Apple iigs power supply problem

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I've got an Apple iigs power supply Model number 699-0126. The voltages coming out of it are low. I have two others which are completely non functional. I suppose I might be able to use some parts from those to fix this one but I don't know what parts commonly fail on these particular power supplies.

Any ideas?

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Re: Apple iigs power supply problem

Visually inspect all the capacitors in the power supply whether there are any bulges on the top cap of those. You can also measure the voltages just after the transformer to be able to isolate the problem a bit. And be careful, when working the PSU.

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Re: Apple iigs power supply problem

I have visually inspected the whole thing and found nothing out of the ordinary. As for measuring the voltages just after the transformer, I don't know exactly where they are or what the voltages are supposed to be. I am also assuming that if there are voltages right after the transformer, then we're measuring AC and not DC.

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Re: Apple iigs power supply problem

insanitor wrote:

I have visually inspected the whole thing and found nothing out of the ordinary. As for measuring the voltages just after the transformer, I don't know exactly where they are or what the voltages are supposed to be. I am also assuming that if there are voltages right after the transformer, then we're measuring AC and not DC.

Yes, you're right, it's still AC. Disregard that advice.

Capacitors may still be ailing even though they appear ok.

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Re: Apple iigs power supply problem

Well, replacing them all would cost a lot and would be time consuming and even after that, there's no guarantee that doing so would fix the problem. This is why I asked for individual components to test in this unit which commonly fail. Parts on this model that commonly fail. I mean, testing a particular voltage regulator for instance. Perhaps a resistor? Diode?

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Re: Apple iigs power supply problem

Hello insanitor,
i´m just now at the moment making "basic pages" to the topic.
just view the thread:
http://www.applefritter.com/content/any-picture-inside-view-old-powersupply-silver-aluminium-case
this pages will start with the former Apple II powersupplies and then in later part also
handle the powersupplies from thirdparty manufacturers and later powersupply models from Apple III
and IIGS too....
so maybe´it´s a good idea to follow up the pages while they are made and search for explenations and
info´s at that pages, while they are currently created...

sincerely
speedyG

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Re: Apple iigs power supply problem

Replaced all electrolytic radial lead capacitors except three. No change. Replaced a coil with a magnet in the middle. No change. Maybe my problem is that I am testing the power supply without a load.

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Re: Apple iigs power supply problem

Hey!

Did the software arrive yet?

Steven Smile

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Re: Apple iigs power supply problem

Hello insanitor,
ALL switching powersupplies must be tested with some kind of load !
I have for example a old damaged 3 1/2 inch harddisk ( with damaged
read/write head but intact electronic PCB ) for such puposes
which i connect to testing supplies..... this guarantees load at
+5 Volt and at +12 Volt. Powersupplies expect at least at that traces
some kind of load at minimum of 300 to 400 mA.
sincerely
speedyG

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Re: Apple iigs power supply problem

speedyG wrote:

Hello insanitor,
Powersupplies expect at least at that traces
some kind of load at minimum of 300 to 400 mA.
sincerely
speedyG

Only poorly designed PSUs need such loading...

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Re: Apple iigs power supply problem

georgel wrote:
speedyG wrote:

Hello insanitor,
Powersupplies expect at least at that traces
some kind of load at minimum of 300 to 400 mA.
sincerely
speedyG

Only poorly designed PSUs need such loading...

According to whom? Only poorly worded posts don't contribute to anything and waste people's time.... but wait, based on most of your posts you obviously knew this already.

Perhaps the manufacturers should all use the switching power supplies you designed since I'm sure they would not be so poorly designed.
Zan

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Re: Apple iigs power supply problem

Hey, when did I give you guys the permission to hijack my thread? Smile Fine. I will participate as being one of the hijackers.

Steven: Yes, the software arrived. I am extremely grateful. The 3.5" disk had a bent dust shield but I think I have bent it enough so that I doubt it would cause a problem with the A9M0106 or the Unidisk 3.5 drives. Now I have to wait until someone sells an Applied Engineering Datalink 2400 baud modem. Not only that, but the modem along with that RJ11 dongle with the two RJ11 female jacks on one side and the connector that connects to the modem on the other side. I would prefer to buy one which originally came with the Dataterm and Online 64 software version 2.5, as I am not 100% sure that the ROM on the modem would have a version that is compatible. It might be a problem if the ROM is only capable at running Dataterm and Online 64 version 2.0 and nothing higher than that. I just don't know enough about these modems.

