View Full Version : C.Itoh CIT 100 Maintenance Manual

March 11th, 2018, 06:07 AM
There doesn't seem to be any online.
Lots of User Manual copies, no service/maintenance info.
Anyone have one?!

March 11th, 2018, 11:13 AM
Yes this is correct, I dont have one and just searched around on the /net and dont find one. so yes no maint is available to the best of my knowledge


March 11th, 2018, 12:15 PM
Here's a thought.

The CIT-100 is essentially a shameless knockoff of the VT100, right down to being able to interchange keyboards, AFAIK. There's plenty of good maintenance info on the DEC product; perhaps it would be a help?

We used several of the CIT 220 terminals back in the day--I really liked them.

Al Kossow
March 11th, 2018, 12:17 PM
Here's a thought.

The CIT-100 is essentially a shameless knockoff of the VT100, right down to being able to interchange keyboards, AFAIK. There's plenty of good maintenance info on the DEC product; perhaps it would be a help?

We used several of the CIT 220 terminals back in the day--I really liked them.

some pictures of the board in the CIT would quickly determine how close the circuitry is.
it's not going to be exact, since there are custom video asics in a vt10x

March 11th, 2018, 01:57 PM
Thanks folks I'll get some pics uploaded.
Yes its a knock off but perhaps not terribly interchangeable, as that is the chatter
on the web, but not confirmed.
I have a VT102 to compare to if thats the case.
I was hoping this request might shake loose someone who has
the manual leading to it getting scanned and made available.

March 11th, 2018, 07:01 PM
OK here's a bunch of pics.

A short synopsis: Had two CIT101's that I pulled out of the basement of MOS Technology during that recent cleanout.
These were in rough shape, one was complete but the screen was knocked in, the other
was missing the top cover, had worse water damage, but had an intact tube albeit with some burnin. Decided to try to make one good terminal. I happen to have a CIT101 kbd.

Power supply 5v and 12v checked out. I reseated the socketed ICs and gave it a try.
The keyboard indicated one fault detected in post. Not bad!
Tube did not heat up; no glow.
I swapped for the other video board, still no glow.
Don't know what's up with that, 12v is getting to the video board.

I attached a composite monitor to the back panel video out. There was signs of life there but not
well formed video. Close examination of the board showed that I had bent some pins
on the NV memory part. Fixed that, still no good video. Then found pins got broken
on two other ICs that were corroded. Fixed that. The video change a bit, still not right,
but the POST now ran clean!

When I turn on the terminal, I can see some almost well formed video picture before it
breaks up. I think the display is trying to show a cursor but the pixels are strewn across and down
the screen. I have some confidence that the 8085 micro is doing a lot of stuff that is "right".
I'm going to scope this soon.

The only thing I can think of to do next is replace the few electrolytic caps on the board.
They cluster around some transistors, which might be the video related.

That's where I'm at.

March 11th, 2018, 09:21 PM
Video *was* like this.

I then noticed that the video tracked going in and out of setup, a good sign!
Managed to hsync the monitor with the knob and got:
What a thrill.
It was short lived. The hsync changed and lock was lost an unrecoverable.
Thought maybe it was the monitor, so I tried another with the same results.

The scope looks like this, 5v & 50uS per div. (10x probe),.
Those hsyncs are 112uS apart... I think that's wrong.

I also discovered that the tube is glowing- I had to turn out the lights to see it.
But there is nothing on the screen... that's something I'll tackle when the composite video out
is right on the back panel.

That's all for today, all in all not bad progress.

March 12th, 2018, 08:59 AM
Are you getting any anode high voltage to the CRT?

March 12th, 2018, 09:50 AM
Thanks... I need to find out...
I'm a software guy and half a digital hardware guy... so I don't know what to measure there
without some web research on the methods for such measurements around the CRT.

March 12th, 2018, 10:22 AM
Just be careful--I doubt that the anode HV has enough current to kill you, but a bit of carelessness could be unpleasant. Bad FBTs aren't unusual in the CRT world; the same goes for bad HOTs. Start with the horizontal output transistor first.

March 12th, 2018, 11:51 AM
Will do. I'm reading up on the FBT and HOT.

Any comments about the scope photo of the composite video?
I figure I have to trace back to the video generation and see why the timing and
amplitude are off.

The video board has some "oversized" electrolytic caps- 10uf 25v and 4.7uf 25v- over 1 inch high
and about 1/2 inch diameter. Is there a reason for this? My replacements
(considering doing a recap) would be really tiny by comparison.

Is this thing worth it?!

March 12th, 2018, 11:57 AM
Consider the age of the board. Capacitors have steadily gotten smaller over the years as technology has improved.

You can always get a larger sized modern caps by raising the WV on the replacement. So, instead of 25V, take a look at 50V ones.

The antique radio buffs sometimes get around this issue by gutting the innards of the old cap and using the "can" to conceal a modern unit.

