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TRS-80 M4 - Double Vision?

I'd have him hold the Break Key Down and Power Up to see if he can get to cassette basic.
If that works, have him type a line of "A" for 64 characters to see if that works.

It might be the just in 80 x 24 characters and not in 64 Character Mode.

Does that Model 4 have the Pot C210 to adjust for 80 Column Mode?
The original Model 4 PAL boards, through REV A, have two separate and
unsynchronized crystals, Y1 (20.2752 Mhz) and Y2 (12.672 Mhz). Y2 is
used only for the 80-column video timing. Y1 is used for the
64-column video timing and the Z-80 clock.

In the REV B and later PAL boards, there is only a single 20.2752 Mhz
crystal, which is in a 4-pin oscillator package labeled U206 (in the
same corner where Y1 was in REV A). The 12.672 Mhz signal is
generated by a phase-locked loop using an SE564 (U203) and several
passive components, including capacitor C210. In the REV B and C
schematics, C210 is shown as a fixed 33pF, and in REV D it was changed
to a variable capacitor, 6-50 pF. I have a REV B board with a
variable C210, so it seems the factories started using the variable
capacitors sometime before the schematics were updated to reflect this
improvement.
Click to expand...

Larry
 
ldkraemer said:
It might be the just in 80 x 24 characters and not in 64 Character Mode.
Click to expand...

That boot screen is TRS-DOS 1.3, Model III mode.

It does look like something is wrong with the horizontal hold/HSYNC signal, but alas I have no idea off the top of my head what could be acting up. Is it possible it could have developed a loose wire/bad solder joint in the harness between the monitor and motherboard?
 
Unlikely to be a 50/60 Hz issue - as I have a number of American import machines here that run fine.

I agree that this looks like a horizontal frequency issue.

It could be either the computer or the monitor - so the first thing (after checking the 80 / 64 character mode) would be to identify which of the two components (computer or monitor) is at fault.

The only practical way of doing this is to monitor the horizontal sync. signal frequency with an oscilloscope and comparing it to the specifications for the machine.

From a look at the start-up screen, some of the letters are corrupt. For example, the 'A' in TANDY is missing the horizontal line. This still may be a horizontal sync. issue (rather than a video signal issue) because the consecutive character lines may be all disjointed.

Unfortunately, as the machine is now on the other side of the pond, it all depends upon the diagnostic test capabilities (and willingness) of the purchaser...

Dave
 
So as other mentioned, the screen shown is TRSDOS 1.3 so it's in 64-character mode so fo the time behind the whole C210 and 80 columns is not on the horizon
I have requested the gentleman to open the case and look inside if the connections at the video board or end of the canon are possibly "dislodged partially"
waiting on that response now for a few days, as mentioned by Daver2, diags overseas can be difficult. but still trying to help the hobbyist get it running video wize properly as we obviously can see it booted from a floppy into OS.
more when I have it. and thank you for the pointers.
 
daver2 said:
From a look at the start-up screen, some of the letters are corrupt. For example, the 'A' in TANDY is missing the horizontal line. This still may be a horizontal sync. issue (rather than a video signal issue) because the consecutive character lines may be all disjointed.
Click to expand...
I don't think there's any problem in the character generation or the video-in signal (pin 8 in the video connector). If you consider the odd lines fat and the even lines lean, that "TANDY" is in the Jack-Sprat image that only contains the even lines. The A cross-bar is in line 3, and you can see it in the complementary Sprat's-wife image on the left side of the screen, which comprises only odd lines.

If he gets the case open without breaking the neck of the CRT, he can try adjusting the horizontal hold, labeled "L501" and "HORIZ HOLD" on the video board, in section D4 of the circuit trace. (I'm guessing from the white phosphor that this is an earlier Model 4, with this video board that is still essentially the same as in a Model III).
BookReaderImages.php
 
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>>> If you consider the odd lines fat and the even lines lean, that "TANDY" is in the Jack-Sprat image that only contains the even lines. The A cross-bar is in line 3, and you can see it in the complementary Sprat's-wife image on the left side of the screen, which comprises only odd lines.

That is what I meant by the text "This still may be a horizontal sync. issue (rather than a video signal issue) because the consecutive character lines may be all disjointed.".

If the plan is to adjust L501 - then a special plastic hex inductor adjustor tool will undoubtedly be required. The use of a screwdriver (or similar) will probably end with a cracked ferrite core...

Dave
 
The video analog board seems especially prone to shipping damage on M4s. A few years back I bought a nice NGA M4 from the US west coast. It was packed extremely well, but arrived with all four corners broken off the analog board. No CRT damage, fortunately. I was able to repair it with a bit of patience, bus wire and superglue.
 
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