RT-707 noise

[BobbyN]

Hi all, My RT-707 has the dreaded noise on only the right channel in source mode only but that noise does get recorded so it can be heard on quiet passages. I've read that it's most likely caused by one or more of the six 2SC1344's on the record/mic amp board. I've read that a good replacement is KSC1845. Do I have that number correct?

My other question is can this board be accessed by just removing the top? Replacing six transistors is no problem but just curious how much time It'll take getting access to that board.

I also need to replace the power switch button, not the switch itself, just the button. The plastic piece is broken and has been temporarily fixed so I need a new one. Any ideas where to get this part?

I have done the counter belt so I'm wondering if I broke that switch part when I removed the face plate???

Any other recommendations are very welcome.

Thanx, Bob

 

[QSilver]

1845 is the right transistor I think but if the hiss is being recorded, there are two of these noisy transistors on the record PCB too. The board is accessible from the bottom but you'll have to remove the face plate to access the screws holding it in place. You might need to cut a couple cable ties too to get enough cable length to pull the board out from the bottom.

 

[BobbyN]

1845 is the right transistor I think but if the hiss is being recorded, there are two of these noisy transistors on the record PCB too. The board is accessible from the bottom but you'll have to remove the face plate to access the screws holding it in place. You might need to cut a couple cable ties too to get enough cable length to pull the board out from the bottom.

QSilver, You say the record PCB, you mean the "power and oscillation board" RWR-053?
I did notice there's two of the 2SC1344's there for each channel coming from the mic amp RWF-065. Makes sense.
Thank you.
Bob

 

[QSilver]

QSilver, You say the record PCB, you mean the "power and oscillation board" RWR-053?
I did notice there's two of the 2SC1344's there for each channel coming from the mic amp RWF-065. Makes sense.
Thank you.
Bob

Yep, thats what I meant, sorry. Glad it helps. One thing to check is if the hiss is audible on the "source" position of the"source/tape" switch. If it isn't, its likely those two transistors on the power/oscillation board. If it is audible, then its on the Mic pre-amp board. Don't be sidetracked my the mic-pre amp board's name. It is also the LINE IN pre-amp. Just in case you were wondering.

 

[BobbyN]

Yep, thats what I meant, sorry. Glad it helps. One thing to check is if the hiss is audible on the "source" position of the"source/tape" switch. If it isn't, its likely those two transistors on the power/oscillation board. If it is audible, then its on the Mic pre-amp board. Don't be sidetracked my the mic-pre amp board's name. It is also the LINE IN pre-amp. Just in case you were wondering.

QSilver, Yes the noise/hiss (sounds like somebody left the hose running outside) is ONLY in the source position. It is NOT in the tape position but it will be recorded. Obviously after the tape has been recorded you do hear the noise when played back. Previously recorded tapes are quiet when played. This is only in the right channel but from what I've read I'll eventually get it in the left.

After this is done there's another thing I have to address. When going from either stop or pause, there's a "jerk" in the tape as it starts. It's kinda like the take up reel starts before the pinch roller makes contact with the capstan. At that moment I can see the tape leave the heads. This is very quick, only a fraction of a second. I do not have any type of gauges to do any mechanical adjustments, I can only do electronic but maybe someone has an idea that I can try while I'm in there. Of course without any gauges it would have to be a trial and error thing that would be able to go back easily if it didn't work. Hope that made sense. My gut feeling is to leave that alone and live with it.

Thanks again, Bob

 

[QSilver]

Your problem is likely in the mic pre-amp board then. when replacing the transistors be careful with the orientation as they CAN be different. I believe the old ones are EBC and the 1845's are usually ECB. If you follow the silkscreen on the board you should be fine.

For the tape jerking, you really need to check the tape tension with a gauge. The adjustment can be quite subtle - hard to judge without a gauge and the tensions are adjusted with the large wire wound resistors or rheostats on the top of the unit. I would suggest you try and pickup a tension gauge - 500g or something similar to do the torque and tension setup. You'll probably get lucky and only pay a relatively small amount. Well worth it in the long run.

 

[BobbyN]

Your problem is likely in the mic pre-amp board then. when replacing the transistors be careful with the orientation as they CAN be different. I believe the old ones are EBC and the 1845's are usually ECB. If you follow the silkscreen on the board you should be fine.

For the tape jerking, you really need to check the tape tension with a gauge. The adjustment can be quite subtle - hard to judge without a gauge and the tensions are adjusted with the large wire wound resistors or rheostats on the top of the unit. I would suggest you try and pickup a tension gauge - 500g or something similar to do the torque and tension setup. You'll probably get lucky and only pay a relatively small amount. Well worth it in the long run.

