Pioneer RT-909 Trouble

[pustelniakr]

Now we need to add lead extenders to those Q214 leads. What I would do, if I had the unit here is take the insulation off of some 24 Ga or 22 ga stranded wire. Lay it up against the front of each lead of the part. I would then take an individual strand from the same wire, and wrap the lead extenders tightly to the leads and solder. You don't want to just solder, and you don't want to solder before you wrap. You need a good physical-electrical connection, and not depend only on solder. If you don't have a good physical connection, the extender joints will come loose when you solder the extended leads into the circuit board.

Then, I would temporarily mount the transistor to the heatsink, cut some small size heatshrink tubing and cut it to the right size to go from the bottom of the transistor to the circuit board, insulating the leads and extenders. The joints will be bigger diameter than the leads alone, and you do not want them to be able to short to anything around them. You will not need to shrink the tubing.

Take the resulting transistor/extender assembly back off. Show me a picture of the leads with extenders, without heatshrink tubing (I want to see the joints). Slip the heatshrink tubing back on the leads, and install Q214, with its insulator sheet and insulating shoulder washer, onto the heatsink, and solder it into the circuit board. Show me a picture of the finished product.

Do the work of a surgeon. Make me proud.

What a pain, but necessary.

If these instructions are not clear, let me know and I will do what I can to make them more clear.

Enjoy,
Rich P

 

[snailman]

I had 2 leads done, started wrapping the wire around the last lead lead, and it snapped!
So now I will be ordering a replacement.

On a better note, the microswitches arrived today, and I rebuilt the tension arms successfully!

 

[elnaldo]

I've used spare resistors to do those kind of extensions, the wire is very easy to work with. Perhaps this picts can help you.

 

[snailman]

That's what I was doing, except with copper wire of similar thickness. Unfortunately, the lead snapped off the transistor right at the plastic, making it useless.

It's only $0.80 to replace, but still quite annoying.

 

[pustelniakr]

That's what I was doing, except with copper wire of similar thickness. Unfortunately, the lead snapped off the transistor right at the plastic, making it useless.

It's only $0.80 to replace, but still quite annoying.

I was going to suggest that you re-replace Q214 anyway, even if it seemed to work (too much indication of potential damage from having been shorted to the heatsink). Frankly, if Q221 has also been powered when screwed to the heatsink without an insulator, it needs to be replaced also, for the same reason.

The work looks like it would have been acceptable. I take it that the pics were from a different project.

I can wait, especially since we both have to. Good show on the tension rollers.

Please verify that there is a small range of motion of each tension guide that does not involve the damping action. In other words, you move the tension arm away from its rest position, and it moves the damper which takes a bit of time to return, allowing small motions to be un-damped, but big increases in tape tension will run into the damping action. This is how you prevent the slight slack loop that would otherwise appear between the 2 capstans, and across the heads, when you initially start driving tape.

Do the tension rollers, as rebuilt, both act like this?

What damping fluid did you use?

The lube on these units tends to turn to wax over the years. Please verify that the pinch rollers can be lifted and dropped without any kind of resistance (should be completely free).

Don't forget the shrink tubing on the extended leads of Q214.

I still want to see pics of your work on Q214, once you have completed that work. The pics you showed as example are just fine, although the current capacity of the small resistor leads is questionable. I would just lay a heavier gauge along the lead, and wrap it to the lead with a 30 gauge wire, then solder the joint. If the extender is solid wire, you can tack it to the lead with solder before wrapping it and finish soldering. If the extenders are braided wire, don't solder before wrapping. I think that you will put less stress on the transistor leads if you try it that way.

Now a couple of questions. You probably stated the answers to these, but lets formally have them here, in one place...

Was there ever a time when the unit was powered up with the insulation missing from all 4 heatsink'd components (all three heatsinks)?

Was there ever a time when the unit was powered up with the insulators missing from both transistors on heatsink 1?

Good show so far,
Rich P

 

[snailman]

now a couple of questions. You probably stated the answers to these, but lets formally have them here, in one place...

Was there ever a time when the unit was powered up with the insulation missing from all 4 heatsink'd components (all three heatsinks)?

Yes, when I first replaced Q214, Q245 and ZD201. (ZD201's replacement accidentally installed as D223; original, failed open ZD201 still installed), the unit was powered for about 30 seconds, the reel motors were running forward, and the counter wasn't lit. The solder bridge between the base and collector of Q210 was present.