Speedy: If I do not connect a load to the Power Supply, would it really make this much of a difference in the voltages? I am getting +3.48 - 3.6 volts on the Orange wire, +7.8 volts on the yellow wire, -9.98 volts on the green wire, and -4.68 volts on the blue wire.

Can you explain to me why these voltages could be so strange just because there isn't a load?

Georgel my friend... As far as I know: Pretty much any power supply for a PC needs a load just for the voltages to come out! That means Antec, Enermax and OCZ... If not, then you get really bad volts last time I tried, I got 0. Tell me what that means if your assertion about "poorly designed" Power Supplies is correct...

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Re: Apple iigs power supply problem

Hello insanitor,
well at the moment i have not treated the topic in the current page, though you would understand better, if you have read that page up to current status. I´ll try to explain in simple words:

You have at a switching power supply as most important part a transformer between the primary side and the secondary side.

The power inducted to the secondary side is dependent to the amount of current input at the primary side.

If the secondary side is without any kind of load the amount of current ( please recognize the difference to
not be speaking about voltage ! ) running within the coils drop dramatically, so the drag from the primary side will drop too....

This drop of "running current" in the transformer causes a drop of the inductance to the secondary section and therefor resulting to a drop in transmission of power from primary to secondary side.....

In very many ancient switching power supplies there is only very few regulation to the voltages at the secondary power
( they in general only rectify the voltage with a simple powerdiode - then "smothen" the voltage by a kind of "power balancing electrolytic capacitor"
and then filter off the disturbing AC portion of high frequency swing in the top of the DC power with use of a strong filter coil
and then lead that power to a collecting and again smoothening load output electrolytic capacitor.
( this part is explained rater well up till now at the mentioned page )

So because the most supplies from that days have no kind of "powermonitoring" there is no correction in drawing power from the transformer or simulation of load and therefor due to reduced transmission of power the voltages in all rails will perform a kind of "breakdown" causing drops of the voltage up to 30 % to 40 %.

Reading the mentioned page and keeping along with it in the next days, you will recognize this part of the topic to be close related to the topic of feedback between secondary stage of such powersupplies to the primary stage. You will recognize that this topic was saved because of this reason to the now starting part related to the feedback-topic.

sincerely
speedyG

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Re: Apple iigs power supply problem

Speedy: I have been reading your page. I understand what you mean by "secondary" and "primary" stages of the power supply.

But some things don't make sense to me from your reply. PLEASE FORGIVE me if these seem like stupid questions as my knowledge of electronics does not match yours or probably everyone else in this forum.

1). Why would there be any loss of induction at the secondary side if the current/inductance is being taken care of from the primary side? The only reason I can think of for the inductors on the secondary side are for keeping the current flowing at a more constant rate at the secondary side.

2). You said, "there is only very few regulation to the voltages at the secondary power". But in your schematics, and what I have seen on my power supply, there are at least two voltage regulators on the secondary side. Also on your schematics, there is one Zener Diode in there. I have never heard of a "power diode". I have heard of a "Output Transistor" but I have never heard of a "Power Diode". If we are talking about diodes on the secondary side, I believe that they are for preventing short circuits (you call them shortcuts).

3). I have not taken any current readings, but voltage wise, the power coming out of the power supply has no fluctuation of voltages. I suppose that they are also taken care of by the Electrolytic Capacitors which are supposed to smooth out voltages.

4). Why is there any "smoothening load output electrolytic capacitor" or a filtering of "disturbing AC portion of high frequency swing" on the secondary side when on your schematics there is a "filter stage" on the primary side?

5). When you say, "transmission of power the voltages in all rails will perform a kind of "breakdown" does this have anything to do with the reverse breakdown voltage of that zener diode in there?

Again, sorry for my dumb questions. Please forgive me. I should have allowed Octavio to teach me this stuff.

