Re: Some issues with the Shandon HistoCentre 2. Advice wanted

"Bob Chiovetti" <rchiovetti@xxxxxxxxx> wrote in message
news:28b1bfbc-b0a6-4b8e-a604-8a6b6c6d717b@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Mar 17, 12:26 pm, Bob Chiovetti <rchiove...@xxxxxxxxx> wrote:
On Mar 16, 6:31 am, "Y" <a...@xxx> wrote:



Hi all,

I recently bought a second hand Shandon HistoCentre 2 and I have some
minor
problems with it:

1. The hotplate of the unit only warms to about 52°C with T° regulation
in
it's highest setting. As I use a paraffin with MP 56°C - 58°C (Carl Roth
Rotiplast) it would be nice to have a hotplate that will keep my molten
paraffin somewhat hotter. Any suggestions on a solution for this? Is
there
an internal regulation or a known tweak to solve this?

2. Something very odd: the electronic valve of the paraffin dispenser is
kept warm by a few resistors mounted on it. It works fine. The outles
itself, meaning the small external piece of piping protrubing from the
machine were the paraffin leaves isn't, except for the heat produced by
two
tiny lightbulbs, intended to lighten the hotplate. As I experenced this
morning, this means: no light, nada paraffin! Really! I can't imagine
that
such expensive equipment depends on the action of 2 cheap lightbulbs! Or
am
I missing something, here? That is I suppose, except for the price of
the
bulbs Shandon will charge...

Thanks in advance for your advice!

Y.

Maybe the two problems are related. The paraffin container should
easily get up to 65-70 degrees C. I don't know about this particular
model, but many embedding centers use band heaters to heat the
paraffin container and the dispensing tube. These heaters have an
adhesive back on them, or sometimes they are glued to the part to be
heated, usually with a high-temp silicone adhesive (something like RTV
-- it's usually red in color).

It sounds like one or more of the heating elements (band heaters?) are
not working. If a heater on the paraffin reservoir or a heater that
heats both the paraffin reservoir and the dispensing tube died, this
would explain your problem.

First thing: Are there fuses on the back of the machine? If so, check
them. You could also check the wiring inside if you care to
disassemble the instrument. It sounds like either a blown fuse or a
dead heater. Band heaters are difficult to replace, since they're
glued tightly to the part to be heated. If it is a bad heater, look
for a manufacturer / part number on the heater before you start
scraping it off.

Hope this helps. Let us know what you find!

Bob Chiovetti
Southwest Precision Instruments
swpinet dot com

Oops, I misread your message. You're having temperature problems with
the hot plate surface, *not* the paraffin reservoir, correct? But the
same rule would apply, I think (a bad heater or a blown fuse.) The
hot plate should have no problems reaching 65-70 degrees C.

If the paraffin dispensing tube is hot to the touch, its heater should
be working OK. I wonder if the temperature of the dispensing tube is
somehow related to the temperature of the paraffin reservoir? Do you
set the temp of the paraffin reservoir about 2-3 degrees C above the
melting point of the paraffin? Try that, and see if the dispenser
starts working. Maybe there's just not quite enough heat being
conducted to the end of the tube.

Bob Chiovetti
Southwest Precision Instruments
swpinet dot com

Hi Bob,

Thanks for your advice.

As I use a paraffin melting point 56-58°C I had set the heater of the
paraffin reservoir at 60°C. Apearantly you are right as augmenting the T° to
62°C solves the problem. T° regulation of both paraffin reservoir and
specimen reservoir works fine as does the cooling plate of the machine.

The problem of the hot plate isn't solved (yet) and that one is very
important for me, as I have to orientate and embedd multiple samples in one
block.

Now, judging from the behaviour of a few blinking LED's on the front side of
the machine, the heaters are powered by a time - proportional regulation, I
suppose using triacs or thyristors. The LED indicating the hotplate keeps
burning in the highest setting of the regulator, meaning that the heater (or
the gate of the triac/thyristor) is constantly powered. In that highest
setting, the highest T° I measured was 53.4°C, making embedding very
problematic... In a lower setting the led blinks, meaning that -as a lower
T° is wanted - the heaters aren't powered using a 100% ON cycle. So judging
from the LED, the T° regulation seems to work as it should. It seems that
either a fuse of the power circuit of the heaters has blown, or a
triac/thyristor is dead or a heater is dead. There are now fuses visible on
the outside of the machine, but it's not that strange that these would be
located somewhere inside. I'll try to dismantle the machine tommorrow to
have a look inside.

By the way: just a few hours ago, at nearly the end of it's cycle (last
paraffin bath) my tissue processor, an old caroussel type Shandon 2LE, gave
up :-))). I could still use it in manual mode, so I managed to save my
samples :-).

Yvan.





.

Relevant Pages