After realizing my mistake, I installed the correct diodes, and found and removed the solder bridge. The unit ran perfectly for about 15 minutes with the board hanging loose. At that point I turned it off, and reinstalled the board, again forgetting the insulators.

Once again, the reel motors were running forward, and the counter wasn't lit. The unit was on for about 10 seconds.

I then saw your post, and checked the fuses. FU4 and FU5 were blown.

Was there ever a time when the unit was powered up with the insulators missing from both transistors on heatsink 1?

Yes, when all the insulators were removed, but never just those 2 transistors alone, uninsulated.

I am assuming I should replace the heatsink'd transistors on control B (Q214, Q221, Q237, Q238)?

If so, are these good replacements for the other 3:

Original: New:
2SB682 MJE15033G
2SC2535 ST13005


As for the tension arms, I believe they behave as you described. I can post a video if you want.

I used 10000 cst silicone damping fluid from a local hobby shop (their brand). A guy I know is into RC cars, and had a bottle I borrowed.

As for the pinch rollers, when operated by hand, they go up smoothly and glide down slowly. When operated by servo, they move smoothly in both directions.

 

[pustelniakr]

Don't buy any transistors until I can analyze the potential consequences of the insulator error. Lets try to save some postage and time, by consolidating the order. You may not need all that you think you do, or you may need more.

I will say that many mysteries are no longer mysteries. I must warn you, that the consequences may be significantly not pretty. I'm not sure yet. I need time to digest...

The video is not necessary at this time. Just make certain that when you displace the damper, via tension guide (back and forth), it takes a bit to return to the tension arm, just not too much time. Also, when you fully rotate the tension arm, off of its rest position, then release it, is snaps back to its rest position, without damping or resistance.

Now, please return to my restoration thread and perform the portion that cleans and lubes the pinch roller mechanism, especially the pinch roller arm pivot points. The smooth action you describe indicates that you have wax instead of lube. The pinch rollers should lift and drop without any resistance (completely free, no damping, no smoothness).

I'm hoping that the solenoid operation of the pinch rollers, that you describe, was from before these electronic problems began, and that you have not applied power to the machine since you and I started. I'm sure you have not. I just need to say that, because I am a bit obsessive.

Enjoy,
Rich P

 

[snailman]

Power has not been applied since the fuses blew.

I will clean/lube the pinch roller assembly.

Is there anything else I should do at this time?

 

[pustelniakr]

OK. Here is a preliminary assessment and purchase recommendation:

While the unit was apparently running with the Control-B board hanging loose:

• The collector of Q214 (37V input to the 24V regulator) was shorted to the collector of Q221 (the output of the 5V logic supply). This was very bad mojo, and would explain the smell of hot components during this period.
• You must be prepared for this consequence: unfortunately, during this period, extensive damage could have been done to the control logic of your machine, especially to logic and unobtanium control chips. For this reason, you just might have yourself a parts unit now. Maybe not. We'll have to see.
• What would mitigate the problem above would be if the heatsink is tied to ground when the heatsink is screwed only to the circuit board (not likely since the unit tried to work that way, and I do not see ground foil at the heatsink tie points).
• Pull Q220 and test her, using meter diode test mode, posting results. If bad, let me know and we will add it to the purchase list below.
• We might have lost/damaged IC201, a small 3-terminal 5V regulator. We won't know until the initial power-on tests.

When the heatsinks were subsequently screwed to the unit, they were definitely tied to ground. This would have shorted both, the output of the 24V and 5V regulators to ground.:

• This would explain how D223 was taken out, without taking out Q214 (Q214 was bypassed by the current as it went to ground). The H-bridge was safe in this scenario.
• The counter showed no indication, at this time, because its power supply was shorted to ground.

Heatsinks 2 & 3 were connected to ground while Q237 & Q238 were not insulated from the heatsinks:

• The Q237, Q238 (L & R reel motor drive) and associated circuitry might have been spared, since the two transistors were bypassed by the shorts (their collectors were shorted to ground).
• Both reel motors would have been been driven to full speed, full torque, by the shorts. I don't see an immediate cause for concern here.

Now, for the parts to order:

• I think, as long as you are in there, you should replace the H-bridge drive transistors, Q210-213 (2SB682, replace with Mouser 512-KSA940TU, previously recommended by markthefixer). These have taken a bit of a thermal beating over the years. Two of those might still be new, from a previous replacement action. It would be good to have them all be the same part number (KSA940). If not, replace them all.
• Replace Q221 (2SB682, same as the H-bridge transistors, above), since it might have been damaged while 37V was shorted to its collector.
• Replace Q214, for the reasons you have previously stated (lead broken off).
• Order some proper heatsink grease.