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Re: Apple iigs power supply problem

Hello insanitor,
first of all excuse, but at the moment i´m still writing at the page without use of a dictionary just using kind of terms familiar to me rather more in german language... this is a problem - because quite a bunch of correct terms in english should have been better translated by use of dictionary....and text is still "draft"

to the first question:
like in any transformer you may compare the power transmitted from primary side to the secondary side comparable to
similar effect like in electromagnetic magnet.... if you put in more electrical power ( either voltage or current )
at the magnet the power of the magnet will raise - the less power you input the less magnetism will be result....
similar effect is valid to power transmission within a transformer..... less input at primary side ( by voltage, current or frequency ) the less portion of power will be transmitted to the secondary side....

but not same but similar effect is also valid to the secondary side if there is no "pull or drag" by load...
Less load means less current running in the secondary coil.... if less current is moved in the coil then also less of the magnetic field power is taken from the primary side.... the less also will be the power itself taken from the primary side.... the magnetic fields at primary side and secondary side are deppendent to each other - that´s the
problem brought to the point...

to the second question:
the powersupply of the IIGS has not been treated at the moment... up till now only the very early powersupplies have been treated and those have been without feedback branch and only the basic power transmission itself has been treated - in that point there is big difference between the powersupply of the IIGS and the Powersupply treated up till now.... but the point explained here in last posting about pull and drag effect and relation between quantity of magnetism initiated at the primary side and amount of magnetism in secondary coils generating power in the coil by induction is still similar and quite close related...

"power diode" is a term used in relation to the quantity of powerdisaption availiable by a component there are components classified as small signal devices and medium power components and power components so diodes used as rectifiers and passing more than 3 to 4 amperes have been classified in former days as power diodes and at zener diodes the classification had been small zener diodes less than 150 milliwatt power disaption and those with more than 500 milliwatt power disaption had been medium power zenerdiodes and those with more than 1,5 Watt power diasaption have been classified as power zenerdiodes....
in my text the term power diodes was not in general use but only restricted to the rectifying diodes that rectified 2,5 Ampere or more in the positive voltage branch....and yep: i use at the moment the term short cut due the the german expression "kurzschluss" which is indeed requiring correction due to the fact that in good english translation by dictionary the correct term should be "short circuit"....

to the third question:
It´s not related to the smothening capacitors.... the power is up to a kind of minimal load dependent to the current flow in the coil.... if there is a load that pulls at least 25% of the possible current and therefor that amount is also running along the inside of the coil the voltage gets independent from the higher amount of current running in the coil..... the effect is only recognizable while the load is less than 25% and gets stronger effective the less current is running inside of the coil...

4rth question -
it seems you have not really been reading the portion of explenation to the function blocks.... at the primary side there is a squarewave put in the coil - this results to pulsing magnetism and to pulsing squrewaves generated at the secondary coils and that pusation must be removed and smothened to get real clean dc at the output of the secondary side. Better not skip that portion ...
it´s important to understand that ( it´s located at and related to the sketches of the wavediagrams marked in red letters from A to F ).....

to question 5
that´s not related in any kind to the zenerdiodes at all...
if you have a voltage at specified amount of current and pull more current power the voltage will "breakdown" because not enough power is delivered fast enough to the place the voltage was taken away from.... the voltage will decrease from a specified value towards 0 Volts..... because no current is availiable fast enough back again at that point....
you might compare that in a kind of way to water in a hose.... if you suck off water to fast the pressure will get lost and measurement of pressure in the hose will drop to no pressure at all...

your not the one to excuse - it´s up to me .... i wanted early feedback to the level the text handles and therfor published a link far before any proofreading of correction occured to the draft text...... at the moment i´m just writing down the text fast to get blocks if info and then as explained in the thread itself, in second attempt when the entire bunch of pages is filled, there will be kind of reorganizsation in the structure ordering that blocks and then there will be a proofreading and check for corrections of terms with use of a dictionary and finally another proof reading for spelling mistakes..... at the moment that text is still rapid draft.... but at the other hand i wanted feedback to recognize if text gets too academic or if the level is understandable also by amateurs...

and as also told - the portion related to special aspects of the powersupplies of the IIGS is also to be treated in later portions of the text.... i´ve recognized 3 different types of powersupplies at the IIGS - seemingly related also to the three revisions of ROMs.... so each of them will be treated while text related to the IIGS supplies will be handled...

speedyG

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Re: Apple iigs power supply problem

Speedy: I think understand everything you said except for this: "at the primary side there is a squarewave put in the coil - this results to pulsing magnetism and to pulsing squrewaves generated at the secondary coils and that pusation must be removed and smothened to get real clean dc at the output of the secondary side."

