Trnsfmr_Jr
New Member
Hey there,
Justin here, Jim's son, owner operator at QRXrestore, and the one that has done most of the recapping/soldering since we started some 7 years ago. Just gonna pop in on the dolby bypass. I take the signal at the inputs to dolby circuitry, run it through the tape selector switches, then to the resistors on the dolby push button board that are the outputs of the board. R01 and R02 if I remember correctly. Tape playback is fully functional. This bypass was inspired by accidentally breaking one of those ribbon connectors that connect the two dolby boards on my own 9090. But you know, I wasn't listening to too much dolby fm anyways...
If you want to know how to adjust the diff mod I can tell you. On the F - 2624 put your MM on the 2 22ohm resistors I have put in place of the jumpers that were in R13-R16. Those are there just so that you can measure the difference between these points. I should have placed them in there so you can only get to the correct side of the resistor, while the other side of the resistors are connected together. Measure mV across these points. Adjust the multiturn trim pot I added in R11 and R12 so that your meter reads 0. This will affect offset, and the number doesn't settle till the amp has warmed up. For this reason I usually have one meter on offset, and one on those resistors. Leave the amp running for 3-5 minutes, then set both of these for 0. Once you have set one side for 0 you can move onto the other side and do the same thing. I always set bias after doing these adjustments as the offset can affect the bias to a small degree. Note: Odd numbers will be for the left channel, and even for the right.
Thanks for everyone's support
Justin @ QRXrestore
Justin here, Jim's son, owner operator at QRXrestore, and the one that has done most of the recapping/soldering since we started some 7 years ago. Just gonna pop in on the dolby bypass. I take the signal at the inputs to dolby circuitry, run it through the tape selector switches, then to the resistors on the dolby push button board that are the outputs of the board. R01 and R02 if I remember correctly. Tape playback is fully functional. This bypass was inspired by accidentally breaking one of those ribbon connectors that connect the two dolby boards on my own 9090. But you know, I wasn't listening to too much dolby fm anyways...
If you want to know how to adjust the diff mod I can tell you. On the F - 2624 put your MM on the 2 22ohm resistors I have put in place of the jumpers that were in R13-R16. Those are there just so that you can measure the difference between these points. I should have placed them in there so you can only get to the correct side of the resistor, while the other side of the resistors are connected together. Measure mV across these points. Adjust the multiturn trim pot I added in R11 and R12 so that your meter reads 0. This will affect offset, and the number doesn't settle till the amp has warmed up. For this reason I usually have one meter on offset, and one on those resistors. Leave the amp running for 3-5 minutes, then set both of these for 0. Once you have set one side for 0 you can move onto the other side and do the same thing. I always set bias after doing these adjustments as the offset can affect the bias to a small degree. Note: Odd numbers will be for the left channel, and even for the right.
Thanks for everyone's support
Justin @ QRXrestore