Damaged HVAC servos could be history
11-05-2012, 08:42 PM
#31
Rennlist Member
Figuring out these circuits and potentially improving upon them can be a fascinating project.
Can someone please spell out how, exactly these servo circuits work. Are they feedback circuits such as a variation of a wheatstone bridge? I'd love to learn more about this.
Marc G.
Can someone please spell out how, exactly these servo circuits work. Are they feedback circuits such as a variation of a wheatstone bridge? I'd love to learn more about this.
Marc G.
11-05-2012, 10:26 PM
#32
Racer
Marc,
The best I can guess based on measuring resistance across 2 of the 3 pins used that one set climbs up from infinity to zero to a few kilo-ohms while the other pin setup does the complete opposite. There must be a circuit setup that can mimic the resistance variation based on the resistance inherent in the paper circuit board and the varying length that the current must traverse to complete the circuit that becomes longer or shorter depending on the direction the whiskers are moving.
In other words the current travels down the resistance circuit climbs over the whiskers to then return via a separate pathway. each centimeter must account for X ohms in resistance. I haven't programmed PCBs before but there must be a simple schematic we can take off the current setup and then apply it to a varying resistance coating material and bob's your uncle.
The best I can guess based on measuring resistance across 2 of the 3 pins used that one set climbs up from infinity to zero to a few kilo-ohms while the other pin setup does the complete opposite. There must be a circuit setup that can mimic the resistance variation based on the resistance inherent in the paper circuit board and the varying length that the current must traverse to complete the circuit that becomes longer or shorter depending on the direction the whiskers are moving.
In other words the current travels down the resistance circuit climbs over the whiskers to then return via a separate pathway. each centimeter must account for X ohms in resistance. I haven't programmed PCBs before but there must be a simple schematic we can take off the current setup and then apply it to a varying resistance coating material and bob's your uncle.
11-06-2012, 02:39 AM
#33
Rennlist Member
Thread Starter
Hi Tore,
1. Was wondering what told the CCU to stop sending current to the pins to turn the motor? If you short the 2 pins mentioned in the first post, the motor pins will always see 37 ohms no matter where the arm is. Shouldn't this produce consistent current feed and wouldn't that rather quickly kill the motor?
2. Also, if the variable resistance units swept outside of their limits and opened the circuit, then no amount of current will ever reach the motor because its an open loop. By default, dead in the water. What may be happening with the tracks is that when a crack happens somewhere, it produces an "open loop" within an acceptable range of motion for the arm, but won't ever respond. So if we could solder over the tracks somehow, we could remedy this? This should fix the feedback loop signal created by the extra 3 pins, right?
1. Was wondering what told the CCU to stop sending current to the pins to turn the motor? If you short the 2 pins mentioned in the first post, the motor pins will always see 37 ohms no matter where the arm is. Shouldn't this produce consistent current feed and wouldn't that rather quickly kill the motor?
2. Also, if the variable resistance units swept outside of their limits and opened the circuit, then no amount of current will ever reach the motor because its an open loop. By default, dead in the water. What may be happening with the tracks is that when a crack happens somewhere, it produces an "open loop" within an acceptable range of motion for the arm, but won't ever respond. So if we could solder over the tracks somehow, we could remedy this? This should fix the feedback loop signal created by the extra 3 pins, right?
Shorting the limit switches will probably not affect this, I would guess the mechanisms normally operate well within the maximum limits.
2: Most potentiometer tracks I've seen in these servos are OK. The CCU stops the motor if the position feedback does not produce a signal that correspond with the applied motor motion signal. This is a normal fail safe function, and will cover several faults such as defective pot and motor(including limit switches), mechanical obstruction(stall) and others.
Please see my initial post, it's not the potentiometer tracs that are defective here, it's the non-resistive limit switch tracks.
It's perfectly possible to make a new PCB with more reliable printed tracks, I will try to look into this some day. However, a refurb kit would have to include a new motor as well as whiskers. (and a reliable method of fixing the new whiskers to the output gear)
Cheers,
Tore
The
12-02-2012, 02:32 PM
#34
Track Day
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Hi guys,
I'd like to introduce me into this forum:
My name is Michael, I'am the one behind partisan-autoteile.de
I found your discussion today, and so I will drop a few lines.
@ Tore
Thanks for the flowers! You are right, the solution is thorough and durable. It took me a whole lot of money and time to develop this repairing solution. But that's the only possible way, if somebody wants to take good money for this.
There is definitely no other way to fix these parts! Shorting the diodes to bypass the limiter?? Please don't do this. The motor, if it is weared, draws by far much more current than a good motor when stalled. The commutator is shorted, due to copper dust between the poles.
This will heat up the servo drivers, and they have no heat sink.
I'd like to find a partner for overseas! I know that shipping to Germany and back to the states will cost extra money and time that nobody has. If anybody is listening to this thread and is able to offer a repairing service with my kit in the states, please feel free to contact me.