Yes I think you're right about finding a gauge. Can't ever have too many tools! If you happen to see a link to a gauge I would like to see what you recommend.
I'm familiar with the pin-outs between the different transistors. I've used these 1845's several times rebuilding my receiver.
This is my second 707 that I just got from a friend/neighbor so I know it's history. It hasn't had too many hours on it and the heads don't appear to have as deep of grooves as my original. It just needed a counter belt which I took care of. It has a great sound except for this noise I've mentioned. My original is quiet as can be on source, or anywhere. I don't know if anything was don't to it B4 I got it. I've had it since the early 2000's and I haven't been into it at all.

Thanks again. Bob

 

[QSilver]

I think its just down to chance with those transistors... I have two and the first one was silent for a long time and then I recently went through it. Sounds amazing now - even the VU's are faster to respond. My second one though, now looks like a shadow in comparison and it is starting to get noisy in the input like yours.

I had a quick look and I saw this as a tension gauge. It's similar to mine except mine only goes up to 500 Gramm. But something like that I think would be the best thing to go for.
http://www.ebay.com/itm/Scherr-Tumi...602952?hash=item28188d43c8:g:o44AAOSw8sBW6xxI

Hope that helps!

 

[BobbyN]

Will keep you updated. Maybe get to the transistors this weekend.

 

[BobbyN]

I worked on it over the weekend and it's all fixed! The problem child was Q206, for the R channel and one other that was putting a little noise in the L channel. I replaced all six on the mic amp board anyway. Now it's nice and quiet. New counter belt and a brake adjust took care of the pause jerking issue, head de-mag and cleaning and all is well.

QSilver, thank you very much for your ideas etc. It saved me a lot of diagnostic time!

Bob

 

[QSilver]

Glad you got it all sorted! No problem, glad I could help and great that you got all those other problems solved too.

 

[BobbyN]

Glad I had those 1845's on hand. When I worked on a receiver I had to order some of those so I ordered several extras for a rainy day so it was nice to have them on hand. After shipping the cost is minimal.
Thanks again.
BTW, my "other" 707 has one main issue that I'll start a thread on later.

Thanks again, Bob

 

[soundmig]

A couple of questions for you guys with RT-707 experience. Are the 1845's that Mouser sells the correct transistors? If so, is there anything about the pin configuration that is different or do they just "drop-in"? Also, does the faceplate have to come off for belt replacement (or any other work)? If so, how does one get the pitch control knob off of the pitch control? I see the others just pull-off, does this one pull-off also? I pulled pretty hard and it didn't come off and I don't want to break anything. Let me know

 

[BobbyN]

A couple of questions for you guys with RT-707 experience. Are the 1845's that Mouser sells the correct transistors? If so, is there anything about the pin configuration that is different or do they just "drop-in"? Also, does the faceplate have to come off for belt replacement (or any other work)? If so, how does one get the pitch control knob off of the pitch control? I see the others just pull-off, does this one pull-off also? I pulled pretty hard and it didn't come off and I don't want to break anything. Let me know

I had to use pliers to pull the pitch control knob off so I can relate to the problem you're having.
Yes the front panel needs to be removed to get to the belt. After that it's just patience.
I don't remember about the pin outs on 1344's but the 1845's are ECB. Keep a data sheet in from of you and you'll be fine.
Bob

 

[BobbyN]

Soundmig, I should have mentioned, the PC boards are labeled so if you have the data sheet for the 1845 in front of you it'll be easy.
Bob

 

[QSilver]

Just a tip for the pitch knob, I usually use some thick soft cotton strap (can't remember its proper name at the moment) for any tough to remove knobs. I take a loop in my hand and put the center of the loop behind the knob as best i can and then pull. Usually it works quite well with the added bonus that because its soft and cotton, it's less likely to damage the knob itself or surrounding decoration.

 

[soundmig]

Thanks for the tips WE6C and Silver! I appreciate it.

 

[Valvista]

Just a tip for the pitch knob, I usually use some thick soft cotton strap (can't remember its proper name at the moment) for any tough to remove knobs. I take a loop in my hand and put the center of the loop behind the knob as best i can and then pull. Usually it works quite well with the added bonus that because its soft and cotton, it's less likely to damage the knob itself or surrounding decoration.

For the second time a knob at the bottom of my RT-707 popped out (fractured actually). I put a new one on and it snapped in but it's not completely seated and protrudes more than it should. Thinking there may be a fragment of the old knob lodged in there. Was reluctant to apply much force to the knob to remove it again for fear of breaking either the knob or the switch shaft that engages it. Your suggestion sounds good & will try it. I infer from it, also, that the knob is removable by simply pulling hard enough to move past the detent. Thanks for the post. It helps to keep this RT-707 in the analog mix at my home.

 

[BobbyN]

My pitch control knob didn't go back completely however you wouldn't know unless you really looked closely at it so I just left it that way.
Glad your 707 is going strong!
Bob