I think you are describing either an IC or the four diodes required for a bridge rectifier circuit. But according to your schematics, all of these are located in the primary side, not the secondary one.

What am I missing?

I also have another question: You keep mentioning "feedback" and this is related to the IC in some of the schematics.

I discovered that this IC is a quad (quad means four) voltage comparator IC. I am still not entirely sure what they do but if I were to guess, they compare the voltage coming in both the negative voltage and the positive voltage and depending on which is greater, the IC will generate a digital signal, either a 0 or 1 which indicates which polarity has the higher voltage, the - or the +.

I do not understand how the word, "feedback" relates to this concept. If most of the power supply is analog circuitry, then how can the power itself feed back into anything? Moreover, how exactly does a digital signal function in any way with supplying power unless this digital signal is somehow fed into the computer itself and it must be used for (I am guessing) safety reasons. Perhaps a way for the computer to monitor the voltages and cut off the power if the comparator gives an incorrect digital signal?

The ONLY thing I can deduce from the IC itself is that since this is a quad voltage comparator, the four voltage comparators must be related to the four voltages that the power supply supplies. -12, -5, +12, +5.

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Re: Apple iigs power supply problem

Update:

I KNEW the low voltages were a problem on this power supply!

Here's a comparison between this bad power supply and a known good one:

Good power supply:

Connected to iigs: Orange wire +5.01 volts, Yellow wire +11.91 volts, Green wire -11.89 volts, and Blue wire -5.11 volts.

Not connected to a load: Orange wire +5.19 volts, Yellow wire +11.67 volts, Green wire -11.01 volts, and Blue wire -4.81 volts.

Bad power supply:

Connected to iigs: Orange wire +.916 volts, Yellow wire +1.99 volts, Green wire -1.34 volts and Blue wire +.335 volts.

***The Blue wire had a Reverse Polarity!!! I ran the iigs self-test after this and it passed but please tell me that no damage could have occurred to the computer or the very expensive cards I have in it!!!***

Not connected to a load: Orange wire +3.65 volts, Yellow wire +7.9 volts, Green wire -9.91 volts and Blue wire -4.63 volts.

EDIT: I tested all the cards in the system and I found no problem. I also discovered that a particular amusing website works fine with Contiki: http://maddox.xmission.com/ Smile

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Re: Apple iigs power supply problem

insanitor wrote:

Update:

Connected to iigs: Orange wire +5.01 volts, Yellow wire +11.91 volts, Green wire -11.89 volts, and Blue wire -5.11 volts.

Not connected to a load: Orange wire +5.19 volts, Yellow wire +11.67 volts, Green wire -11.01 volts, and Blue wire -4.81 volts.

A decently designed PSU Wink

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Re: Apple iigs power supply problem

georgel wrote:
insanitor wrote:

Update:

Connected to iigs: Orange wire +5.01 volts, Yellow wire +11.91 volts, Green wire -11.89 volts, and Blue wire -5.11 volts.

Not connected to a load: Orange wire +5.19 volts, Yellow wire +11.67 volts, Green wire -11.01 volts, and Blue wire -4.81 volts.

A decently designed PSU Wink

Not sure about that. I've got three busted ones. That was out of the six that I originally had. One of them had a bulging capacitor so I replaced it with one from Digi-Key. Then I sold that system.

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Re: Apple iigs power supply problem

Hello insanitor,

in the meantime i´m now starting the second page about the feedback section.
The most interesting thing you will look for is at the moment the second circuitplan at that page:
http://www.appleii-box.de/appleboxallabotpowersupplies2.htm
It´s the circuitplan of the powersupply basicly used in the Apple IIGS.

sincerely
speedyG

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Re: Apple iigs power supply problem

I am not sure that the second diagram is the schematic for my power supply because it does not contain the symbol for the IC chip (The voltage comparator).

