Finished recapping my SPEC 4. It’s all back together and working great. Here’s how it went for me:
Standard Disclaimer: The attached parts list represents a snapshot in time. It's the right list for my unit, yours may be slightly different. Mouser part numbers change and they run out of stock so you may need to make some substitutions. The list should also be inspected by one of the AK gurus (you know who you are) to ensure it meets with their approval. The mods are more than welcome to publish it in the AK recap database if approved by one of the AK gurus. This isn’t intended to be a how-to guide on recapping a SPEC 4. It simply represents how I approached it on my SPEC 4. If this helps others, great. If you screw something up, I don’t have the skills to help you troubleshoot it. If you see a mistake here, let me know.
STOP! Before you do anything, familiarize yourself with the diode pack in the following picture. HEED THIS WARNING: if you bend the leads on this device at all, they will probably break off right where they exit the case. These particular components are no longer manufactured! YOU HAVE BEEN WARNED!
One more thing: there are voltages inside this unit that can easily kill you so PAY ATTENTION TO WHAT YOU ARE DOING! Do you have a dish ready to hold all of the screws so you don’t lose any?
Power Supply Caps: Get the top and bottom covers off. Before you touch anything, measure the voltage across the big caps to verify that they are discharged (you should do this after every every time you apply power throughout the process). It’s easier to undo the big power supply cap clamps such that you remove two at a time. Make sure to take a picture or write down the orientation of the caps with regard to polarity before you remove the originals. You may need to open up the wire terminals to accept larger screws, depends on the brand of caps you buy. If you do need to open them up, whether you use a drill or a rat-tail file, use a towel or something to keep the filings from falling inside where you might not find them until they make their presence known by shorting something. Once you get the new ones in, check them 10 times against your diagram or photo just to make sure you put them in the right way. Plug your SPEC 4 into a dim bulb tester with a 100 watt bulb in it and power it up to make sure everything is normal. (The first time you do this it will FREAK you out because it needs to draw so much power that the soft start relays won’t completely engage and you will hear a loud buzzing from them for a few seconds until the caps charge. Remain calm for a few seconds.) If everything seems normal, power it off, unplug it and proceed to the next part. If things aren’t right, recheck your work and/or get help.
Meter Board: Disassemble the front panel until you can get at the meter board. Cover your big beautiful meters with a towel so they don’t get scratched! Proceed to recap. On my SPEC 4, C1 and C11 were different as indicated in my parts list. C16 was in the parts list and in the schematic but not shown on the parts layout diagram. My rule is: if it was working satisfactorily before you started, put the same value of parts back in that you remove as opposed to changing them to what you see on the parts list or schematic. The only exception to this is if someone has been in there before you and there is an obvious hack-job. Please also note that on the parts layout I have, C13 is shown in the INCORRECT orientation. Verify with the schematic!
Once I finished the recap of the meter board, I very carefully checked operation on the dim bulb tester again before I went to the next stage. I think it’s good practice to test after making a change because it makes it easier to troubleshoot if you do make a mistake. If everything is ok, it’s probably a great time to Faderlube the front panel volume pots and Deoxit the power switch. Reassemble the front except for the aluminum panel and rack handles.
Amplifier Boards: Take a picture or make a drawing of what connectors go where and what color wires go where so you can put them all back in the right place later. Do one amp board at a time. Disconnect the 4 wires and 2 connectors. Carefully remove the amp module from the chassis. Mark the output transistors so you will know where to put them back. Unscrew each output transistor and pull them out of the sockets, and off of the heat sink. CAREFULLY remove the mica washer under each output transistor. Remove the screws holding the board onto the heat sink brackets. CAREFULLY remove the single screw holding the diode pack in place (DON’T BEND THE LEADS). CAREFULLY remove the power amp board from the heat sink and set it aside. Remove the 2 steel heat sink mounting brackets. Clean all of the old heat sink grease off of the transistors, mica washers (careful, they are brittle) and heat sink. You may also want to wash the heat sink at this point. Proceed to recap the power amp board. Be careful not to change the settings of any of the variable resistors. Replace VR1 and VR2. Reassemble the power amp board back onto the heat sink (once again being very careful of the diode pack). Apply fresh heat sink grease to the bottom of the output transistors. Apply the mica washers onto the bottom of the output transistors then apply heat sink grease to the clean side of the mica washers. Place the output transistors back in the sockets and screw them in place. Do it all over again with the second amplifier board. Carefully reassemble the amplifier modules back into the chassis and reconnect everything as per the drawing or photos you made earlier.
