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Help Wanted: RT-909

wanders

wanders

Super Member
I acquired a non-working rt-909 a couple of weeks ago. Been following Pultelniark’s thread on restoring a rt-909. While experimenting with operations, the machine made a loud snap, like a home circuit breaker, and stopped working. Here’s what I’ve found, from the beginning.

- On first inspection, there were a lot of broken-off, missing, or burred-out connectors. The covers had been ham-handedly removed. Inside the unit is pretty clean; looks like it has had limited use and wear.

- Pinch rollers were used, but firm, not tacky; believe that they are original.

- The capstan belt was stretched and draped over the capstan flywheels; it was a little tacky, but not gooey. When I removed it, it was about an inch longer than a new belt. Of the four screws holding the capstan motor brace, the two right side screws were in place, but damaged, appears they had been removed at one time. The two on the left side (harder to get to) were damaged and very tight. Believe those may never have been removed. All of this leaves me to believe that the belt had become too loose to work, somebody had tried to replace it, but gave up when he couldn’t get the capstan brace off. I serviced the capstan flywheels and replaced the belt. Both bearings were in place. Using a 9v battery, verified that the capstan motor worked quietly.

- A couple of the screws holding the tension arms in place were missing or damaged. Don’t know for sure if anyone had succeeded in getting the assemblies off, but they seemed to work properly and all the parts were there. The lube was pretty dry, the contact cement holding the springs in space was dried out and crusty. Rebuilt the assemblies as instructed; replaced both micro-switches with the latest model, Omron ss-5gl13f, from Digi-Key.

- The forward play, reverse play, fast reverse, and pause switches all (with the micro switches engaged) caused the servos to activate; but not correctly. The pinch roller assembly would raise, but not stay engaged. Fast forward, or fast reverse caused the reels to move fast, but the indicator always indicated reverse. During some operations, the capstan motor ran. While waiting for the micro switches to arrive, I was experimenting with the various functions to see if I could spot a pattern when the deck stopped working.

- As discussed, there was a loud snap akin to a home circuit breaker tripping; there was no smell or other evidence of burning. Following that, the lights come on when the power switch is activated, but none of the control switches activates any servos. After the snap, I checked the fuses (which I had not done before that time). There are a 2a and a 4a nose to tail. A 2a fuse was in the 4a bracket, and a 4a fuse was in the 2a bracket. The 2a fuse was burned out. (again, don’t know if that was the case before the incident). All the other fuses appear ok. I have a rt-707 in the garage which was badly damaged in shipment; been using that to replace the damaged fasteners on the rt-909. Replaced both the 2a and 4a fuses with comparable 707 fuses, but no change. Picked up new radio shack fuses (only 250v available), but no change.

My sense is that this is a nice machine with very little use and it’s worth taking some time and effort. At this stage it seems important to attempt to diagnose whatever the underlying problems are. Pultelniark’s comments deal with restoration of a machine that is working. I’m competent mechanically, but I don’t know much about electronics or electronic theory. Maybe I’m going to have to get a text book; but, any advice would be appreciated.
 
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wanders said:
- The forward play, reverse play, fast reverse, and pause switches all (with the micro switches engaged) caused the servos to activate; but not correctly. The pinch roller assembly would raise, but not stay engaged. Fast forward, or fast reverse caused the reels to move fast, but the indicator always indicated reverse. During some operations, the capstan motor ran. While waiting for the micro switches to arrive, I was experimenting with the various functions to see if I could spot a pattern when the deck stopped working.
Click to expand...

My 909 that I finished re-building had this issue also. I had a bad logic control IC on mine (as well as a few other toasted items). The logic IC is on the small board that has the function buttons on it (FF, REW, etc.) I wound-up replacing the board as a new IC was difficult to find. You can troubleshoot the IC by shorting certain pins to ground to test the functionality. This is not for the novice troubleshooter though, but if you feel comfortable doing this then go for it.

I just found it, it's IC501 (AN6251) on the "Control A" board. This chip controls all the timing and logic for operation. If you Google the AN6251, you can find a datasheet that will give you the pin-out for the functions.

Try looking for my thread when I was doing my 909, I asked a lot of questions. There are a lot of very helpful and knowledgeable people here, you'll fix it.

Good luck!
Glenn

EDIT:
You may get more help in the "Tape" forum. Lot's of 909 owners there.
 
The counter going backwards is normal if there is no tape loaded, no matter what direction or function it's in. It's set up this way to keep the right amount of tension on the tape at any given time. As a result, with no reels loaded the motors just spin around in opposite directions unimpeded.