It does seem that it matches my power supply better because it has the four diodes for the bridge rectifier.

While you are explaining quite a bit on how the power supply works, I can't see anything on your web pages that describes how to test the components or which components on the power supply typically fail or which typical parts should be replaced when we see the power supply behave a certain way.

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Re: Apple iigs power supply problem

Hello insanitor,
because the pages are not the answer to ONE specific question, but instead treat the entire topic,
i walk along step by step..... first explaining general topics related to the stuff and then
focusing spot after spot to details.... at the moment i´m treating the feedback paths, what they are for,
how they work and how to identify different kinds of feedback....
the part related to typical mistakes and typical repair is in general reserved for page four.....
though in several points i - while focusing to specific details - also treat typical damages
related to the specific detail spotted out at the moment (like in small parts at page one)...

... and as also explained there are 3 versions of the IIGS supply.... this circuitplan is the one with most
common use of the components and distributed in general with ROM1 version IIGS.

I´m still making drawings for explenation and taking closeup pictures for details of the pages....
....so please don´t be disappointed, if i keep up track with the order of my pages and
keep some patience with the creation of the further pages ..... the more we walk ahead
the more details will be covered including the explenations of how to repair....
up to at least my understanding - it´s recommended to understand
HOW SOMETHING WORKS before making attempts to repair...
this helps to repair correct by not guessing whats going wrong but
instead understanding and identifying what´s really going wrong and causing malfunction...

As just explained this pages shall also be reference in 2 or 3 more years too
and therefor keep trail and order on the entire topic..

sincerely
speedyG

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Re: Apple iigs power supply problem

I understand. I am not disappointed. The thing that I want to know is: on one schematic it says that the input voltage is much higher than 120 volts ac which is what we use over here in the USA. I am assuming that 220 or 240 is used in Germany.

If you use a schematic that uses 220 or 240 volts AC then would there be more variations between the German and American iigs power supplies...?

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Re: Apple iigs power supply problem

Hello insanitor,

its correct thatt here in Europe nearly in all countries 220 Volt to 240 Volt is used while in USA
there is a 110 Volt standard. Second difference is that here we have a standard of 50 Hertz turnover
while in USA its standard for faster 60 Hertz turnover frequency.

But in general it´s possible to change such supplies from 220/240 to 110 Volt
and its more difficult the other way aound from 110 Volt to 220/240 Volt.

The reason is the fact that components limited to 240 Volt will be able to also handle 110 Volt
but components being able to handle 110 Volt might not be able to handle 240 Volt.

And some portion of time will be required to check the results from difference in speed of turnaround frequency too.....

In page 3 i planned to take focus to the primary section of the switching power supplies.
There will we a section focusing about how the switching wave generator is working and
in next focus i want to show how the feedback affects that switching control.

The first part of that page related to the primary section
will treat the mentioned differences between 220/240 Volt and 110 Volt.

sincerely
speedyG

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Re: Apple iigs power supply problem

Quote:

Well, replacing them all would cost a lot and would be time consuming and even after that, there's no guarantee that doing so would fix the problem.

Probably a lot less time and cost than you might expect. I have found people online before who specialize in that sort of thing and are set up with the appropriate tools to be able to perform this "recapping" service at a very reasonable price. Try googling "apple recap" and see what you find. I've sent off all of my Apple IIs and older Macintoshes to have all of their caps (both PSU and motherboard) replaced before they ever showed any signs of trouble, simply on the basis that electrolytic capacitors manufactured in that era are notorious for failing after they reach a certain age. If the PSU still works but your voltages are low, chances are good that an experienced electronics technician can fix you right up with a few capacitors and/or possibly a transformer. (Or do it yourself if you are experienced enough to risk your vintage equipment. Just be sure to clean your contacts carefully and be sure to tinnit afterwards so that they don't oxidize.)

Now, with my IIgs, I chose to replace the power supply with a $30 Mini-ITX one instead. The voltages required for PCs haven't really changed since ever, so this is an easy surgery to do yourself. Basically, just harvest the wiring harness from an old GS power supply, locate a schematic so you can match up the wires, (here's one) solder together, and insulate. I found that a Mini-ITX PSU (unmodified) fits perfectly inside the GS power supply case after you remove the innards. (Use caution when doing so.) I did NOT disassemble the new power supply, but rather just placed the entire thing inside the old shell. Fits perfectly, nice and snug, but not so much that it can't breath.