I will not sell the repair in an individual way. There are some special tools required.
It is not as easy as somebody might think.
msattler@partisan-autoteile.de
Within some weeks I will be offering a test unit for the 964/993 heating system. This must be mounted instead of the CCU into the slot. Through a USB connection you can measure all sensors and control all flaps and blowers. The drawing currents of all servos and relais gets measured.
It offers a quick and reliable way to do the diagnostics of the whole system.
I'll tell you more about this when the software is debugged and good working. I need some more weeks for this.
Cheers,
Michael
I'd like to introduce me into this forum:
My name is Michael, I'am the one behind partisan-autoteile.de
I found your discussion today, and so I will drop a few lines.
@ Tore
That's a thorough and durable solution, but what a price!
There is definitely no other way to fix these parts! Shorting the diodes to bypass the limiter?? Please don't do this. The motor, if it is weared, draws by far much more current than a good motor when stalled. The commutator is shorted, due to copper dust between the poles.
This will heat up the servo drivers, and they have no heat sink.
I'd like to find a partner for overseas! I know that shipping to Germany and back to the states will cost extra money and time that nobody has. If anybody is listening to this thread and is able to offer a repairing service with my kit in the states, please feel free to contact me.
I will not sell the repair in an individual way. There are some special tools required.
It is not as easy as somebody might think.
msattler@partisan-autoteile.de
Within some weeks I will be offering a test unit for the 964/993 heating system. This must be mounted instead of the CCU into the slot. Through a USB connection you can measure all sensors and control all flaps and blowers. The drawing currents of all servos and relais gets measured.
It offers a quick and reliable way to do the diagnostics of the whole system.
I'll tell you more about this when the software is debugged and good working. I need some more weeks for this.
Cheers,
Michael
12-02-2012, 04:05 PM
#35
Rennlist Member
Partisan,
This sounds very promising. I would love to see a good, reliable fix for these servo motors. Just hope we can keep the cost under control.
My background is in mechanical engineering, with a bit a programming experience and I "play" around with soldering bit. But I don't think this qualifies me to help in the capacity you are asking. However, there are lots of smart Rennlisters out there so I hope we can get this project going.
Please keep up the strong work!
Marc G.
This sounds very promising. I would love to see a good, reliable fix for these servo motors. Just hope we can keep the cost under control.
My background is in mechanical engineering, with a bit a programming experience and I "play" around with soldering bit. But I don't think this qualifies me to help in the capacity you are asking. However, there are lots of smart Rennlisters out there so I hope we can get this project going.
Please keep up the strong work!
Marc G.
12-02-2012, 05:33 PM
#36
Three Wheelin'
Partisan
There is a market for upgraade hardware and software for the Porsche 993 heating and cooling system [all of which is now 17 years to 14 years old].
Hopefully something which will make they system much simpler than the present overly complicated and expensive [$2000 CCU, 5 x $300 servo units, plus sundry items = $4000] system.
Bring it on.
There is a market for upgraade hardware and software for the Porsche 993 heating and cooling system [all of which is now 17 years to 14 years old].
Hopefully something which will make they system much simpler than the present overly complicated and expensive [$2000 CCU, 5 x $300 servo units, plus sundry items = $4000] system.
Bring it on.
12-02-2012, 11:02 PM
#37
"Hopefully something which will make they system much simpler than the present overly complicated and expensive [$2000 CCU, 5 x $300 servo units, plus sundry items = $4000] system."
Right on with that thought!
By the way, there are a couple of outfits that rebuild CCU's, seem to be in the $350-$450 price range with good results.
Gordo
Right on with that thought!
By the way, there are a couple of outfits that rebuild CCU's, seem to be in the $350-$450 price range with good results.
Gordo
12-03-2012, 01:37 AM
#38
01-21-2013, 07:54 PM
#40
Guys, thanks for posting such detailed info, made the diagnosis straightforward - the fresh air servo is bad. I've pulled it out and opened it, like Tore says the "whiskers" look burnt on one side and the corresponding circular sweep area on the PCB looks like it has bubbled up.
High res image in case you like to gawk at burnt electronics:
https://docs.google.com/file/d/0BzxI...MzcDFyY0E/edit
Called around for a replacement, dealer costs are pretty high $500 (local) to $300 (Sunset). BTW, Sunset says my stamped part no 964 624 325 00 is unrecognized, they say the right part no is 964 624 901 00 (???) Pelican has 'em for $265
http://www.pelicanparts.com/cgi-bin/...0%281995-98%29
So I take it rebuilding/refurb is not an option?
