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Apple IIgs Dyna Comp LR 38879 power supply recap questions....

tblake05

Experienced Member
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Aug 21, 2017
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Popped a rifa last week.

Ordered the "correct" cap kit from console5 for this supply including two rifa's I smoked. Yep I forgot to order the two smaller rifas (A) My bad.

The forward cap in (C) is a 1uf 50v that came in the kit. I also need one for (B) same value. Kit only came with 1. Ok. No big deal. I had a spare in my supply.

Cap (D) is a 470uf 16v. Nothing in the kit close???

Two caps in (E) are the same deal. They are 330uf 35v. Nothing close included in kit.

So as far as being short those 4 values from the kit, they sent extra: 2x 1000uf 10v (which are the correct value for the 3 that are alongside (E), 1x 330uf 25v, and 1x 10uf 25v.

The kit had no instructions, so I don't know if I'm ok to use the ones they sent. I bet not though. I suppose it's possible someone was in this supply before me. Though they all had glue on them still. A check of the schematic would confirm this though I haven't done it yet.

It almost killed me to desolder all those neat yellow elna caps. BUT I'm glad I did because every single one of the caps in this thing were leaking. Not bad, but they were. Hence the dimming power light I had when the drive seeked.

My question is though if anyone experienced this with console5? They've been pretty good in the past. And the sealed bag they sent had my power supply model number on it. I think I'll just order the remaining caps from mouser and call it good. Just more money spent on shipping plus more time.

Thanks!!
 

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these power supplies are easy.. you just need to replace the caps at B and C (3caps) and it will be fine. those are the bottleneck on this psu. nothing wrong with replacing them all but you really didnt need to. If you look onljne lots of folks have Cap kits ( i think cap kits are a bad idea but thats another argument to be had) that have just 2 or 3 caps total for this psu.
 
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Check out the electrolyte under (E) though. All of them in that area were crusty on the bottom when removed.
 
The pictures resolution isnt too sharp so I cant really say for sure. To me it just looks like a black rubber imprint from the capacitor rubber boot. If it was electrolytic crud it would be a brownish yellow. Can you show the bottom of the cap that came from the questionable spots?

Just clean those spots with a cotton bud and isopropyl alcohol before installing a new cap.
 
The pictures resolution isnt too sharp so I cant really say for sure. To me it just looks like a black rubber imprint from the capacitor rubber boot. If it was electrolytic crud it would be a brownish yellow. Can you show the bottom of the cap that came from the questionable spots?

Just clean those spots with a cotton bud and isopropyl alcohol before installing a new cap.
Yes, yellow crusty residue on the bottom of the caps themselves. Just beginning to start.
 
Well then they need to be replaced. Were they stored in an attic or hot area?
Ya. The machine was used at some sort of a machine shop. Then it sat in hot storage for some years before I got it.

Here’s what the bottoms looked like. Not much crust, and still working, but I’m here...
 

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Oh yeah. a hot area will dry out the rubber stops and then thst stuff will just ooze out. Heat is not kind to electrolytics
 
Oh yeah. a hot area will dry out the rubber stops and then thst stuff will just ooze out. Heat is not kind to electrolytics
Is it possible someone switched the top to my power supply? Cause this one is identical to mine but its a LR62786


Plus does anyone have a schematic for this supply? and/or what value is that fuse? I forgot to ohm check it before I left for work today and for some reason, it looked blow to me after the rifas popped. Is that possible? I'd like to get an order placed for the remaining caps before I leave this job and head to my next one. Thanks!

 
There are a few schematics floating around for Dyna Comp power supplies labeled as for the Apple IIe with Apple power supply part numbers that might match or otherwise be of help due to the similarities between the IIe and IIgs. Is there an Apple part number marked on your supply?
 
I just recapped my IIe power supply, DynaComp LR38879 but I only had 3 of the 1000uF 10V, so they recommend getting the LR62786 kit.
Sadly, after the recap its still clicking and flashing the power and board LEDS. Something else must be bad.
 
Dont buy kits.. just buy the caps you need. Kits are a waste of money.

what were the voltage outputs from the psu prior to you recapping it? What made you assume it was a psu issue?
 
Dont buy kits.. just buy the caps you need. Kits are a waste of money.

what were the voltage outputs from the psu prior to you recapping it? What made you assume it was a psu issue?
Same symptoms (flashing power and board LEDs), leaky metal caps, tried a working PSU and it boots fine. With it clicking and flashing the LEDS on the IIe, I didn't leave it on long enough to check voltages.
$12 bucks wasn't too bad for all the caps and the RIFA's, actually..
 
Ok now we are getting somewhere. it works with a different psu. So put the faulty one back in and use this pinout for the apple ii power conector as a reference. Turn on the conouter and take and record voltage readings. Also if you can a good photo of your psu board.
D3ropjHUcAAjKTJ.jpg


Whichever voltages are incorrect or missing will tell us where in the circuit the problem is.
 
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Ok:
Pin 5 = -12.14 Pin 6 = -4.99
Pin 3 = 1.44 Pin 4 = 7.39

The diode marked on the board showed short, but was good when taken out of the circuit - this is the same in the working PS I have.
 

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There are a few schematics floating around for Dyna Comp power supplies labeled as for the Apple IIe with Apple power supply part numbers that might match or otherwise be of help due to the similarities between the IIe and IIgs. Is there an Apple part number marked on your supply?
Hi - the Apple part number is 699-0133.
I found some reverse engineered ones that look pretty good for the DynaComp LR38879.
 
Hi, I just put them up in a .7Z file on my domain - you can just right-click and select Save As - not sure why everything is coming up as 'unsafe' anymore - it's the site of my 30 year old webpage, mostly.. :



Any ideas with my voltages and the pic I put up of my power supply?
I am trying to open the pdfs in this file but they are showing up corrupt. Did you try and open this?

edit: website crashed when making an edit./ I will have to remember what I typed... So I dont like cap kits.. They usually have no instructions and they dont cover all the caps. Its up to the seller to pick and choose what they add.. Cap kits are like a "tune-up" on a car. For the most part the term is make believe. A tune up can be wiper blades and a new alternator belt. Its just easier to source the caps you need yourself.. ITs easy, your smart enough to have written things down so you are more than capable.

Again a blown rifa wont take out the psu... at all. The problem with your board (have worked on a bunch of them) is there is no silk screen. so I am assuming your board was still working when you got into it and made changes. Did you take photos? Without photos and no silkscreen you could have easily reversed a cap polarity. I highly recommend you re-trace your steps. Maybe even undo the changes. However if you dont have photos on polarity.. dont bother that might just get you more lost. We need a schematic to verify the cap polarity. Can you at least make a dot with a marker on each cap you replaced so it will be easier to check?
 
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Ok:
Pin 5 = -12.14 Pin 6 = -4.99
Pin 3 = 1.44 Pin 4 = 7.39

The diode marked on the board showed short, but was good when taken out of the circuit - this is the same in the working PS I have.
Shorted from both anode to cathode and from cathod to anode when you flipped the leads?
 
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