View Full Version : Help needed with a "19 Zenith 9-291 chassis (SB1923W Space Command set, 1985 build)


>QUAD<
01-18-2016, 02:53 AM
Hello

This is my first post on the VideoKarma forums, I have been posting on AudioKarma in the past but never before here,
I've been browsing the forums on here quite a few times though.

So, a buddy of mine picked up this "19 Zenith Space Command set (model SB1923W) from a Goodwill this December,
fascinated by "how cool things would look on a retro CRT set", and a short while later
(when the fascination went away and he went back to his "40 flat panel) he passed the Zenith to me.

While checking it out at his place I was surprised that the image on the set was quite good and the CRT still looking strong,
although the set did need some adjustments (focus, bit of convergence, minor color adjustment, yoke angle, and horiz. width).

Having done most of the things I just mentioned, I am now left with the overly wide picture, for which there is obviously no adjustment.
Suspecting the B+ being out of range, I went through the power supply board and measured the B+ at what appears to be 116V,
I have looked at all of the resistors on the power supply board
to see if any have drifted, and all look fine (the sand blocks are all still within %5 at worst),
there was one resistor that was marked 19K (by the color bars) sitting across the filter cap that drifted to 16.8k but replacing it didn't help.
Electrolytics on PS board all test fine.
The power supply module uses the STR (TO-3 type) power regulator.
The set doesn't appear to have had any service done to it except for one service sticker on the back dating to '86.

So, is anyone familiar with this chassis? I tried looking it up on google, and managed to find a list of models that use this chassis
(oddly enough my set isn't mentioned in that list), but not much useful info other than that.

If anyone has the schematics diagram, or is willing to help me get this set working as it should, I would really appreciate that.
I am going to keep it, upgrading a 1982 "13 Hitachi set I have right now (won't be getting rid of the Hitachi either,
but I would love to have a bigger screen to enjoy my recently acquired NES on :music:)

Here are a few pics, the set is in quite a nice shape, with only a couple of small scuffs overall,
the inside was very dusty but looks great now after a thorough cleaning.

Electronic M
01-18-2016, 03:11 AM
Some over-scan is normal for CRT TVs....It may very well be designed to produce the amount of over-scan you see.

zeno
01-18-2016, 06:35 PM
Very few of these came back for service. Check the STR first.
Marking tells the voltage out so an SRT30130 is 130V
STR30125 is 125V etc. One of the big bricks usually will
have raw B+ & other end regulated B+.
If the regulator is OK its a hoz problem or normal overscan.
STR's loved to short but almost always cause shut down
& or hum bars.

73 Zeno:smoke:

>QUAD<
01-18-2016, 07:08 PM
I'd understand if that would have been a bit of overscan, but the picture here is stretched by at least %15 or so...
Here is a pic of the set working, (if anyone is from the Toronto area you would
recognize this channel, it's the local CP24 station),
The weather on the top right should actually be 5 days, and the top right should display the current temp as well
so the temp and one of the days are fully off of the screen,
You can also see that the text in the report on the bottom left is cut as well.

Zeno,
The STR regulator is an STR380, so would that be an 80V regulator?
I've measured 123V, 124V and 148.5V on each of it's connections
(I couldn't find the regulator's diagram to tell which pin is which,
but looking at the circuit I believe I understand the input & output).
So far it looks like the output from the regulator is the 123V, going to a sand block resistor after which I get the 116V reading,
the line then departs from the PS board and going to the horiz. board on the right of the chassis.

>QUAD<
01-18-2016, 07:20 PM
Well, just looked up the specs of the STR380, and the output should be 122.8 so the one in my set is spot on...
I will take out the horiz. board later on today and have a closer look at it and measure some components.

tom.j.fla
01-18-2016, 07:56 PM
Not knowing your location that type of overscan is normal for a digital set top box, just set the aspect ratio to 4:3 and your picture will be close to normal. Do not know if the folks to the north have made the switch, but understand that they have. I see that on every set I have on a set top box. All the best,Tom

rca2000
01-18-2016, 09:19 PM
I am NOT sure about your readings...AND I see one power resistor that does NOT look too good, next to that large power resistor. . I seem to recall a lot of sets using series-pass regulators, often had a low-value resistor off of the regulator output, that OPENED..and when it DID...that big resistor then carries all of the load...and the B+ is low and not steady.. If you raise your b rightness level...see if your B+ stays constant. if NOT..you are NOT regulating properly...

>QUAD<
01-18-2016, 10:10 PM
Tom, the set top box is an old, non HD box, it's output is 4:3, but thanks for the tip though,
I just double checked to make sure, and also connected a little portable DVD player and played a
non HD movie to check how it looks, the picture is stretched the same way.

Yea most channels have made the switch here, but you have to have an HD box to watch HD programming.

rca2000,
If you are talking about the sand resistor on the right in the PS pic (on the edge of the board next to the filter cap),
then yea I was suspecting it right away as well due to the discoloration, but it tests out just fine, within an ohm of the specified value.

