Macintosh IIsi computers don't sell for as much as other Macs from the time period. IIsis tend to have motherboard capacitor damage and the power supplies must be recapped urgently. They have medium speed, one slot, and built-in video, so they are sweet little machines if you get them working.
Although I already have too many of this model, I noticed this one on eBay had the ROM in the slot. (Check out the ROM chip labels of LL, ML, MH, and HH -- just like on the early Macintosh II series)
Most IIsi Macs have two ROM chips soldered on the motherboard. This one has these pads unpopulated and a black jumper installed on W1.
I expected this 'early' (January 1991) IIsi would have a 25-MHz rated CPU, as the rumor was that the IIsi was original developed for this speed. But, it has an ordinary 20 MHz rating.
I do have a 25 MHz IIsi, but it's serial number is towards the middle of the production run (March 1992). The conclusion most people have reached is that the IIsi was designed with some speed flexibility in mind if product management wanted, but the only time they went with 25 MHz rated parts was due to supply convenience. Aside: To get the benefit of the faster-rated CPU, you need to upgrade the G1 oscillator from 40 MHz to 50 MHz.
My IIsi with the ROM in the slot does have another oddity. The power LED has three leads instead of two. That means this is a bicolor LED.
There is an unused pin on the speaker harness that, when wired to the unused pin of a 3-lead LED will light it up in another color when the hard drive is active. Below we see red (HD) and green (power) colors at the same time as the hard drive is being used. (This photo is from a different board where I originally applied the modification)
You can get a similar effect of a flashing (normal vs brighter) LED by simply jumping the unused pin on the speaker connector. Basically, you can think of the metal fingers coming off the motherboard as being numbered 1 to 5:
1. Speaker
2. LED green for power
3. LED ground
4. LED red or brighter for hard drive
5. Speaker
On the motherboard, pin 4 for the hard drive LED already has a 150 ohm resistor and a transistor. Therefore, it is safe enough to connect to an LED pin without additional components. Jump 2 and 4 to get a brighter single-color LED when the hard drive is busy.
This IIsi seemed like someone took really good care of it. The case is the least yellowed I have ever seen, and the fan has almost no dust on it. Yet, the battery was replaced in 1995 and the hard drive was upgraded at some point, so it was definitely used rather than sitting in a closet.
The Bad
Despite the love of the original owner, imagine my disappointment when I discovered that not only was there capacitor damage, but that the power supply and motherboard were still juicy. Look below -- it is literally still wet.
Gross.
In the photo below, note the bottom pad of C11. The cut-off capacitor leads are still attached to the pad. The damage you are about to see is not because the pads were torn off during capacitor removal.
Below is not a torn off pad. Instead, it has been eaten away by leaked electrolyte.
Another 'before' example. Perhaps this computer was stored perfectly flat. Maybe it is just the jelly-ness consistency of this formulation of electrolyte. In any case, the electrolyte tended to sit on the pads rather than leak into a wide pool. Happily, this turned out to prevent damage to other components. Wider damage is common with other IIsi Macs I've repaired.
Here is C20 after initial manual cleaning (isopropyl alcohol and toothbrush) and ultrasonic cleaning. The solder mask still needs to be picked at a bit. But, notice the pad has almost entirely been eaten away.
Here's the repair with the help of a squiggle of wire leftover from cutting off a through-hole capacitor. Previous to soldering, I scrapped off the soldermask on the trace going to ground to make a good electrical connection.
Here's an example using a thinner wire soldered directly to the via / hole to replace a broken trace. The pad was intact, so a thinner wire was acceptable in this case.
Here's an example with thicker wires on both terminals attached to a nearby component rather than the traces.
Power Supply
Another area on the IIsi that deters hobbyists is that the power supplies always need an urgent recap. I don't know what went wrong with the suppliers, as plenty of power supplies from the same era are relatively dry.
Earlier, I showed a picture of liquid on the bottom of the power supply. Here are some of the capacitors I pulled from it.
After removing all of the capacitors from the power supply, I ended up soaking the entire board in isopropyl alcohol and scrubbing it with a toothbrush. Despite the grossness, the traces were in good condition and no components appeared damaged.
But, the daughterboard in the power supply is also of common concern. The bottom four/fifths of the board is damp and the chip leads are crusty.
After manual and ultrasonic cleaning, we're making progress. The capacitors were removed prior to cleaning, but we've also lost a tiny resistor in the process.
Poking at the chip, the solder is brittle and crumbly. In fact, a dental pick reveals that many of the pins are loose. This would not operate properly if reinstalled as-is.
Frustratingly, many of the other components on this board suffer from the same thing.
I removed the worst components and cleaned their pads completely with solder wick. Most just needed some flux and reheating with a soldering iron. Below is the final board after resoldering every single pad and replacing the capacitors with aluminum polymer.
I am showing you the final board below because it is not pretty. I checked every connection with a microscope to confirm that each joint is in-fact solid. Don't expect factory-level attractiveness. The power supply is fully restored and works great.
Despite some sadness that a board with a slotted ROM had such capacitor damage, I am happy that another computer has been rescued and is fully functional. Although it can be intimidating to newcomers to deal with so much leakage, it is good to practice on a machine that is relatively less expensive and reasonably capable when restored.
