ALC68 strip down & clean - Help please

[smogthemog]

Can someone help me please that maybe has one of these cards or has a diagram of the logic card that can easily be read?
The Logic card diags that are floating around on the net are not clear enough to see the writing

Across the top of the board there are several metal can devices.
From left to right, top row:

1) 2N2222A transistor
2) ? (Mine has an LM311H) ???? This has been replaced at some stage and I feel is faulty!
3) ? (Mine has an LM741CH)
4) LM555CH timer

5) slightly under the top row of devices: CA6741CT (possible LM741CH?????)

Thanks
Jim

[smogthemog]

Can anyone help me here, im really struggling with this ALC68B Logic card.
I have a square wave from the 555 timer which feeds into V214 through R217 but that's as far as it gets, although on the scope, it changes from a square wave to a saw tooth wave before it gets there???
I had an LM311H in there at V214 location (before I revamped the PSU and had the fry up ) but have replaced it with a LM311N and wired accordingly but there is NO output from this Comparator. All the voltages around it seem ok, GND, VCC, VEE etc etc but I am not sure what sort of voltage should be on the +in pin, from R218??
The -in pin has the sawtooth wave on it from the oscillator at around 1v PtoPeak.
The - & +15v rails all seem there too.
Any questions will be answered and help appreciated please

[mojo]

Hi,

I'm already following your thread for a quite long time now. Nice work *respect*.

Regarding the issues with the "logic card" it seems that V214 is a "differential amplifier" allowing the signal from the remote control (via E/F) to somehow modulate/control the signal comming from the NE555. Guess also the saw tooth signal is fine because of the RC filter (C208 and R235) and V209. What happens if you power the U+ (signal from -5V to 5V) of V214? Does the signal of V214 changes? May this is the faulty part...

Have also seen some similar logic card offered on eBay ("Eil 4000 Logigkarte"). Looks quite similar (but brand new :-).

Do you have some plot of the saw tooth signal?

-mo-

[smogthemog]

Thanks for the kudo's and thanks for your help

Not in my shed tonight as I am kid sitting so I cannot get the plot for you - I take it you mean a photo of the front of the scope?


Quote= What happens if you power the U+ (signal from -5V to 5V) of V214? Does the signal of V214 changes?

Can you explain this a little further please, I don't quite understand what you mean?

I don't actually know what V214 should be. As I mentioned, I had a metal can LM311H in there at the V214 location (before I revamped the PSU and had the fry up), this is not the original component as it only had 8 pins where the board actually has 10 holes in it?? but have replaced it with a LM311N and wired accordingly. This is why I was asking if anyone knew what was supposed to go in there originally.

Thanks
Jim

[mojo]

Hi Jim,

there should be some signal from V214. If V- has some signal (saw tooth) and V+ is on ground level there should be some output on Vout. Are you sure the "new" V214 is working?

Some photo of the scope plot of V- and Vout would be helpful. Regarding a LM311H or LM311N I guess there's no difference. Both are high speed comparators.

-mo-

[smogthemog]

I don't think there is anything from V214 on the output pin, no traceable signal anyway. I am wondering whether to remove & check all the components around it? It's certainly odd. I purchased 2x LM311N's and they are both the same. There is something silly going on here, something I am overlooking, something simple.
I took my scope to work today and have forgotten to bring it home with me but I will get those photo's for you tomorrow night for definite, sorry for the delay

Edit - I am going to remove the caps and check them also.

[mojo]

Would also check if all pins of the opamp V214 are connected properly (may be pinout is different). Also check carefully for a solder bridge etc.

[mixedgas]

UA736 had a few extra bias inputs for its output stage. I imagine you might need to add a "pull up" or "pull down" resistor to LM311s output to make it the same as the old chip.

The 555 and integrator generates a ramp at the switching supply frequency. The signal is sent to the comparator to generate pulse width modulation for the drive card.

What I did when I worked on these was get a card edge connector and apply +/-12V to it, so I could run the card outside the laser and "fake out" the control signals till I was sure I had good results on the scope.

The Mod to the PSU involves adding a 100K ohm potentiometer and a few other parts across place of the inout opto-coupler. The optocoupler itself was carefully driven by the medical board to act as a variable resistance. To do this they had a identical optocoupler on the medical board to form a feedback loop.

I will email Bruce and see if he still has the modification schematics. I sold my Meditech long ago.

I will also scan in the 68B schematic today. I will be on the road for one month, and if I dont help you now, I will not have access to my docs.

Steve

[mixedgas]

attached

Smog, I had the WHOLE schematic converted to a professional PDF. Its 25 megabytes. Find a way for me to upload it to you.

Attached is a clipped, distorted view of the logic card, until we can get you the whole professional scan.

Steve

[smogthemog]

A huge thank you to you both for your help!!!

OK, I have taken some measurements tonight. The first picture was the signal at R235 end of R213 from the 555 to V209.
The scope settings where 50mV per div @ 20uS per div.
The second picture was V214 end of R217 from V209 - 2V per div @ 20uS per div.

Voltages on the pins of V214, the LM311H
1 - 0v
2 - +12v
3 - +0.02v
4 - -13.8v
5 - +13.29v
6 - +13.29v
7 - +13.33v
8 - +13.4v

The LM311N pins to respective holes in the board, or where the UA736 should be, correspond as follows:
1 to hole 8
2 to hole 2
3 to hole 3
4 to hole 7
5 NC
6 NC
7 to hole 9
8 to hole 10

http://www.ti.com/lit/ds/symlink/lm311-n.pdf

Pinout's on page 20 of the .PDF

I am able to run the board in situe as I have the HV disconnected for fault finding purposes.
Please remember this worked OK with the LM311H in situe prior to the smoke from the Driver card, something backtracked from the driver card incident to damage the logic card

Are you sure Steve it was a UA736 in there and not a UA734? I can find no reference to a 736 but can to a 734 and it seems to match the pinout's on the diagram?

1 - - IN
2 NC
3 - Offset Null
4 - Offset Null
5 - -V
6 - GND
7 - OUT
8 - Pull Up Res
9 - +V
10 - + IN

- - - Updated - - -

AS for the 25Mb????? I have NO idea