Transistors?

[Lazy-Ferret]

I know a couple of people on here play/work with discrete electronics.

I have a Carver Fanmaster heater in the caravan, and it has burnt out the control board.

Basically, it is old, the company that makes it no longer exists, and after extensive searching it appears no one has a copy of the cct diags, and will part with them. There is one guy who repairs them, but at a cost.

My options are
Give it a look over and try and find the fault, fixing it for a few quid
Send it off to the guy who fixes them, but it could cost up to £75 + postage, depending on what bit is faulty.
Find a second hand one, or buy a new one... which would be fine, if I had a lot of money to spare....

So, I have decided to go for option 1, then think about option 2 if I fail, and while doing those, see if I can find a second hand one at a reasonable price, go the the first part of option 3.

So, having taken it apart, the good news is, the heating elements and thermostat are all fine, and the fan motor is all working. The fault seems to lie with a rather crispy looking DB679 transistor that controls the fan motor speed.

The problem is, I do not know why that transistor felt the need to die...

In my garage, I have a few of my dads old draws full of odds and sods electronic components, so had a wade through to see if I can find one.. no such luck, but I do have a few other power transistors that he used for switching stuff in the fruit machines he made.

It is many many years since I did Transistor equivalents, so I wondered if anyone on here might know if I could get away with using a TIP121 or a TIP41B, as I have lots of them...

 

[zippy656]

http://www.caravantech-shop.co.uk/p.../heater-spares/carver-fanmaster-slider-switch

Um this the bit thats gone?

 

[Lazy-Ferret]

http://www.caravantech-shop.co.uk/p.../heater-spares/carver-fanmaster-slider-switch

Um this the bit thats gone?

No, that is different to ours...

We have the unit that has a dial, and 5 tiny LED's and 2 push buttons on the control unit.

The board that looks like it has gone, it the one fixed to the aluminium heater housing behind the fire, and looks like this.

 

[zippy656]

Ok
will keep, looking

Will look in the stores monday too

 

[rustic]

Can you confirm the part no. of the transistor

DB 679, or BD 679


Here is a link for BD 679
http://uk.farnell.com/stmicroelectronics/bd679/darlington-transistor-to-126/dp/9946454


The transistor is not a 220 type package, can you take ALL the details of the transistor as written on it. also sketch the circuit around the transistor, and any other components around the area.
A circuit diagram would help, then you can try equivilent transistors.

The transistors suggested may not be suitable, as it depends on how the transistor in the circuit is used.

As you say, it could be a fault outside the circuit board that has caused the transistor to blow, or the transistor has failed over a long time on a particular setting, causing overheating of the transistor.

EDIT...


have a look at this thread, and similar pictures of the circuit board...

http://www.edaboard.com/thread239766.html


Is it the same.

 

[Lazy-Ferret]

Can you confirm the part no. of the transistor

DB 679, or BD 679


Here is a link for BD 679
http://uk.farnell.com/stmicroelectronics/bd679/darlington-transistor-to-126/dp/9946454


The transistor is not a 220 type package, can you take ALL the details of the transistor as written on it. also sketch the circuit around the transistor, and any other components around the area.
A circuit diagram would help, then you can try equivilent transistors.

The transistors suggested may not be suitable, as it depends on how the transistor in the circuit is used.

As you say, it could be a fault outside the circuit board that has caused the transistor to blow, or the transistor has failed over a long time on a particular setting, causing overheating of the transistor.

EDIT...


have a look at this thread, and similar pictures of the circuit board...

http://www.edaboard.com/thread239766.html


Is it the same.

Hi, yes it is the BD679.. that is the problem with being dyslexic... Sorry..

It is in a TO126 case, but it is mounted on a HeatSinc, so I can swap legs over easy enough to suit a different pin out.

and Yes it is the same board as in the link.

Basically, it is used as a switch to turn on a 12V fan motor, with Collector connected to 12v, Emitter feeding motor, and a Diode and cap to ground.

Base is controlled by a surface mount chip with a few surface mount components, but I will need the magnifying glass to see the values, if they are on them. The problem is, some of the tracks run under components, and there are "feed throughs" under them as well, so they are hard to follow.