Also, Instead of simply "shorting" the soft-switch leads, I chose to install a bright red clicky push-button (from Radio Shack) that fit perfectly in the opening from the original power switch. So turning it off and on still pretty much works the same as before and in the same place. (I made sure to make it detachable, too, so I didn't prevent myself from getting to the logic board when necessary.) I also have the Mini-ITX PSU seated in back a ways so as to allow the fan to vent through the opening where the power cord used to go. The power cord plug now connects inside the case, but that's not that big of deal to me, especially since the trade-off is a GS sporting good clean power, that can consume up to 200 watts of power instead of the original 60. Oh, and the PSU's fan has the added bonus of circulating the hot air out of the back of the GS, plus it comes with extra power connectors so I can plug in additional fans or disk drives or whatever else I may want down the road.

Replacing the GS PSU is a good upgrade choice, and should fix your problem, but I still recommend having the motherboard recapped if you can afford being without it for a few weeks. While it's possible that it may never develop an issue, it only takes one venting cap to permanently ruin your logic board, so down the road you might be kicking yourself for not having done so when you had the chance.

FWIW.

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Re: Apple iigs power supply problem

quickthyme wrote:
Quote:

Well, replacing them all would cost a lot and would be time consuming and even after that, there's no guarantee that doing so would fix the problem.

Probably a lot less time and cost than you might expect. I have found people online before who specialize in that sort of thing and are set up with the appropriate tools to be able to perform this "recapping" service at a very reasonable price. Try googling "apple recap" and see what you find. I've sent off all of my Apple IIs and older Macintoshes to have all of their caps (both PSU and motherboard) replaced before they ever showed any signs of trouble, simply on the basis that electrolytic capacitors manufactured in that era are notorious for failing after they reach a certain age. If the PSU still works but your voltages are low, chances are good that an experienced electronics technician can fix you right up with a few capacitors and/or possibly a transformer. (Or do it yourself if you are experienced enough to risk your vintage equipment. Just be sure to clean your contacts carefully and be sure to tinnit afterwards so that they don't oxidize.)

Now, with my IIgs, I chose to replace the power supply with a $30 Mini-ITX one instead. The voltages required for PCs haven't really changed since ever, so this is an easy surgery to do yourself. Basically, just harvest the wiring harness from an old GS power supply, locate a schematic so you can match up the wires, (here's one) solder together, and insulate. I found that a Mini-ITX PSU (unmodified) fits perfectly inside the GS power supply case after you remove the innards. (Use caution when doing so.) I did NOT disassemble the new power supply, but rather just placed the entire thing inside the old shell. Fits perfectly, nice and snug, but not so much that it can't breath.

Also, Instead of simply "shorting" the soft-switch leads, I chose to install a bright red clicky push-button (from Radio Shack) that fit perfectly in the opening from the original power switch. So turning it off and on still pretty much works the same as before and in the same place. (I made sure to make it detachable, too, so I didn't prevent myself from getting to the logic board when necessary.) I also have the Mini-ITX PSU seated in back a ways so as to allow the fan to vent through the opening where the power cord used to go. The power cord plug now connects inside the case, but that's not that big of deal to me, especially since the trade-off is a GS sporting good clean power, that can consume up to 200 watts of power instead of the original 60. Oh, and the PSU's fan has the added bonus of circulating the hot air out of the back of the GS, plus it comes with extra power connectors so I can plug in additional fans or disk drives or whatever else I may want down the road.

Replacing the GS PSU is a good upgrade choice, and should fix your problem, but I still recommend having the motherboard recapped if you can afford being without it for a few weeks. While it's possible that it may never develop an issue, it only takes one venting cap to permanently ruin your logic board, so down the road you might be kicking yourself for not having done so when you had the chance.

FWIW.

I was probably right.

Look at my response where I said this:

"Replaced all electrolytic radial lead capacitors except three. No change."

