A/C board fix question

[fishtail]

The A/C board failed recently on my '93. I researched the probable cause on here and followed the advice to get all the capacitors replaced. They were replaced by a friend who has a lot of electronics experience (30 years in widgets for aircraft). He used uprated (tantalum ?spelling?) caps.
It worked fine for a couple of days and then one of the new caps (replacement for C6) went up in smoke. I've had the cooked cap replaced, but it appears that the nearby component labelled Q3 has also been heat damaged. It looks like a power transistor with an integral heat-sink. Does anyone know what it is, and the part number for a suitable replacement? Thanks.

 

[Briank]

I believe it is a Toshiba motor driver IC. I will look up the info and get back to you later.

 

[fishtail]

Thanks for the fast reply. Any info you can provide would be greatly appreciated. I would have sent it to you for repair in the first place, given all the good reviews on here, but I'm in the UK and was trying to get a quick fix...

 

[Briank]

Looking at a CCU board the device you are talking about, Q3 is a 5 volt regulator. I don't have any specific info on that device other then its function. I thought you were talking about the motor driver ICs. Q3 3 is not that close to C6 so even though it’s a little ruff looking it should be OK.

 

[D'Ecosse]

Tantalums should have been perfect! (they're not used simply because they're much more expensive.) Since it smoked so bad I suspect it was perhaps installed reversed?!

 

[Zennsx]

Try to cross reference the semiconductor on this site. if its a 5 volt reguator possibly a LM 7805? http://www.nteinc.com/
NTE Electronics, Inc. Web Site, Welcome

 

[fishtail]

Thanks for all your help and advice guys.
I've spoken with the guy who did the 'fix'. Apparently he couldn't (quickly) get replacement tantalums for all the caps. He had to use electrolitic (?spelling?) caps for the larger ones - C10 and C6. He assures me that the original replacment for C6 was installed the correct way round, and suggests that it was just a dud -they're only 18p each and you get the odd duffer. There is of course the possibility that he made a mistake, but won't own up!
Do you think that that the failure of Q3 would stop the entire CCU from working? i.e. could that 5V supply be the main one?
I no longer have any lights on the display (apart from back-lighting), and the buttons don't do anything. After the first 'fix', and letting all the smoke out of the cap, the CCU became intermittent, flickering on and off. After C6 was replaced it worked for about 5 secs then died (no somke this time). I feel a large bill coming on...
Do you have any other recommendations of what to replace/test, in addition to Q3? Can I perform any useful diagnosis with a multimeter (don't laugh - that's the extent of my electronics kit)?
One last thing that may be worth mentioning - the little fan that draws air over the in-cabin temperature sensor still runs when the CCU is plugged in, so I guess that at least some power must be getting into/out of the unit? I've also checked the fuses, and made sure that battery voltage and earth are present at the correct pins in the harness (following instructions from the Acura manual). The flow diagram in the manual says 'replace CCU with known good unit', easy for them to say...

 

[Briank]

The 5V regulator provides power for the microprocessor so if its dead the whole unit is dead. You can check for 5 volts from ground to its heat sink to see if it is working.

 

[fishtail]

Thanks very much. I'll check it out and post back.

 

[fishtail]

I've finally got around to having another look at my AC board. I checked the voltage between the regulator heat sink and ground, it was 5.1V. So I guess that Q3 is not the problem. Still no life in the CCU. I've double checked the battery and ignition supply to the unit. Is there anywhere else I can check on the board with a multimeter to diagnose the problem, or is it time to admit defeat and post it to someone who knows what they're doing (and has the necessary test kit)?

 

[Briank]

Check for continuity between the + side D7 and the + side of C14

 

[fishtail]

Hi Brian. Thanks for taking the time to help. I've checked and there is no continuity from +D7 to +C14 according to my meter. It does have continuity to +C16, but that is via a direct track. I'm testing this with the A/C board *not* connected to the car, is that right?

 

[Briank]

Hi Brian. Thanks for taking the time to help. I've checked and there is no continuity from +D7 to +C14 according to my meter. It does have continuity to +C16, but that is via a direct track. I'm testing this with the A/C board *not* connected to the car, is that right?

Yes testing out of the car is fine. Hold the board up to a strong light and look at the connection at the + side of C14.

 

[fishtail]

Wow! Are you psychic? There is a cresent of light around the +pin on C14 on the top side of the board. So.., a break in the track, does that happen often? I was only looking at the connections from D7 on the *bottom* of the board. Doh!
Sorry to be stupid, but is the fix to put some solder in the gap, or is a there a more high-tech fix that I'm going to need an expert for?

 

[Briank]

I have seen several boards: wink: with that problem. I normally put a wire from +d7 to +C14, bridging with solder will work but it’s not reliable.

 

[fishtail]

I'll try temporarily bridging it, if that works I'll get my mate with a pro soldering iron to stick a bit of wire in. I'll let you know how it goes - for the benefit of other DIYers - I'm sure I'm not going to tell Brian anything he didn't already know .
Thanks again Brian.

 

[Briank]

Fishtail glad to help.

 

[fishtail]

Soldering guy put a jumper wire in, it now works a treat. For how long, who knows, but at least the fix was free (well, it'll probably cost me a beer).
NSX Prime does it again! Thanks guys.