Testing and Adjustment: Go find a long skinny flat blade screwdriver that you can use to adjust VR1 and VR2. Cover the metal shaft with heat shrink tubing so you don’t accidentally short something in the process. Connect the SPEC 4 to your dim bulb tester (nothing else connected) and turn it on. The bulb should be bright and then dim, and in 10 or 20 seconds, you should hear the protection relay click. If not, troubleshoot and/or get help. If all is well, adjust VR1 to obtain zero volts between + and – of the speaker terminals. Adjust VR2 to get as low a reading as possible (close to zero volts) between terminal 26 and terminal 16 (see the service manual for location and USE CLIP LEADS ON YOUR VOLT METER SO YOU DON’T SHORT SOMETHING ACCADENTALLY). Adjust VR1 and VR2 on the other power amp board. If you can’t get both settings close to zero volts, you have a problem (troubleshoot and/or get help). If all is well, power off. Plug into mains, power on and perform the adjustments for DC Balance and Idle Current as shown in the service manual.
Reassemble and enjoy!
Hey wait, you didn’t adjust the Power Limiter or Meter Amplifier. You’re right. I didn’t move the pots while recapping and didn’t change any parts that would require them to be adjusted. Plus, I don’t have a 4 ohm dummy load so, I left well enough alone.
As I write this, my SPEC 4 has been running for about 4 hours with no issues and it sounds awesome!
Standard Disclaimer: The attached parts list represents a snapshot in time. It's the right list for my unit, yours may be slightly different. Mouser part numbers change and they run out of stock so you may need to make some substitutions. The list should also be inspected by one of the AK gurus (you know who you are) to ensure it meets with their approval. The mods are more than welcome to publish it in the AK recap database if approved by one of the AK gurus. This isn’t intended to be a how-to guide on recapping a SPEC 4. It simply represents how I approached it on my SPEC 4. If this helps others, great. If you screw something up, I don’t have the skills to help you troubleshoot it. If you see a mistake here, let me know.
STOP! Before you do anything, familiarize yourself with the diode pack in the following picture. HEED THIS WARNING: if you bend the leads on this device at all, they will probably break off right where they exit the case. These particular components are no longer manufactured! YOU HAVE BEEN WARNED!
One more thing: there are voltages inside this unit that can easily kill you so PAY ATTENTION TO WHAT YOU ARE DOING! Do you have a dish ready to hold all of the screws so you don’t lose any?
Power Supply Caps: Get the top and bottom covers off. Before you touch anything, measure the voltage across the big caps to verify that they are discharged (you should do this after every every time you apply power throughout the process). It’s easier to undo the big power supply cap clamps such that you remove two at a time. Make sure to take a picture or write down the orientation of the caps with regard to polarity before you remove the originals. You may need to open up the wire terminals to accept larger screws, depends on the brand of caps you buy. If you do need to open them up, whether you use a drill or a rat-tail file, use a towel or something to keep the filings from falling inside where you might not find them until they make their presence known by shorting something. Once you get the new ones in, check them 10 times against your diagram or photo just to make sure you put them in the right way. Plug your SPEC 4 into a dim bulb tester with a 100 watt bulb in it and power it up to make sure everything is normal. (The first time you do this it will FREAK you out because it needs to draw so much power that the soft start relays won’t completely engage and you will hear a loud buzzing from them for a few seconds until the caps charge. Remain calm for a few seconds.) If everything seems normal, power it off, unplug it and proceed to the next part. If things aren’t right, recheck your work and/or get help.