When the micro switches are activated does the capstan still turn on? When you hit play do the pinch rollers still come up, even if they drop back down shortly afterwords? Will it still play in either direction, but no FF or rew, or will it still FF and rew but no play? It could be an issue with the logic board as Glenn suggests, but it may also be a problem with the motor control board. (The board that is mounted upright behind the motors.) If shorting various functions on the logic board doesn't do the trick, then test to see if voltage is still getting to the main motor board. Then go from there.
 
Numistrek09 said:
When the micro switches are activated does the capstan still turn on? When you hit play do the pinch rollers still come up, even if they drop back down shortly afterwords? Will it still play in either direction, but no FF or rew, or will it still FF and rew but no play?.
Click to expand...

Since the "snap," only the lights come on, otherwise it is totally non-responsive. Pressing any button produces no response. Tough for me to figure the next step.
 
As Numistrek09 mentioned, the motor control board is also suspect. After I fixed my logic board, I still had motor problems. I had two bad power transistors, two bad diodes, and a bad zener on mine. The power transistors that are common to fail are Q210-Q213, D221 & D222 were blown on mine, and ZD201 was also shot. These are all on the motor board that is vertically located behind the reel motors.
I had to do a lot of circuit tracing to find where I was missing voltages, but it can be done, it just takes time. You should check your motor power and work backwards to see where it's failing, common troubleshooting technique.

I forgot to mention that the service manual has a good description of how the logic works. Start on page 17 "When the power switch is turned on" and follow the explanation of how the logic works. You will probably need a scope to check if the levels are switching from low to high on the IC's. At least this way you can verify that the control is working correctly.

Good luck.
Glenn
 
The first thing to do in a case like this is test all the power supply voltages. Get the service manual and check the voltages.
 
Capacitor replacements

Found one leaking capacitor on the control b assembly; sure I'll find more. Would appreciate advice on how to identify replacements. Searching here and on the web hasn't been too productive. Tried searching Digi-Key's catalog, but there are too many variables for comfort.

Thanks
 
wanders said:
Found one leaking capacitor on the control b assembly; sure I'll find more. Would appreciate advice on how to identify replacements. Searching here and on the web hasn't been too productive. Tried searching Digi-Key's catalog, but there are too many variables for comfort.

Thanks
Click to expand...

Start with the value, say 10uF 35V. Select electrolytic capacitors. Then narrow the search by selecting 105C temp range, in stock only, radial, through hole. Panasonic FC series is a good choice. Once you get that far, just pick the cheapest one.
 
Welcome advice.

Found a second leaker. Both have temp information: one 85c, the other 90c. Should I attempt to find those specs, or is 105 good enough?

Thanks
 
105c is better than either of those lower numbers. Can't go wrong with that.

Given the issues you're finding, it sounds like you need to just recap the whole board. If several are already failing, the others may soon do so as well. Panasonic's FC and FM series will do just fine. Nichicon's PW is also a good choice. For the one big axial cap use Nichicon TVX.

Don't forget to check those transistors.

What year is your RT from? To tell, look at the two letters infront of the serial number on the lower back panel.
 
The date code is ZJ, apparently pretty late, oct '79. I think recaping the main assemblies will probably be necessary; but I'd prefer to solve the issues described earlier before rehabbing the boards.

The two bad, leaking caps are c212 on control b, which is directly in line with the blown fuses discussed. The second is c988 on the mother board; not sure how that one figures in. I'm new to this diagnosis business and I'm moving pretty slow. If there are some suspect transistors that anybody knows about, I can test those right away and order replacements with the caps.
 
Transformer

I've replaced the bad caps without any noticeable change to the operation of the deck. Also, I've spotted some suspicious transistors. However, it occurs to me that I'm probably going about this diagnosis back-a**ward. I don't find many voltage specs listed in the schematics, but, if I'm reading correctly, I did find that the ac output from the transformer to the control b board (and onward to the reel motors) were supposed to be 125 vac and 85 vac for each motor. My multimeter readings straight from the transformer were 78 & 38 for motor #1 and 52 & 23 for motor #2.

Based on these voltage readings, should I conclude that the transformer is faulty?

Appreciate any observations, opinions, etc.

Thanks.
 
Late? Late in 79 maybe, but the 909 was introduced in that year and made through 1984.

I believe the large fold out full unit schematic has the voltage numbers on it. I know one of them does, just can't remember off the top of my head.

The transformer sounds fine to me. I mean, the voltage is a little low on motor two, but not by much. I still think the problem is in the circuitry.
 
Numistrek09 said:
Late? Late in 79 maybe, but the 909 was introduced in that year and made through 1984.

I believe the large fold out full unit schematic has the voltage numbers on it. I know one of them does, just can't remember off the top of my head.

The transformer sounds fine to me. I mean, the voltage is a little low on motor two, but not by much. I still think the problem is in the circuitry.
Click to expand...

Thanks for the advice.
 
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