Erm, ok, I see where a problem is! Q852 pins measure as follows:
1: -24.8 v 2: -0v 3: -26.9 (pin numbers as looking from front of board). I don't honestly understand transistors so I'm not sure what this tells us. But I can say for sure this is where the voltage stops getting thru!
R852 and R853 measure 0vdc.
edit: there's continuity between the middle pin of the transistor (Q852) and the two 47ohm resistors that feed the display (R852 and R853). So either that transistor is broken, or I'm missing some crucial knowledge...
Where to next?
1: -24.8 v 2: -0v 3: -26.9 (pin numbers as looking from front of board). I don't honestly understand transistors so I'm not sure what this tells us. But I can say for sure this is where the voltage stops getting thru!
R852 and R853 measure 0vdc.
edit: there's continuity between the middle pin of the transistor (Q852) and the two 47ohm resistors that feed the display (R852 and R853). So either that transistor is broken, or I'm missing some crucial knowledge...
Where to next?
Evening Simon!
Do you have a spare 7918 to test it? Or a 7915? A regulator should always deliver the voltage it is supposed to, so I think it is a suspect. Also check if that ground-pin is really shorted to 0V now, through the wire link. If the regulator's ground-pin is lifted, the output voltage will start floating and become more negative.
The middle pin of Q852 is the collector, and that's connected to R852/853. So the continuity you measure is supposed to be there, it's a PCB track
. Don't you have the board lay-out?
But it shouldn't be 0V there...
Ray.
Do you have a spare 7918 to test it? Or a 7915? A regulator should always deliver the voltage it is supposed to, so I think it is a suspect. Also check if that ground-pin is really shorted to 0V now, through the wire link. If the regulator's ground-pin is lifted, the output voltage will start floating and become more negative.
The middle pin of Q852 is the collector, and that's connected to R852/853. So the continuity you measure is supposed to be there, it's a PCB track
. Don't you have the board lay-out?But it shouldn't be 0V there...
Ray.
6h5c said:Evening Simon!
Do you have a spare 7918 to test it? Or a 7915? A regulator should always deliver the voltage it is supposed to, so I think it is a suspect. Also check if that ground-pin is really shorted to 0V now, through the wire link. If the regulator's ground-pin is lifted, the output voltage will start floating and become more negative.
The middle pin of Q852 is the collector, and that's connected to R852/853. So the continuity you measure is supposed to be there, it's a PCB track
But it shouldn't be 0V there...
Ray.
Ray,
Annoyingly I don't seem to have any 7918 or 15
It does seem like the reg could be dodgy, but the voltage into it is off too I think, but you're surely right: it's either the ground of the reg or the reg is bust! Makes sense.I do have the service manual, and I've printed it. But I'm yet to learn about transistors. I have no formal education in electronics. I can see it should be about -19v where those resistors are.
Thanks for your time and help.
Simon
6h5c said:
That's not entirely correct Andy.....
gy21,
If you want to replace the 2114 with an AD8620, then these adapters will do fine, since the 8620 is also a dual opamp.
Regards,
Ray.
Thanks Ray, I will try to order some of those, meanwhile I will insert an opa2134 to hear what that sounds like.
SimontY said:Ray,
Annoyingly I don't seem to have any 7918 or 15
Simon
You're welcome!
It indeed seems that the input voltage is not correct, but that is a raw supply, and it will vary with load current. So if the display doesn't get anything, it would make sense that it's higher (more negative) because there's no load. The regulator is able to handle upto -40V input, so that's o.k. The output voltage however, should be -18V +/-4% for this type of regulator. But....in the players here they are 79M18A, and the "A" version has an even tighter tolerance of only 2%. So 26.4V is way off
.Regards,
Ray.
6h5c said:
You're welcome!
It indeed seems that the input voltage is not correct, but that is a raw supply, and it will vary with load current. So if the display doesn't get anything, it would make sense that it's higher (more negative) because there's no load. The regulator is able to handle upto -40V input, so that's o.k. The output voltage however, should be -18V +/-4% for this type of regulator. But....in the players here they are 79M18A, and the "A" version has an even tighter tolerance of only 2%. So 26.4V is way off
Regards,
Ray.
Morning Ray,
Actually this reg was once swapped because I accidentally broke it (shorted 2 pins). So it's not the original. It's actually L7918CV if that means anything useful.
The ground pin is definately connected to the wire jumper, which is in turn connected solidly to ground.
Simon
Simon
check the datasheet for pinout
http://www.datasheetcatalog.com/datasheets_pdf/L/7/9/1/L7918CV.shtml
if ok
then enough voltage in to sustain reg's voltage ( needs 2volt extra)
if ok and still too much voltage out from reg then the regs no good
if the voltage was lower(closer to 0) then maybe something drawing to much current, but you would notice the reg getting hot.
if too much voltage (over reg's rated out) and ground ok, then reg's no good.
allan
check the datasheet for pinout
http://www.datasheetcatalog.com/datasheets_pdf/L/7/9/1/L7918CV.shtml
if ok
then enough voltage in to sustain reg's voltage ( needs 2volt extra)
if ok and still too much voltage out from reg then the regs no good
if the voltage was lower(closer to 0) then maybe something drawing to much current, but you would notice the reg getting hot.
if too much voltage (over reg's rated out) and ground ok, then reg's no good.
allan
rowemeister said:Actually.... use this sch and over type the voltages on as many points as possible and post it back on here. That should get your problem sorted quicker
been looking for the schematic thanks andy.
Q851 -18v reg lower to -24v with zener. why?
why not just use -24v reg
allan
ps my schematic is around here somewhere
awpagan said:
been looking for the schematic thanks andy.
Q851 -18v reg lower to -24v with zener. why?
why not just use -24v reg
allan
ps my schematic is around here somewhere
Well Geoff
I presume it gives more scope for adjustment by using different zener values in different players, zener diodes are cheaper than regs so when you sell millions of units you save alot of money.
Brent
rowemeister said:
Well Geoff
I presume it gives more scope for adjustment by using different zener values in different players, zener diodes are cheaper than regs so when you sell millions of units you save alot of money.
Brent
or maybe they had a lot -18v reg's sitting around
or the -24v reg wasn't available yet
or someone did an ooops
(this one i like)allan