I have spent about 3 weeks, on and off looking for the CCT diags, no one seems to be able to find them.

 

[rustic]

Try the Farnell link, and if you order one, you may find like I did, that you get free delivery even on a one off.

So it could be a cheap fix!:nenau just over a pound...

So had the heater worked before with all functions as normal?
What were the events leading up to its failure?



best regards, Rustic

 

[Lazy-Ferret]

Try the Farnell link, and if you order one, you may find like I did, that you get free delivery even on a one off.

So it could be a cheap fix!:nenau just over a pound...

So had the heater worked before with all functions as normal?
What were the events leading up to its failure?



best regards, Rustic

Cheers, I just ordered 2 off of Ebay for £1.65 inc P&P. Fingers crossed it was just a time related failure.

Basically the Van is a 1996, and this is OEM fitted, so it is 17 years old. About 6 years ago the bearings on the motor dried out, and it squealed continually, so I changed the motor. It was fine until this year, when it did it again. I read up on the motor, and it seems that as it is used infrequently, the bearings dry out, as they need regular running to generate the heat to make the oil flow down.

Since it is such a pig to take out of the van, when I stripped it down this time, I rigged up a couple of 3mm brass tubes that run down to the bearings, so I could oil it in situ, I soaked the bearing and put it all back together as there was no play, and one lubricated it seemed to work perfectly.

It worked fine for the first week of our holiday.

I am hoping that the failure is a result of the over work it had when the motor was running dry, and then the fact that it was so cold when we were away at Christmas, we had the heating on almost continually, but since the heater is so efficient, it spends most of it's time on the slow setting, which is of course when the transistor is working hardest.

 

[rustic]

logic seems to point that way.

Most high volume products tend to use components that will just manage to do the job, anyway, circuit must have been well designed, as it lasted 17 years, so the extra load could have done it.

Post again when you try the replacement transistors.

best of luck,
Rustic

 

[briggie]

talking of transistors .......... if anyone can aquire a couple of SRF7043's , id be eternally gratefull :thumb2

 

[solarman216]

you should have said when you were here, I have stacks of transistors, some very old wire ended audio ones, have not looked through for BD679 but could well have one or two, Rick

 

[solarman216]

talking of transistors .......... if anyone can aquire a couple of SRF7043's , id be eternally gratefull :thumb2

what do they do Pete and what package are they, I will have a look, most of mine are in plastic tubs by shape so do not want to waste time with a glass looking for numbers if I am looking at the wrong shape

 

[briggie]

what do they do Pete and what package are they, I will have a look, most of mine are in plastic tubs by shape so do not want to waste time with a glass looking for numbers if I am looking at the wrong shape

they are mosfets rick , high power uhf / vhf

 

[briggie]

look like the pic below .....

http://www.google.co.uk/imgres?imgu...6N-qY1AWp5YDQAw&sqi=2&ved=0CEgQ9QEwBA&dur=342

 

[solarman216]

they are mosfets rick , high power uhf / vhf

then not so likely I will have them, have you tried Farnell? if not I have an account and can try a search but have not used it for a while so will have to find my password, Rick

 

[briggie]

then not so likely I will have them, have you tried Farnell? if not I have an account and can try a search but have not used it for a while so will have to find my password, Rick

as rare as hens teeth rick , i doubt if farnell will have them

 

[solarman216]

http://parts.nowcomponents.com/

try here Pete it is listed, Rick

 

[briggie]

cheers rick :thumb2 , thats the motorola copy , its a sunstitute ( 80% as efficient as the original ) , but it will work :thumb2:thumb2 ..... trouble is its usbid , horrendously expensive and have a minimum order :doh

 

[rustic]

look like the pic below .....

http://www.google.co.uk/imgres?imgu...6N-qY1AWp5YDQAw&sqi=2&ved=0CEgQ9QEwBA&dur=342

this might help.. for why theybsometimes blow.

http://www.hampedia.net/yaesu/ft-100d-srf-7043-replacements.php

 

[solarman216]

Yes been having a look round, seems you are out of luck at a reasonable price, the SK702 works but at lower power but seems hardy, you could try Bob at KC3V0 he has used MRF1570 after minor mods, so worth a chat, Rick