Hi All. My first post here, and I wanted to highlight my experience so far with the 2226B amp. I went shopping at a local store in Vancouver BC and on the bottom shelf was a 2226B in what looked like in pretty good shape. It was however as-is because it had scratchy noise on one channel and the store owner advised it needed a new volume control. So $200 later and on the bench, sure enough when adjusting the volume control consistent noise occurred. I also noticed there was a different kind of noise on both channels when sitting idle.
I discovered after examination that this amp had been worked on by someone else. The preamp board had a few transistors soldered to the solder side of the board, a bunch of re-soldering was done, and that LED lamps were installed. Not to mention the usual amount of grime inside everywhere. I am guessing the previous restorer gave up and traded it in or sold it.
So Thankfully I found the service manual located at 'HiFi Engine' web site.
With my scope I found the signal at the Preamp out JE 23 & JE 24 were jumping around and unstable. This connects to the pre/out jacks and to J706/J707 on the power amp bd. Signals before that last transistor stage were fine. Examining the circuit with Q 714 & 740 puzzled me at first until I saw the connection to J705. It shorts to ground thru the power switch (the other pole of the power switch). I unplugged and put an ohmmeter on J705 to Gnd and yes the resistance was bouncing around a lot. Disassembly of the power switch was then done (quite easy by prying out 2 tabs) and cleaning both contacts with a contact cleaning burnishing file (mine came from PK Neuses long ago). Totally fixed the problem and the audio was much more stable until the volume control was turned.
Next rabbit hole was why the noise on the volume control? Turns out there was 10 VDC on the high side of the vol. pot and very intermittent. I removed the first transistor QE02 after the pot as a just in case thought, but that did nothing except kill the audio on that channel. Besides the 10 V was on the high side of the pot and not the arm. I could not understand where the voltage was coming from so I started to Dri-wick up a lot of the solder and discovered the problem located at the mono pushbutton. I applied minimal amounts of solder to each switch position as the traces are quite close together. Problem totally gone, so the lesson is if re-soldering the switches keep the solder to a minimum. It was surprising that this shorted condition was very intermittent (in the way of a short) and yet consistently there, while not being visible at all. Electrically JE07 & 08 supply DC power to the tuner to enable mono, while the other pole of the switch joined the two high side volume controls together.
Finally I discovered a similar full time short when in FM tuner mode. Only one channel was working and after dragging my X-actor knife around JE19 and associated pushbutton traces, problem disappeared.
So I hope my lessons learned from this will help others do a successful repair.
Doug
I discovered after examination that this amp had been worked on by someone else. The preamp board had a few transistors soldered to the solder side of the board, a bunch of re-soldering was done, and that LED lamps were installed. Not to mention the usual amount of grime inside everywhere. I am guessing the previous restorer gave up and traded it in or sold it.
So Thankfully I found the service manual located at 'HiFi Engine' web site.
With my scope I found the signal at the Preamp out JE 23 & JE 24 were jumping around and unstable. This connects to the pre/out jacks and to J706/J707 on the power amp bd. Signals before that last transistor stage were fine. Examining the circuit with Q 714 & 740 puzzled me at first until I saw the connection to J705. It shorts to ground thru the power switch (the other pole of the power switch). I unplugged and put an ohmmeter on J705 to Gnd and yes the resistance was bouncing around a lot. Disassembly of the power switch was then done (quite easy by prying out 2 tabs) and cleaning both contacts with a contact cleaning burnishing file (mine came from PK Neuses long ago). Totally fixed the problem and the audio was much more stable until the volume control was turned.
Next rabbit hole was why the noise on the volume control? Turns out there was 10 VDC on the high side of the vol. pot and very intermittent. I removed the first transistor QE02 after the pot as a just in case thought, but that did nothing except kill the audio on that channel. Besides the 10 V was on the high side of the pot and not the arm. I could not understand where the voltage was coming from so I started to Dri-wick up a lot of the solder and discovered the problem located at the mono pushbutton. I applied minimal amounts of solder to each switch position as the traces are quite close together. Problem totally gone, so the lesson is if re-soldering the switches keep the solder to a minimum. It was surprising that this shorted condition was very intermittent (in the way of a short) and yet consistently there, while not being visible at all. Electrically JE07 & 08 supply DC power to the tuner to enable mono, while the other pole of the switch joined the two high side volume controls together.
Finally I discovered a similar full time short when in FM tuner mode. Only one channel was working and after dragging my X-actor knife around JE19 and associated pushbutton traces, problem disappeared.
So I hope my lessons learned from this will help others do a successful repair.
Doug
