black screen

[black screen]

I've obtained an oscilloscope and have no idea how to use it.  Could this somehow aid in discovering what is wrong with my TI-99/4a?

[black screen]

Alright, I finally received the MCM6810Ps, the sockets and the requisite kid-free time to desolder.  Nothing.  What a bummer.  What's the next step? I'm surely near the giving-up stage now. 

 

Thanks!

[black screen]

On 9/15/2019 at 5:45 PM, AwkwardPotato said:

Black screen w/ constant noise is a pretty common TI failure mode. First thing to try is pulling GROMs CD2156 and CD2157 and seeing if that changes anything. If there's no change, the fault most likely lies in one of the ROMs/SRAMs (the four wide chips right next to the CPU).

 

Unfortunately neither the ROMs nor SRAMs are socketed, and there really isn't a good way to narrow down the problem without a logic analyzer or oscilloscope. Replacements for the SRAMs are easy to find on eBay, but ROMs would either need to be programmed yourself or harvested from another board.

 

Ok I pulled the GROMs.  No change

 

I haven't been hugely successful at desoldering in the past.  Especially when the board is the thing I'd like to salvage (as opposed to the component itself).  Also, are the SRAMs the 4164s, 4116s  or the MCM6810Ps ?

 

Thanks!

[black screen]

nope no speech synthesizer. 

[black screen]

ok so I was able to get it hooked up to my TV. I've got the same black screen and a loud incessant noise/tone.  

[black screen]

Unfortunately, I don't have access to any other displays. I am using this av2hdmi upscaler device to display the signal on my hdmi computer monitor.   

 

Sound is another issue.  The upscaler device combines the audio (RCA red/white) with the HDMI signal, but the display doesn't have speakers.  I'm thinking I'll have to hack a pair of headphones and see if I can listen in that way. I'll report back on what if any sounds the 99/4a is making.

[black screen]

Hi All,

 

I recently obtained a 99/4a. After purchasing a power supply and video cable (thanks arcade shopper) I attempted to boot the device. The HDMI monitor detects a signal, but the screen is completely black (there are perhaps some evenly spaced but very faint vertical bars?).  fwiw the video cable does work with my C64.  the output voltages on the internal PSU appear to be correct

 

based on what I read here on atariage, I purchased a replacement 9918 on ebay. this did not solve the issue.  based on another post, I then removed the sound chip (SN94624) and tried both 9918s. this did not help. my next attempt was going to be to replace the ROM CD2156NL based solely on a blog post (at nightfallcrew.com).  

 

does this make sense as the next step? are there better ways to identify the source of the issue? thanks!

 

--jon