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Posts: 35
Re: Apple iigs power supply problem

Quote:

Look at my response where I said this:

"Replaced all electrolytic radial lead capacitors except three. No change."

Ah, I saw that, but I must have misread that the other way around somehow, thinking you said you only replaced 3.

The transformer could perhaps also be a cause for the readings you are seeing. The reason I (and others) suspect capacitors, though, is because they often tend to be the first point of failure, especially in older electronics. Resistors, being another analog component, can also sometimes go bad, though it's far less common than these other candidates.

From having discussed with more skilled technicians than myself, my understanding is that certain capacitors in the PSU, when beginning to fail, can exhibit a low voltage symptom, though from what I've heard, it's usually the smaller line filtering ones that go. Therefore, it may go unnoticed for a length of time, in which it eventually causes corrosive damage to both the PSU board and the motherboard. (This is exactly what happened to my original GS some years ago, and is maybe why I'm so capacitor paranoid.)

Regardless, the drop-in Mini-ITX route works great, unless, of course, your efforts are to keep it as close to original as possible. Although, the PSU I chose for mine didn't require any permanent alteration to the GS itself, other than gutting the non-working power supply (which is still replaceable). So, doing that would keep your GS running while you're still working on restoring the other.

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Joined: May 27 2013
Posts: 792
Re: Apple iigs power supply problem

quickthyme wrote:
Quote:

Look at my response where I said this:

"Replaced all electrolytic radial lead capacitors except three. No change."

Ah, I saw that, but I must have misread that the other way around somehow, thinking you said you only replaced 3.

The transformer could perhaps also be a cause for the readings you are seeing. The reason I (and others) suspect capacitors, though, is because they often tend to be the first point of failure, especially in older electronics. Resistors, being another analog component, can also sometimes go bad, though it's far less common than these other candidates.

From having discussed with more skilled technicians than myself, my understanding is that certain capacitors in the PSU, when beginning to fail, can exhibit a low voltage symptom, though from what I've heard, it's usually the smaller line filtering ones that go. Therefore, it may go unnoticed for a length of time, in which it eventually causes corrosive damage to both the PSU board and the motherboard. (This is exactly what happened to my original GS some years ago, and is maybe why I'm so capacitor paranoid.)

Regardless, the drop-in Mini-ITX route works great, unless, of course, your efforts are to keep it as close to original as possible. Although, the PSU I chose for mine didn't require any permanent alteration to the GS itself, other than gutting the non-working power supply (which is still replaceable). So, doing that would keep your GS running while you're still working on restoring the other.

Well, you are probably right. Capacitors are strange things in that they can dry up inside which would show no leakage or bulging tops. Yet because of this, their capacity to hold a charge is not close to what it should be. The thing is, I replaced a lot of them and there was no change. That means that those which I changed were fine. So I wasted my money which was precisely what I did not want to do.

I am not looking to replace the power supply at this time because I have already done so. When I get my Apple iigs running, I will install a Buggie power supply and that's the end of it. Smile

Still, I am VERY curious about why this one is having these issues.

On this power supply I changed all the capacitors inside except the smallest one and the two biggest ones. Concerning the transformer, I have no spares.

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Re: Apple iigs power supply problem

UPDATE:

Talk about making bad choices!!!

I did not know that one of my Multimeters had a capacitor testing function. So I thought to myself, "why not mess around with it?"

I tested the remaining three Electrolytic capacitors.

There are the two big ones, which are 100 microfarads at 200 volts. One of them measured 97 microfarads, the other measured 101 microfarads. I am assuming that these readings are within tolerance.

THEN...

I measured the little guy. The smallest capacitor in this thing. It is a 1 microfarad capacitor, the ONLY one in there.

It was bad. Measuring in only Nanofarads... Way too small.

So, I replaced it.

Now, I am not saying that this power supply is working. I have not yet tested it. If there is something blowing out this capacitor, I do not want that to happen again. It's not like I have a million 1 microfarad capacitors laying around my workshop...

Speedy... Can you pull up the schematic of this power supply and tell me what this might possibly mean? What may have caused this capacitor to go bad and what other components should I check now that we finally have a clue as to what happened to this power supply?