The B+ changes by about 2 volts from when I turn the brightness all the way from one end to the other...

rca2000
01-18-2016, 10:38 PM
No...I am tallking about the SMALLER One..in FRONT of it..Looks like it says "R324" or such.. That looks like the resistor that would be in line with the reg. output.

>QUAD<
01-18-2016, 11:03 PM
Ah, that is the resistor I was talking about in the original post, it is connected across the filter capacitor.
In the pic it sits in this awkward position because I've temporarily added a 3k resistor in line with it as it's resistance changd from 19K to 16K.
(I will replace it with an appropriate resistor later on, I am not going to leave this "fix" in place as I know that the bad resistor might drift farther with time).

The resistor that is in line with the reg is mounted separately from the board (on the back of the aluminum plate), it's 130 Ohm and measures 133.3 (with the regulator in place).

dishdude
01-19-2016, 01:22 AM
That picture looks pretty damn good to me.

Kamakiri
01-19-2016, 07:58 AM
If you can pick up any of the Buffalo stations, I can hook up my DTV converter and see what it looks like on one of my sets. Dishdude is right, looks damn good to me too.

zeno
01-19-2016, 10:00 AM
Must be a metal cased STR. Just as well, they are much better.
148 is the raw input ( collector)
124 reference ( base )
123 regulated out ( emitter) Note the 1 V apx diff, the
drop on the B-E junction.
Do the brightness test, 123V should stay steady & pix not change size.

BTW 19 K is a real odd value. Probably the heat changed
the color bands & it is a 15K. If that is in the B+ there may be a
'lytic after it opening, that will over heat it.

73 Zeno:smoke:

I'd understand if that would have been a bit of overscan, but the picture here is stretched by at least %15 or so...
Here is a pic of the set working, (if anyone is from the Toronto area you would
recognize this channel, it's the local CP24 station),
The weather on the top right should actually be 5 days, and the top right should display the current temp as well
so the temp and one of the days are fully off of the screen,
You can also see that the text in the report on the bottom left is cut as well.

Zeno,
The STR regulator is an STR380, so would that be an 80V regulator?
I've measured 123V, 124V and 148.5V on each of it's connections
(I couldn't find the regulator's diagram to tell which pin is which,
but looking at the circuit I believe I understand the input & output).
So far it looks like the output from the regulator is the 123V, going to a sand block resistor after which I get the 116V reading,
the line then departs from the PS board and going to the horiz. board on the right of the chassis.

>QUAD<
01-19-2016, 07:16 PM
Kamakiri,
unfortunately I do not have a DTV converter handy, so I can't try any of the Buffalo stations...
I've added a reference shot on how the same channel is looking on a 4:3 Sony video monitor I use for testing,
the signal is coming from the same box though using the RCA outputs.


So, I've looked at the horizontal board, and everything there looks peachy...
Replaced one small electrolytic that was showing 3.2uF instead of 4.7 but I doubt that will affect anything.
Also replaced the main PS filter cap that was showing 430uF instead of 470 with one I had on a board in my salvage boards box,
it was the same diameter as the old one so I thought why not, couldn't hurt (the replacement was measuring perfectly at 471uF).

I'm also adding a few clearer pics of the PS board, including the back of the plate it sits on that also holds the regulator and the 130 Ohm
sand resistor that sits in line with it, as well as a closeup of the R3249 resistor that supposedly drifted...
Well yea the value is odd, but the color bars look fine to me, so idk, the resistor doesn't look overheated.
All electrolytic in the PS and Horizontal board test just fine... (I use a capacitor tester).


Zeno,
I've done the brightness test as I mentioned above, and the B+ changes by about 2 volts, the picture changes in size for a split second
when I turn the the brightness all the way up but right away corrects itself properly, so I assume the 2V drift is not very significant,
correct me if I'm wrong though.


Inspecting the PS up close, I can notice that the STR has been removed and perhaps replaced in the past, as well as the resistor
in line with it (thermal paste smears and fingerprints around the STR, and soldering that doesn't look factory on the resistor...)
I am suspecting that the replacements might not have been the exact parts?

Another thought I have in mind is replacing the STR380 with an STR370 that I have here on hand, that should lower the B+
to 110V instead of 123V where it sits right now (the STR370 reference design diagram also shows that one 10KOhm
resistor should be changed for 12Kohm and the in line resistor should be 220Ohm so I can change those accordingly),
So let's suppose I'll do that, could I hurt things by doing this experiment?

If anyone has access to the schematics of this chassis or maybe even this set specifically, that would be very useful as I could then
know what the real values of the components are and what the B+ has to be.

Anyway I do appreciate the help and advises so far, and sorry for the lengthy posts!
(just trying to cram as much info as possible, heh).

Gunslinger
01-19-2016, 08:09 PM
I should have the microfische of that set. i will try to look tomorrow.

>QUAD<
01-20-2016, 01:06 AM
Thanks in advance Gunslinger, that would be very helpful!