Restoring a Pioneer RT-909 Reel-to-Reel

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The purpose of the heat sink is heat dissipation. The compound enhances the heat dissipation between the heat sink built into the transistor and the heat sink attached to the frame. At the same time the transistor requires electrical isolation from ground. When a ground connection is required for the transistor it will be provided by a circuit board trace.
Just for grins, with no power check the resistance between the transistor and its heat sink.
BTW, remember that the polarity orientation of the bridge components is important.
 
Since I need things to be simplified for me, I have uploaded the picture of the components we are discussing, I just want to confirm I have this correct.

The first picture shows the screw, then the plastic washer, then the transistor shield correct? When I heard the term washer, I was thinking of a typical flat round washer, but I don't have anything like that.

The second and third pictures are a mock assembly of the components on the transistor, where the shield is against the metal in the chassis. The metal part of the transistor that is attached to the washer through the screw is the transistors built in heatsink correct? And that part should not have any contact with the screw or chassis ( infinite resistance)

Thanks guys, I realize this may be very basic stuff for some of you, but I don't have much experience with components at this level and I want to make absolutely sure I do everything in the proper manner.
 

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Yes, you are correct. However, this is not part of the bridge circuit. If you replace this make sure the new part is equivalent to the one being removed.
 
Yes, you are correct. However, this is not part of the bridge circuit. If you replace this make sure the new part is equivalent to the one being removed.

Agreed, I've replaced the four transistors and two diodes of the bridge circuit and that is it. For the heatsink components I will just have to clean off the thermal paste and reapply and reattach everything. Paste should be on both sides of the plastic sheet correct? What is the best way to get rid of the old paste? any suggestions on applying the paste, I think its going to be a bit tricky as I'll have to attached the sheets first tot the chassis and then possibly put the paste on the sheet. would a bead the size of a grain of rice do ?
 
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Agreed, I've replaced the four transistors and two diodes of the bridge circuit and that is it. For the heatsink components I will just have to clean off the thermal paste and reapply and reattach everything. Paste should be on both sides of the plastic sheet correct? What is the best way to get rid of the old paste? any suggestions on applying the paste, I think its going to be a bit tricky as I'll have to attached the sheets first tot the chassis and then possibly put the paste on the sheet. would a bead the size of a grain of rice do ?
Be sure to use non-conductive thermal grease. DO NOT use the thermal grease designed for computer CPUs. The computer grease is conductive. You will let the magic smoke out of your deck.

Enjoy,
Rich P
 
Be sure to use non-conductive thermal grease. DO NOT use the thermal grease designed for computer CPUs. The computer grease is conductive. You will let the magic smoke out of your deck.

Enjoy,
Rich P

thanks, i have dow corning 340 as per your recommendation in another post.
 
any tips on how to remove the old paste? also how much should be reapplied? sparingly or a thick layer?
Thin.

Be careful about just replacing parts unitl a unit works. You need to verify that parts are bad, or good, so you can trace the cause for the demise of the bad ones. Otherwise, you can blow up good ones as quick as you can reapply power.

The drive motors need to be free and smooth turning. I mention a bit of tri-Flo lube. Just a small amount on each end, of each motor.

The work you are doing requires electronic troubleshooting expertise. I used to guide such work, but do not have time these days. If your problem is not solved by the actions you are doing, just be aware that more damage can easily be done.

Be careful.

Rich P
 
This is what sweet success sounds like!
click picture below!



Thank you ALL for your help. I could not have done it without the million questions and answers I got here. I hope this thing doesn't give me anymore trouble anytime soon.
 
Kevin,

You are welcome, just giving back. This thread has been a big benefit for learning, from Rich P, Mark the Fixer, R-2-R, Matrix, and others help to understand the howtos of troubleshooting these decks. A big thanks goes to all the participants and members here and other threads at Audiokrama!

Regards, Walter.
 
she hums and hums along beautifully. ONe thing I did notice is she gets pretty hot. Has anyone done anything interesting to keep these beasts cool during operation?

This looked really interesting to me
8734c11abig.jpg
 
Hi, first off may I say thanks to all the efforts in this thread to restore and assist with fellow enthusiasts, it is simply invaluable.

My rt-909 has developed a fault in that it auto plays upon powering on. All functions appear to work ok apart from this, ie: FF/RW, stop (then auto plays again) etc.

I'm assuming the microswitches on each tension roller?

Any help appreciated.
 
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:(
Hope someone can chime in and help me out. I really don't feel I can get right down to the microswitches in the tension rollers if it is likely not to be those without fear of affecting some functionality.
 
:(
Hope someone can chime in and help me out. I really don't feel I can get right down to the microswitches in the tension rollers if it is likely not to be those without fear of affecting some functionality.
This may not be a DIY job, if you are not a tech.

If you have not been working on the deck and it just began to act this way, you may have a dirty "TIMER START" switch. Work that switch 100 times, slowly. If that helps, DeOxit D5 will be your friend.

If you have been working on the deck, you may have a pinched wire, or some other issue, related to your work.

You may have an electronic control logic problem that is definitely not a DIY project, and may require a parts unit for needed control logic chip(s) (if any). Transistors and other semiconductors can be substituted, but logic chips will likely be no longer available. I have not been into one of these recently enough to guess.

Normally, if the TIMER START button is ON (LED should light), the unit will automatically play or record on power up, depending upon the positions of the REC MODE switches. If they are ON, the unit will record. If they are OFF, the unit will wake up and play.

Good luck,
Rich P
 
Thanks for the reply.
I've used some contact cleaner on the timer switch and given it the usual rigorous workout but sadly to no avail.
When holding the left tension roller up and powering on, the system does not auto play but it does when holding the right one up. If I press and hold stop for a few seconds, the autoplaying stops but then neither play function works at all after that!
 
First of all, thanks to pustelniakr foor this amazing thread! Kudos for the detailed write-up.

Currently rebuilding my newly acquired 909. So far I've replaced the capstan motor belt, re-built the motor itself, and have also replaced the pinch roller rubber.

Currently in the process of re-building the tensioners and am having some issues dismantling the assembly.

I've removed the initial section and am currently at the tap plate. Cant seem to figure out how to get the little metal rod (tap plate) out to be able to access the rest of the tensioner. I've managed to lift the rod out of the crevice , but the outer raised edge of the guide case prevents it from being lifted up further to be removed. (see pic).

Would appreciate some advice on how to dismantle the rest of the tensioner from someone who has done this in the past.

Thanks!
 

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I have read this thread several times and learn something new every time. Really excellent thanks for your efforts Rich.
 
Hello…I'm reviving this fantastic thread. I came to own an RT-909 in the last week and it had/has a rewind problem. I have the service/users manual(s) made myself familiar with them and read this thread a couple of times. Per the service manual Take Up Torque and Back Tension Torque Adjustments the post on the Control B assembly are used in conduction with a spring scale to adjust for 10.5 inch reels and 7 inch reels. I followed the directions to the letter. The deck worked flawlessly. I went back to the deck the next day to use it and it's like I adjusted nothing. I played with VR204 and VR203 and got all functions back. The left motor seems to be getting too warm. I'm going back and recheck the tensions with my spring scales. Now the question(s) in the last few posts to this thread an issue about 4 transistors and 2 diodes on the B board H bridge? I can't figure out what this was done for. Was it to stabilize the functions of the control board? I also read about a problem Pioneer had with a regulator in the 24V supply section. Could this have any impact on my problem? Any help would greatly be appreciated.
 
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