High res image in case you like to gawk at burnt electronics:
https://docs.google.com/file/d/0BzxI...MzcDFyY0E/edit
Called around for a replacement, dealer costs are pretty high $500 (local) to $300 (Sunset). BTW, Sunset says my stamped part no 964 624 325 00 is unrecognized, they say the right part no is 964 624 901 00 (???) Pelican has 'em for $265
http://www.pelicanparts.com/cgi-bin/...0%281995-98%29
So I take it rebuilding/refurb is not an option?
01-21-2013, 08:30 PM
#41
Rennlist Member
Huh, that's funny. I just bought a new footwell electric servo unit from Sunset (993-624-325-00) for $174.29 last month. Could they vary that much from one servo to another?
The fresh air servo unit (964-624-902-00) is a very similar unit, as is the defroster servo (964-624-902-00) and the mixing temperature servos (993-572-905-00 - there are two).
The only real difference is the outside attachment levers. They all pretty much use the same PCB's and whiskers (although the 993 PCB's are built a little better). As proof of this, I took apart my fresh air servo and replaced it with the guts of my footwell servo and it worked beautifully! Still using it to this day. The cases have plastic tabs which can be open with just the pry of a screwdriver.
For what it's worth, some parts are 964 parts and some are 993's. The reason being is the 993 modified some of their servos and moved the locations of two of them. In the 964, all the servos can be found in the luggage compartment on the front cowl. Tore does a beautiful job of explaining this on his website at: http://www.bergvillfx.com/porschehvac2.html.
Marc G.
The fresh air servo unit (964-624-902-00) is a very similar unit, as is the defroster servo (964-624-902-00) and the mixing temperature servos (993-572-905-00 - there are two).
The only real difference is the outside attachment levers. They all pretty much use the same PCB's and whiskers (although the 993 PCB's are built a little better). As proof of this, I took apart my fresh air servo and replaced it with the guts of my footwell servo and it worked beautifully! Still using it to this day. The cases have plastic tabs which can be open with just the pry of a screwdriver.
For what it's worth, some parts are 964 parts and some are 993's. The reason being is the 993 modified some of their servos and moved the locations of two of them. In the 964, all the servos can be found in the luggage compartment on the front cowl. Tore does a beautiful job of explaining this on his website at: http://www.bergvillfx.com/porschehvac2.html.
Marc G.
01-30-2013, 10:38 AM
#42
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ToreB,
Will This work?
I just replaced the fresh air servo with a new one I bought on ebay 2 years ago. It started me thinking about what about next time one goes bad. We need a better and cheaper servo design. As I have done some radio controlled planes and boats, the logical solution seems to be to mount a Futaba or Hitec servo inside the standard Hella case. These come in hightorque/high voltage models, cost about $50 and are super reliable. For 1/4 scale airplanes worth thousands and very fast and dangerous, these servos give almost no failures under severe conditions. If we can get a reasonable way to wire them up so that the CCU will recognize them, this seems doable.
PS: My fresh air servo problem was a bad motor
Will This work?
I just replaced the fresh air servo with a new one I bought on ebay 2 years ago. It started me thinking about what about next time one goes bad. We need a better and cheaper servo design. As I have done some radio controlled planes and boats, the logical solution seems to be to mount a Futaba or Hitec servo inside the standard Hella case. These come in hightorque/high voltage models, cost about $50 and are super reliable. For 1/4 scale airplanes worth thousands and very fast and dangerous, these servos give almost no failures under severe conditions. If we can get a reasonable way to wire them up so that the CCU will recognize them, this seems doable.
PS: My fresh air servo problem was a bad motor
01-30-2013, 12:07 PM
#43
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Does anybody have any of these boxster servos? Could they be useful to repair 964/993 servos?
http://www.ebay.de/itm/Stellmotor-He...ht_3382wt_1141
http://www.ebay.de/itm/Stellmotor-He...ht_2539wt_1165
http://www.ebay.de/itm/Stellmotor-He...ht_3382wt_1141
http://www.ebay.de/itm/Stellmotor-He...ht_2539wt_1165
04-24-2013, 12:10 PM
#44
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I have already used partisan services for the refurbishment of two ccu servos. The price of the original parts is completely unreasonable and I thought it would be better to use partisan refurbished units.
Refurbished servos are already installed in the car and they're working properly. Service has been very professional.
No affiliations.
http://www.partisan-autoteile.de/
Refurbished servos are already installed in the car and they're working properly. Service has been very professional.
No affiliations.
http://www.partisan-autoteile.de/
04-24-2013, 01:57 PM
#45
I have already used partisan services for the refurbishment of two ccu servos. The price of the original parts is completely unreasonable and I thought it would be better to use partisan refurbished units.
Refurbished servos are already installed in the car and they're working properly. Service has been very professional.
No affiliations.
http://www.partisan-autoteile.de/
Refurbished servos are already installed in the car and they're working properly. Service has been very professional.
No affiliations.
http://www.partisan-autoteile.de/
Thank you,
