964Cup

I've just gone through the process of replacing the BC337. It all seemed to go fine, I've checked that the solder connections are good (for amateur work) and there are no shorts. I've checked the harness and have power to all the right pins (K2 permanent, G35 & 29 switched; I've also checked all the fuses including fuse 11 in the engine bay). When it's all reinstalled the front panel lights come on correctly with the rest of the cabin illumination. But...that's it. No CCU fan, no cabin fans, no flaps, no AC. I really can't see how what I've done could have fried it completely, but I seem to have managed somehow. Or am I missing something? I've taken it out again and have it apart in case there are any tests I can do. I have a multimeter, but no Hammer/OBD reader, and I'm in rural France so I'm a bit short on local expertise... Help!

user 783003

My CCU was having very similar symptoms. The fix was re-soldering one pin on the CCU.

See pics. If you’re not looking for it, you’ll miss it. Notice inside the red circle below, the whole square inner solder joint has failed. I just added solder to this and that fixed my issues.

DLR

Hi,

i have a question concerning the 993 ccu not shutting down after 20 min.

I've tested all BC337 (soldered them out) and they all seem to be fine.

I can't see any solder cracks on both pcb's. Checked a lot of components and everything seems to be fine so far. Vent motor is OK. Got some new lithium grease.

The only real problem i was able to locate was a sensor really full of dust. Can this also cause the ccu not to shut down or must there be an electrical problem somewhere else.

Thanks in advance.

ToreB

Fluff on the interior temp sensor will only make it difficult for the unit to measure the cabin temperature.
Please be aware that the unit is supposed to be on for up to 20 minutes after ignition off. This is done to ensure correct temp regulation after short stops such as filling gas etc.
Transistor T1 is the culprit when the unit does not shut down within 20 minutes. We always change this transistor in our standard CCU repair procedure.
Cheers,
Tore

DLR

OK.

Well i think T1 is OK, but i can only test it with a simple tester at the moment. Don't have a transistor curve tracer at the moment to test them in detail.

Will replace it as a precaution.

Thanks for the advice.



Also cleaned the ntc very cautious.

systemsc

The shutoff problem is a function of the Beta of T1. The 964/993 CCU analog circuit design for the system shutdown is marginal.

DLR

Thanks for your input. As i still have no access to a transistor curve tracer and only have a cheap chinese transistor tester that only shows hFE and Uf, i have a question.

The original BC337 measures at hfE 501 and Uf 648 mW.

The new transistors measure at hfE 442 and Uf 607 mW – and other values.

From my understanding a lower Uf might be better. There are some that measure at 368 mW. What do you think / recommend? At the moment i don't understand the circuit in detail, so i'm not able to calculate the ideal transistor values.

Thanks in advance.

ToreB

The current gain value is irrelevant in this application, this transistor switches the relay on and off. As mentioned, if you have power off problems, change the transistor.
Cheers,
Tore

systemsc

You can immediately determine whether T1 is bad by using an ohmmeter and checking the collector to base & the collector to emitter for low resistance, with T1 removed.
If T1 is OK (often), then the #15 input to the CCU at key-off may not fully reach 0V at the base of T1, causing T1 to remain conducting and not powering down the CCU.
It's not always as simple as just replacing T1. I've tested many 964/993 CCUs over the last 20+ years where replacing T1 isn't always a fix, especially when the audio
system has been modified, e.g. a booster amp with large input capacitors affecting the #15 input voltage.