- David
Although I already have too many of this model, I noticed this one on eBay had the ROM in the slot. (Check out the ROM chip labels of LL, ML, MH, and HH -- just like on the early Macintosh II series)
Most IIsi Macs have two ROM chips soldered on the motherboard. This one has these pads unpopulated and a black jumper installed on W1.
I expected this 'early' (January 1991) IIsi would have a 25-MHz rated CPU, as the rumor was that the IIsi was original developed for this speed. But, it has an ordinary 20 MHz rating.
I do have a 25 MHz IIsi, but it's serial number is towards the middle of the production run (March 1992). The conclusion most people have reached is that the IIsi was designed with some speed flexibility in mind if product management wanted, but the only time they went with 25 MHz rated parts was due to supply convenience. Aside: To get the benefit of the faster-rated CPU, you need to upgrade the G1 oscillator from 40 MHz to 50 MHz.
My IIsi with the ROM in the slot does have another oddity. The power LED has three leads instead of two. That means this is a bicolor LED.
There is an unused pin on the speaker harness that, when wired to the unused pin of a 3-lead LED will light it up in another color when the hard drive is active. Below we see red (HD) and green (power) colors at the same time as the hard drive is being used. (This photo is from a different board where I originally applied the modification)
You can get a similar effect of a flashing (normal vs brighter) LED by simply jumping the unused pin on the speaker connector. Basically, you can think of the metal fingers coming off the motherboard as being numbered 1 to 5:
1. Speaker
2. LED green for power
3. LED ground
4. LED red or brighter for hard drive
5. Speaker
On the motherboard, pin 4 for the hard drive LED already has a 150 ohm resistor and a transistor. Therefore, it is safe enough to connect to an LED pin without additional components. Jump 2 and 4 to get a brighter single-color LED when the hard drive is busy.
This IIsi seemed like someone took really good care of it. The case is the least yellowed I have ever seen, and the fan has almost no dust on it. Yet, the battery was replaced in 1995 and the hard drive was upgraded at some point, so it was definitely used rather than sitting in a closet.
The Bad
Despite the love of the original owner, imagine my disappointment when I discovered that not only was there capacitor damage, but that the power supply and motherboard were still juicy. Look below -- it is literally still wet.
Gross.
In the photo below, note the bottom pad of C11. The cut-off capacitor leads are still attached to the pad. The damage you are about to see is not because the pads were torn off during capacitor removal.
Below is not a torn off pad. Instead, it has been eaten away by leaked electrolyte.
Another 'before' example. Perhaps this computer was stored perfectly flat. Maybe it is just the jelly-ness consistency of this formulation of electrolyte. In any case, the electrolyte tended to sit on the pads rather than leak into a wide pool. Happily, this turned out to prevent damage to other components. Wider damage is common with other IIsi Macs I've repaired.
Here is C20 after initial manual cleaning (isopropyl alcohol and toothbrush) and ultrasonic cleaning. The solder mask still needs to be picked at a bit. But, notice the pad has almost entirely been eaten away.
Here's the repair with the help of a squiggle of wire leftover from cutting off a through-hole capacitor. Previous to soldering, I scrapped off the soldermask on the trace going to ground to make a good electrical connection.
Here's an example using a thinner wire soldered directly to the via / hole to replace a broken trace. The pad was intact, so a thinner wire was acceptable in this case.
Here's an example with thicker wires on both terminals attached to a nearby component rather than the traces.
Power Supply
Another area on the IIsi that deters hobbyists is that the power supplies always need an urgent recap. I don't know what went wrong with the suppliers, as plenty of power supplies from the same era are relatively dry.
Earlier, I showed a picture of liquid on the bottom of the power supply. Here are some of the capacitors I pulled from it.
After removing all of the capacitors from the power supply, I ended up soaking the entire board in isopropyl alcohol and scrubbing it with a toothbrush. Despite the grossness, the traces were in good condition and no components appeared damaged.
But, the daughterboard in the power supply is also of common concern. The bottom four/fifths of the board is damp and the chip leads are crusty.
After manual and ultrasonic cleaning, we're making progress. The capacitors were removed prior to cleaning, but we've also lost a tiny resistor in the process.
Poking at the chip, the solder is brittle and crumbly. In fact, a dental pick reveals that many of the pins are loose. This would not operate properly if reinstalled as-is.
Frustratingly, many of the other components on this board suffer from the same thing.
I removed the worst components and cleaned their pads completely with solder wick. Most just needed some flux and reheating with a soldering iron. Below is the final board after resoldering every single pad and replacing the capacitors with aluminum polymer.
I am showing you the final board below because it is not pretty. I checked every connection with a microscope to confirm that each joint is in-fact solid. Don't expect factory-level attractiveness. The power supply is fully restored and works great.
Despite some sadness that a board with a slotted ROM had such capacitor damage, I am happy that another computer has been rescued and is fully functional. Although it can be intimidating to newcomers to deal with so much leakage, it is good to practice on a machine that is relatively less expensive and reasonably capable when restored.
- David
