TS1000 error code 2 keeps happening

[bwinkel67]

Well, I swapped out the electrolytic caps and no change. Even on an LCD that doesn't get the jitter, the signal deteriorates (as does the LCD with the jitter). It seems as the RAM pack warms up (i.e. the RAM chips on the rear board) the video signal just degrades and gets wavy lines. That may be normal due to the power conversion from 9v but leaving the rear cover off of the RAM pack fixes all that...the RF video signal stays solid for a long time. So it's easy to solve as it doesn't require much heat to dissipate, you literally take the cover off and a less than a minute the picture is solid and the interference is gone. So in a room at mid-to-high 70's it gets steady-state pretty quickly.

I even tried mounting small heat sinks on each of the chips but it didn't change anything. The heat sinks warmed up, but as soon as it's enclosed in the back cover it heats up. I'm thinking of getting a tiny fan (penny sized) and mounting it on the inside and use the supplied 5v to see if that cools things down. There are two tiny vents that the air could be pushed through. Other option is to add vents to the rear of the case...maybe I'll practice mold-making on the rear case and design vents into it.

Would the simple composite upgrade below fix the video? Or will the interference persist? I know that when I just grabbed the video signal off of the ULA in doing an ad-hoc composite, it still saw interference but I may not have been getting it as clean as I could have.

BTW, does this composite fix add the backporch signal?

2016-01-03-zx81-composite-video-circuit.gif (2.13 KiB) Viewed 6936 times

[bwinkel67]

I think my last question was pointless...backporch relates only to RF, right? Composite doesn't worry about it, no? (Edit...no looks like backporch does apply to composite after all).

BTW, been running a simple scrolling "Hello" program now for 2+ hours and the RF video is steady and clear...this is with the back cover of the 16K RAM pack removed. So steady state is indeed reached. The room is about 77-78 degrees and the back of the board registers at 98-99 degrees.

Just bought another RAM pack for $10 on eBay (incl shipping) so I will see if it's my specific RAM pack or just the design. Unfortunately I couldn't get a high serial numbered one so I won't know if this is a dual board (like I have) or a single board until it comes in. If there's no difference I'll just turn around and sell it back on eBay (I had a $10 coupon that was expiring tomorrow so I should get most of what I paid for it back...no need hanging on to one I won't use).

[1024MAK]

If there is tearing, jitter or horizontal distortion of pixels on the RF output, it’s probably going to be the same with composite video.

The modulator just converts a 50Hz to 6MHz ‘baseband’ or composite video signal to a VHF or UHF signal by mixing it (or modulating it) on to a much higher frequency carrier wave. In the same way that with radio a 50Hz to 15kHz audio signal is modulated onto a RF carrier wave.

The main problems with the RF output are:

• At each stage of additional processing, the signal accumulates more noise and more distortion (so some in the modulator and some more in the TV’s demodulation circuitry),
• The frequency of the carrier wave from the modulator often drifts as the insides of the computer warm up, and some TVs won’t track the frequency drift.
• Because the modulator is using simple analogue circuitry, the output frequency is not exactly at the correct frequency as per the TV broadcast standards, some TVs therefore cannot tune to this frequency with any accuracy.
• You have to tune the TV in to the computers output.

The back porch is the name of a section of the video signal, if you have one of the first two ULA versions, they do not generate the back porch part of the video signal. Hence composite video will be affected, as will the RF.

See the relevant links in my signature below...

Mark

[bwinkel67]

Thank you Mark. Your answers are always very insightful and detailed. I will update this link when next I receive the new RAM pack (maybe by Friday). I am keeping my fingers crossed that I get lucky and get a single board version (later model). This one didn't have a serial number on the bottom and came from an estate sale. When I ordered the current TS1000 last year to replace a damaged one that I've had for 25+ years I lucked out and got one which gives a beautifully crisp RF signal (backporch and all) so maybe I'll be 2-for-2 :-/

If not I may actually try a penny sized fan to see if I can keep the air flowing inside when closed. I'm thinking with so little current draw it may work...we will see (I'll have a spare RAM pack after all). I've had my TS1000 with RAM pack now on for hours and the picture isn't budging. It has jail bars, which it gets at the start, but no wavy lines or other interference that starts up when the RAM pack gets warm with the cover. Just feels weird to run it with the back off and I fear something will short it eventually.