Re: HOT keeps breaking down

"petrus bitbyter" <pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx> schreef in
bericht news:42c8350b$0$776$3a628fcd@xxxxxxxxxxxxxxxxxxxxxxxxxx
>
> "Rene" <invalid@xxxxxxxxxxx> schreef in bericht
> news:EaqdnTAs0Oa2QFrfRVnyjQ@xxxxxxxxxxxxxx
>> "Inty" <inty.the.best@xxxxxxxx> schreef in bericht
>> news:Kl9xe.22344$h5.988881@xxxxxxxxxxxxxxx
>>>
>>> "Rene" <invalid@xxxxxxxxxxx> ha scritto nel messaggio
>>> news:wYGdnXfB448_mljfRVnygg@xxxxxxxxxxxxxx
>>>
>>>> store gave me a BU1508DX instead of a BU1506DX which was not in stock
>>>> (but
>>> SPPPPPPRRRRRRRRRRRRRRRR!!!!T
>>> There's something that isn't ugual on those two xistors... they aren't
>>> interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of
>>> 5.0V
>>> and there are some diverse parameters...
>>
>> Dear Inky,
>>
>> Very funny, in another store they also said that their computer proposed
>> the 1508 as a 1:1 replacement. I do not trust their computers. Well, I
>> mean, I do not trust the people who put this info into their computers.
>> I ordered a new LOPT and also two 1506's. When I have results, I will
>> post them here.
>>
>> Thank You very much for replying!
>>
>> Sincerely,
>> Rene
>>
>
>
> Comparing the datasheets of both types reveals they virtually be the same
> although the 1508s specs are slightly better. The VCESAT Inky mentioned is
> a maximum so worst case. The actual VCESAT may be below 1V for both types.
>
> The LOPT is a pretty expensive device. You can find many tips for checking
> the it at:
> http://repairfaq.ece.drexel.edu/sam/flytest.htm
> a relatively easy to build tool at:
> http://members.ozemail.com.au/~bobpar/fbt.htm

Thanks for the links, I already ordered a new one at Lejos (30 euro's). Off
course they are useful for the future and the schematic of the tester is
great! (A pity You and Maarten did not reply to the post in the Dutch group,
I had been really hoping for that.)

> Although the LOPT might be defective, the control signal of the HOT is at
> least as suspective. You hardly can check this out without an
> oscilloscope. You need to check the frequency and the pulsewidth. The
> pulsehight may give you an idea whether or not the pulse has enough power
> to drive the HOT correctly. A positive DC level (p. e. caused by a leaky
> driver transformer) will be disastrous for the HOT. For maximum certainty
> you'll need the specs of the manufacturer.

Hi,

I have the official service doc in which the shape of the signal on the
transformer that drivers the base of the HOT is displayed. I do have a
scope, I wrote that in the Dutch thread (sorry for multiposting instead of
crossposting, I normally never do that, but then, these groups have
different languages). The picture is not exactly the same. Unfortunately I
did not know where to get the mass for the scope, I chose to measure over
the transformer, as the side of it that is not connected to the base of the
HOT, is connected to "gnd 1". I hope the picture I get, is OK then (can't
think of a reason why not, but then, I am not an expert). The test point is
called "L2". Frequency and pulse-width are OK, the shape is not exactly the
same. I will have to check again for the DC-component as I was not aware of
it's importance when I was testing, I do understand it now. If the peak
level is not as high as on the doc (I remember it was lower because the
scope was to be put in 20 V/div mode while mine's maximum is only 10V/Div),
can it cause the HOT to die?

Thanks very much for replying.

Greetings,
Rene


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