I think that, once your pinch roller linkage has been cleaned and lubed, we are ready to complete the transistor replacement. Your tension rollers should be reinstalled. Ping me when this has all been completed. I will provide additional instructions. I can think of no additional "while we are waiting" work.

Enjoy,
Rich P

 

[snailman]

OK, I will test Q220.


As for the collectors of Q214 and Q221 being shorted, did you mean that they were shorted by the heatsink, while it wasn't grounded?
(The heatsinks were left attached to the unit, and unscrewed from the transistors. AFAIK there was never a time when the transistors were in contact with an ungrounded heatsink.)

When the unit ran, control B was unscrewed, and the heatsinks were not present.


When the solder bridge was present, control B was screwed in, with the transistors uninsulated. The unit smelled warm during this time, while the solder bridge was present, and the h-bridge felt warm.

After reinstalling the correct D223 and replacing ZD201, the unit ran with the board loose, as mentioned above.

When I screwed the board back in, the transistors were again uninsulated, and this time the fuses blew.

 

[pustelniakr]

OK, I will test Q220.


As for the collectors of Q214 and Q221 being shorted, did you mean that they were shorted by the heatsink, while it wasn't grounded?
(The heatsinks were left attached to the unit, and unscrewed from the transistors. AFAIK there was never a time when the transistors were in contact with an ungrounded heatsink.)

When the unit ran, control B was unscrewed, and the heatsinks were not present.


When the solder bridge was present, control B was screwed in, with the transistors uninsulated. The unit smelled warm during this time, while the solder bridge was present, and the h-bridge felt warm.

After reinstalling the correct D223 and replacing ZD201, the unit ran with the board loose, as mentioned above.

When I screwed the board back in, the transistors were again uninsulated, and this time the fuses blew.

That is news we can use. I have regained hope that we are near to being successful here. Since the heatsinks were never present while ungrounded, the only time that Q214 and Q221 were shorted together was when they were also shorted to ground. That keeps the dangerous voltage off of the control logic, and the remaining explanation of reported symptoms remains valid.

Let's order those parts, install them, complete the pinch roller linkage clean and lube, and then we can proceed to the preliminary power-on testing.

Let me know when you are ready...

Enjoy,
Rich P

 

[snailman]

OK, I am going to pull and test Q220 momentarily. Will post results.

I will then order replacements for Q214, Q210-Q213, and Q221 (and Q220 if needed).

 

[snailman]

Q220:
890mV from base (-) to collector (+)
832mV from base (-) to emitter (+)
open from collector to emitter (either polarity)
open from base (+) to collector and emitter (-)

 

[pustelniakr]

Q220:
890mV from base (-) to collector (+)
832mV from base (-) to emitter (+)
open from collector to emitter (either polarity)
open from base (+) to collector and emitter (-)

800mV for a forward biased silicon p-n junction is a bit unusual (should be around 600mV, unless it is a darlington). Q215 should be the same part. Just for sanity sake, pull Q215 (flag it as Q215, so you don't get them mixed up), and test it, posting results. If it tests the same, put them both back in, and we don't need to add it to the purchasing list. If not the same, let me know and we will find a suitable sub.

Enjoy,
Rich P

 

[snailman]

Q215:
833mV from base (-) to collector (+)
870 mV from base (-) to emitter (+)
open from collector to emitter (either polarity)
open from base (+) to collector and emitter (-)

 

[pustelniakr]

Q215:
833mV from base (-) to collector (+)
870 mV from base (-) to emitter (+)
open from collector to emitter (either polarity)
open from base (+) to collector and emitter (-)

OK. Put them both back in and make your purchase. Let me know when you are ready to proceed.

You are doing great,
Rich P

 

[snailman]

Will do.

Thank you for all your help!

 

[snailman]

OK, the pinch roller mechanism has been cleaned/lubed as per your thread. It now moves up and down with no resistance. (operated by hand)

I ordered the parts yesterday, and they should arrive by thursday or friday.

 

[pustelniakr]

OK, the pinch roller mechanism has been cleaned/lubed as per your thread. It now moves up and down with no resistance. (operated by hand)

I ordered the parts yesterday, and they should arrive by thursday or friday.

Well done. If you are a praying man, you might ask for a bit of grace, guidance, and skill. I have been doing so all along.

We are coming up to the initial power-on tests.

Enjoy,
Rich P

 

[snailman]

We'll find out soon enough.
According to tracking, the components are out for delivery today.