave interference within the 5V signal becoming noticeable at a scale of 100 ns/division. This is not visible at all on the good PSU. So, I would assume this tiny wave does not interfere with gross function (power on, etc), but at some point causes garbage either...Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
You guys were on point: I changed out that 100µf with one that was closer in spec and the thing now stays on!
However, I discovered something that I did not know previously. I was having issues with the machine locking up, freezing, having bus errors, etc, within a few minutes of it starting up. I thought it was the logic board previously. However, now that I have a spare logic board and power supply to test with, I have discovered that the issue only happens when this power supply is connected. The spare PSU does not...Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
Thanks...how does that help us with this?...Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
Ok so the series determines what the ESR ranges, I got it. Regrettably, I do not have the original parts. I had saved them for a while but no longer.
Would you then suggest similar capacitence/voltage rated parts, but instead of the FR series? I can always order/locally source some to try.
Also: where do I find the ESR on it's dat sheet? I likely chose this part simply because of it's high stated life.Last edited by LaPorta; 03-17-2021, 04:06 AM.Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
Thank you for the reply. Please forgive me, as I do not know the difference between series and would appreciate being tought these differences. What would cause the instability? And, which one is it that is? If you can tell me from the list that I posted, I can figure out which capacitor on the board it was and post the requested photo...and possibly get a new part if required.
EDIT: Is that the 100µf, 50V ones? I can find them this evening per my notes on the board.Last edited by LaPorta; 03-17-2021, 04:01 AM.Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
Attached are the photos. There is the small 120VAC in/out repeater board. The rest of the supply is two main boards at 90 degrees to each other. There are also two small daughter boards, one that had two caps that I replaced (the photo that looks like a cave). The other has what looks like small control circuitry. The undersides of the boards are very clean as well. Again, this worked fine until after the recap. Now it just shuts off after a few minutes....Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
All were replaced - including the large filter ones. Will have to take more photos now to show the whole thing.Leave a comment:
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Re: Recapped PowerMac 8100 PSU and now unstable
Attached are three photos of the supply prior to recapping. They were not the best photos, mostly for my reference while I was working. There is a horizontal board, vertical board, and also a tiny board that is sandwiched in there that I had to remove to replace two or three more.
I'll also attach a list of the caps I used to replace the ones on it with....Leave a comment:
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Recapped PowerMac 8100 PSU and now unstable
Hello everyone,
This is my first thread, and I am new here. I am part of the 68kMLA forum, and I was referred over here by one of the members there who is a member here as well.
I have a power supply from a Power Mac 8100 (Delta Electronics, Model # DPS-225AB Rev: A0, Apple Part Number 614-0040). It worked fine prior but, being close to thirty years old, it was time to recap. I have done a lot of capacitor replacement, but am by no means an expert at all. I looked up the replacement parts and ordered on Mouser. All electrolytics were replaced with same capacitance... -
Re: New Members - please post your introductions here
Hi everyone, my name's John. I was forwarded over here by a current member for help specifically with a Power Mac 8100 power supply (a Delta Electronics model) that I have recapped and am having vexing power issues with. No doubt, due to my large collection of 30 or so Macs, I will be here not too infrequently with questions.
I am from Connecticut and have my collection with me in my home. I really only collect Macs (and just a few Apple IIs). People never used to believe me that I had so many!
I...Leave a comment:
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