March 12th, 2018, 12:27 PM
OK thanks.
The size of other caps on the board are on par with moderns.
The size difference on these two was so sever I thought maybe they had a special property.
For example, ultra low ESR or something.
I'm not concerned with the appearance so I'll replace them at will.

March 12th, 2018, 01:19 PM
Do check to see that they're not non-polarized caps; i.e. the + and/or - should be very clearly marked. If they're non-polar and you substitute a regular polarized one, you'll end up releasing magic smoke.

Al Kossow
March 12th, 2018, 05:07 PM
Thanks folks I'll get some pics uploaded.

do you have any way to dump the eproms?

March 12th, 2018, 06:36 PM
Yessir! I did dump the EPROMs. The contents look good. There are ASCII strings in the
first three, the forth one has nothing readable, I hope that's because its all code. Hard to know.
Let me know where you would like them sent.
When my attention turns to the non-prime board, which is very different from my prime board,
I'll get those ROMs too.

The original caps were in fact not clearly marked, but the board was.
You can see an orignal board (above) compared with my recap, lower.
See my dwarf caps in the upper left of the lower board.
There were + marks on the board.

I made some progress. The flyback is located on its own module.
On both machines, the flyback diode was practically dust. The cap there was
broken on the parts machine. I replace the diode with a beefy one I had handy-
may not be the best/right specs but I figured it would be OK for starters.
I am looking for similar flyback design to get a diode part number off of.
(Cause I don't have the maintenance manual to know the right one!)
The module on the parts machine also had a capacitor with one leg detached.
Clearly these components get some abuse.

So after recapping the video board, the flyback module and replacing that diode,
I now have high voltage generation. I could hear it. But I heard two SNAPS that I could
not locate the source of. Unfortunately I was not right over the unit to get a sense of it.
I *think* it was from the video board.
I powered down, looked around, and next power up, no snaps.
I guess I blew something but noting looks fried.
There was never any image or beam on the CRT.

I discharged the tube to continue diagnosing, and it was definitely charged- SNAP!
That's progress but I really hoped it was going to work this time, now I have to dig
deeper into measurements I don't know how to do. yet.

When I got the board out, I noticed the transistor with the heatsink in the lower left was warm,
the similar one on the upper right was cold. Cold that might mean that part of the circuit isn't doing

QUESTION: If I have HV being generated, what can I assume in the path is good?
I have to admit, out of the transistors on the board, I can't say I definitely know which
one is the HOT.

March 12th, 2018, 08:49 PM
Well, you're getting HV, so it means that the FBT and HOT are operating.

But those itty-bitty replacement caps look very wrong. Got any shots of the markings on the original? It may be time to do some research.

March 12th, 2018, 10:28 PM
That's good news! Now why no trace on the screen. Tube bad? Video input isn't any good?
Always blanked? These caps?
Here they are.

Is it essentially a composite signal that interfaces with the video section?

Al Kossow
March 13th, 2018, 07:10 AM
Yessir! I did dump the EPROMs. The contents look good. There are ASCII strings in the
first three, the forth one has nothing readable, I hope that's because its all code. Hard to know.
Let me know where you would like them sent.

You should also try to dump the 2332 character generator rom.
Emailing them would be easiest (will PM the adr)

March 13th, 2018, 07:28 AM
OK will get that too.

March 13th, 2018, 07:44 AM
The troubling thing about the caps is that there's no polarity marking on them. To me that says, irrespective of the PCB markings, that they must be nonpolar, which would account for their size. Here's what a 50V 4.7uF nonpolar Elna looks like--note the absence of polarity markings--and that it's marked with the CE(BP) notation--you might want to see what CE(BP) means to Elna. (To the best pf my determination, CE=cerafine series and BP=bipolar. These were bipolar caps treasured for their use in audio crossovers. They're no longer made, but Elna has an equivalent bipolar audio series, as do other manufacturers).


Those capacitor markings aren't put there for decoration! :)

March 13th, 2018, 10:17 AM
That's excellent sleuthing. Probably the two SNAPS I heard were the two offending caps I
installed. :) I'll further research, and obtain some like caps. I do have 4.7uF non polar-
but they are just as small as the polarized ones I used.
I removed both pairs of ELNA caps from the two video boards and measured them,
and reinstalled the best back into the prime board. (which were the two that came off of it).
There was also a 33uf 250v cap that was close to 20% high, I didn't have a direct replacement
and put in a 47uF 250v cap.
With that all done, still no difference in the display.
If I get to it, I'm going to scope the incoming signals and see if they are reasonable,
and I guess follow the path inward from there.

March 13th, 2018, 10:30 AM
>Those capacitor markings aren't put there for decoration!

So true. Should pay closer attention to markings!

March 13th, 2018, 10:51 AM
Ordered some ELNA CE BP audio caps form hong kong.

March 13th, 2018, 11:05 AM
As far as not getting an image, you might troll some of the documents on bitsavers wtih regard to terminals in general. At the CRT level, they all operate pretty much the same, so that voltage and waveform specs should be in the same ballpark.