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Posts: 2376
Re: Apple iigs power supply problem

Hello insanitor,
due to the fact of several variations of the IIGS powersupply,
i´d prefer to focus on the correct version.
Please take several pictures from vertical top component side and at least one good large picture from solderingside.
The soldering side shall display in good contrast the entire PCB and it´s traces and be that large
to enable me to zoom in with photoshop ( best a resolution of approx. 2000 x 4000 pixels )
If you place here links to such pictures i will be able to detect which kind of version we are talking about.
Most IIGS supplies also have a "daughterboard" included that contains parts of the feedbacksection...
i´d need at least also from each side of the daughterbord a close picture.
sincerely speedyG

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Re: Apple iigs power supply problem

All right. I put the pics on Dropbox.

https://dl.dropboxusercontent.com/u/103911/PSU.zip

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Posts: 2376
Re: Apple iigs power supply problem

Hello insanitor,
well i´ve inspected the pictures.... thanks a lot they are all well usable....
before getting into the details there are still some areas undetected.....
I´ve taken the total view from your picture from top of the supply and marked some areas and components...:

The components are marked by red shading, number and line to component.
Allthough i´m rather sure about some of the components i´d prefer to get a confirmation about some details:

So if you can read any kind of markings on that components please add a list by
using the same numbers
followed by the reading of that markings....
2 marks an undetected area below the heatsink - if it is possible please try to take a picture
that displays the components below and hidden by the sink ....
this is also valid to the sinks at components 4 and 5.
the electrolytic capacitor at 15 : i´d need the markings and i need to know if the positiv side ( indicated by +
is direction to top or if it´s the minuspol ( indicated by --sign )
I guess 6,16 and 17 to be regular voltage regulators ... please try to add in list of numbers the typmarking
4 and 5 are for sure rectifier diodes - if possible add to list of numbers the typ of component if possible or any kind of marking
3,9,12 and 13 are either rectifying diodes or zener diodes.... please add to list of numbers
any kind of markings which are readable....
same is valid to the transistors.... i guess one of them to be in fact an IC ( TL431 ... maybe 14 ).

If possible add link to pictures of components below sink here
and add listing of numbered components and identified markings here by posting.
At the moment i can state that the PSU had severe problems with heat in the area of the components
numbered from 7 to 13 ( indicated by change of color of PCB ).... this indicates that in this feedback
and driving area of the primary section there might still be a remaining unsolved problem.
If you can turnback with the answers to my questions i hope i will be able to post a detailed commenting
with hints what shall be examined in the night from friday to saturday so you might checkout items in the
weekend.

sincerely speedyG

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the second part includes less friends but a lot more joy on life....

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Re: Apple iigs power supply problem

Object connected to #1 says,
9202 M<--Logo for Motorola
MJE
18006

#7 Transistor says,
~136 "~"<-- Note: two tildes, one on top of the other, is the company logo.
~PN
2222A

#8 Transistor says,
~142
~PN
2907A

Components hidden below #2... A ceramic capacitor that says,
103M
25U

Another ceramic capacitor that says,
221K
1KV

A Green object that seems to be a resistor which says,
2W
470Ω5%

Something which appears to be a diode, it is a white object which has a spherical shape and all I could read on it was, "EPH BY".

The diode you marked as #3 has almost no markings at all. All that I could read on it was the number 7.

#7 and #10 transistors are identical.

#8 and #11 transistors are identical.

#9 diode says,
400
1206

#12 and #13 diodes appear to be the same. I could not read all the letters but it looks like they say:
N493
G115

#16 is a voltage regulator made by the same company that made the transistors. It says,
17BR
LM7905CT

#17 is another voltage regulator made by the same company that made the transistors. It says,
9136
LM7912CT

Writing on #6 component has faded too much for identification.

#15 has no polarity. It is a resistor that says,
22Ω5%
2W

#14 and #11 transistors are identical.

Item connected to #5 says,
91 36
B745
Company logo for Motorola-->MK A" There are no components below the #5 heatsink.

Item connected to #4 heatsink is a diode that says, "9150 G18" The anode of the diode appears to be connected to a magnet which is then soldered to the board. Also under #4 heatsink are electrolytic capacitors which I replaced. These are 330µf @ 25v and 470µf @ 16v.