Meter Board: Disassemble the front panel until you can get at the meter board. Cover your big beautiful meters with a towel so they don’t get scratched! Proceed to recap. On my SPEC 4, C1 and C11 were different as indicated in my parts list. C16 was in the parts list and in the schematic but not shown on the parts layout diagram. My rule is: if it was working satisfactorily before you started, put the same value of parts back in that you remove as opposed to changing them to what you see on the parts list or schematic. The only exception to this is if someone has been in there before you and there is an obvious hack-job. Please also note that on the parts layout I have, C13 is shown in the INCORRECT orientation. Verify with the schematic!
Once I finished the recap of the meter board, I very carefully checked operation on the dim bulb tester again before I went to the next stage. I think it’s good practice to test after making a change because it makes it easier to troubleshoot if you do make a mistake. If everything is ok, it’s probably a great time to Faderlube the front panel volume pots and Deoxit the power switch. Reassemble the front except for the aluminum panel and rack handles.
Amplifier Boards: Take a picture or make a drawing of what connectors go where and what color wires go where so you can put them all back in the right place later. Do one amp board at a time. Disconnect the 4 wires and 2 connectors. Carefully remove the amp module from the chassis. Mark the output transistors so you will know where to put them back. Unscrew each output transistor and pull them out of the sockets, and off of the heat sink. CAREFULLY remove the mica washer under each output transistor. Remove the screws holding the board onto the heat sink brackets. CAREFULLY remove the single screw holding the diode pack in place (DON’T BEND THE LEADS). CAREFULLY remove the power amp board from the heat sink and set it aside. Remove the 2 steel heat sink mounting brackets. Clean all of the old heat sink grease off of the transistors, mica washers (careful, they are brittle) and heat sink. You may also want to wash the heat sink at this point. Proceed to recap the power amp board. Be careful not to change the settings of any of the variable resistors. Replace VR1 and VR2. Reassemble the power amp board back onto the heat sink (once again being very careful of the diode pack). Apply fresh heat sink grease to the bottom of the output transistors. Apply the mica washers onto the bottom of the output transistors then apply heat sink grease to the clean side of the mica washers. Place the output transistors back in the sockets and screw them in place. Do it all over again with the second amplifier board. Carefully reassemble the amplifier modules back into the chassis and reconnect everything as per the drawing or photos you made earlier.
Testing and Adjustment: Go find a long skinny flat blade screwdriver that you can use to adjust VR1 and VR2. Cover the metal shaft with heat shrink tubing so you don’t accidentally short something in the process. Connect the SPEC 4 to your dim bulb tester (nothing else connected) and turn it on. The bulb should be bright and then dim, and in 10 or 20 seconds, you should hear the protection relay click. If not, troubleshoot and/or get help. If all is well, adjust VR1 to obtain zero volts between + and – of the speaker terminals. Adjust VR2 to get as low a reading as possible (close to zero volts) between terminal 26 and terminal 16 (see the service manual for location and USE CLIP LEADS ON YOUR VOLT METER SO YOU DON’T SHORT SOMETHING ACCADENTALLY). Adjust VR1 and VR2 on the other power amp board. If you can’t get both settings close to zero volts, you have a problem (troubleshoot and/or get help). If all is well, power off. Plug into mains, power on and perform the adjustments for DC Balance and Idle Current as shown in the service manual.
Reassemble and enjoy!
Hey wait, you didn’t adjust the Power Limiter or Meter Amplifier. You’re right. I didn’t move the pots while recapping and didn’t change any parts that would require them to be adjusted. Plus, I don’t have a 4 ohm dummy load so, I left well enough alone.
As I write this, my SPEC 4 has been running for about 4 hours with no issues and it sounds awesome!
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