Beige 4A - black screen and buzzing, despite new parts

[swissarmytin]

Hi guys, I'm having a teensy tiny bit of trouble troubleshooting a (normal, non-QI) beige 4A. I recently picked it up at a local vintage computer meetup as kind of a half-way project. The previous owner had it diagnosed and sourced all the replacement parts needed (new roms, 6114 memory, and sockets for all), but never got around to working on the board. 

 

I've since completed the work, but alas, she's still dead. At first, it did nothing but put out a black screen, so I went back, reflowed all my solder work, and reflowed some of the more suspect joints on various connectors, cartridge port, and on the power supply board. At the same time, I unsocketed the VDP, cleaned the schmoo that seeped over the sides, gave the pins and socket a good scrub, then re-installed it. 

 

I should also mention, one of the supplied replacement 6114 chips was actually a 6164, however I performed the mod from this thread:

 

After powering it on again, it still displays nothing but a black screen, but now there's a continuous low-droning beeping noise. 

 

Unfortunately, the 99 is far and away my expertise. I've never had to work on one as my silver 4A has been a solid performer, and to be really honest, I've never been particularly good at this particular kind of repair work, so I'm stumped on where to go from here. Any help bringing this back to life would be greatly appreciated. 

 

Thanks!

[+arcadeshopper]

Check the CPU..

If you look at the original roms I'd bet they are fine..



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[HOME AUTOMATION]

@swissarmytin

Say! You're kinda cute, for around here...
...did I just say that...
I'm sorry! Am I being gauche?

[WhataKowinkydink]

I seem to recall someone saying that every original VDP they'd pulled from its socket never worked after re-seating.

[swissarmytin]

3 hours ago, arcadeshopper said:

Check the CPU..

If you look at the original roms I'd bet they are fine..



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Alright, how do I go about testing it? 

13 minutes ago, WhataKowinkydink said:

I seem to recall someone saying that every original VDP they'd pulled from its socket never worked after re-seating.

Ouch, hopefully it's the socket that goes kaput, not the VDP...

[WhataKowinkydink]

59 minutes ago, swissarmytin said:

Ouch, hopefully it's the socket that goes kaput, not the VDP...

It sounded like the VDP itself.  Sorry I can't provide more information - I even went as far as looking through my history to see if any topic stood out to me.  I will make a mental note of it though and if I come across it again I'll mention it here.  In the meantime I seem to remember it was @Schmitzi who'd mentioned it.  Perhaps he can chime in with more.

[+arcadeshopper]

It sounded like the VDP itself.  Sorry I can't provide more information - I even went as far as looking through my history to see if any topic stood out to me.  I will make a mental note of it though and if I come across it again I'll mention it here.  In the meantime I seem to remember it was [mention=41141]Schmitzi[/mention] who'd mentioned it.  Perhaps he can chime in with more.

The first thing the computer does when it boots up is it turns off the sound chip if you're getting a loud noise it hasn't turned off the sound chip. It hasn't even looked at the VDP yet

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[GDMike]

I pulled vdp to exchange for F18A, that vdp never worked again..I dunno why

[WhataKowinkydink]

3 hours ago, GDMike said:

I pulled vdp to exchange for F18A, that vdp never worked again..I dunno why

Maybe it was you who'd said it - I distinctly recall someone saying as much recently as it stuck out in my mind as being strange and anomalous

[GDMike]

I pulled another out of a working computer as well, and I stuck that one in the machine that failed and it gave me a flashing black screen...I was pissed, I mean, I'm going to replace all 3 of my machines with F18A anyway, but I have no idea why the vdp quit on me. I know how to handle these, as far as protection, but this didn't make sense.

The machines all worked prior...  I dunno, but I do know that I put that F18A in all 3 and it always works..so??

 

[WhataKowinkydink]

1 hour ago, GDMike said:

I dunno, but I do know that I put that F18A in all 3 and it always works..so??

Hehehe  - well that's good at least

 

12 hours ago, arcadeshopper said:

The first thing the computer does when it boots up is it turns off the sound chip if you're getting a loud noise it hasn't turned off the sound chip. It hasn't even looked at the VDP yet

There is the patented startup beep: I assume then that the sound chip is turned back on only after the VDP is initialized?  The would seem to suggest as you say that it isn't the VDP. 

[GDMike]

I have a supposedly good 9901 that I picked up that I figured I might need to keep one handy, but as soon as I get money for another F18A, I'll be trying to get the other machines up.

 

[GDMike]

48 minutes ago, WhataKowinkydink said:

Hehehe  - well that's good at least

 

There is the patented startup beep: I assume then that the sound chip is turned back on only after the VDP is initialized?  The would seem to suggest as you say that it isn't the VDP. 

Regarding the beep, I can't remember if it beeped then went off or not..I was just seeing the flickering black screen at the time and COL, cussing out Loud at the time and maybe the beep was drowned out 

[swissarmytin]

Strange about the VDP...is it the socket that goes bad when unseating the chip, or is the VDP just that fragile? Never seen any other chip that dies like that from simply removing it...

 

Another point, though: the computer didn't work before I removed the VDP, so unless the previous owner also popped it out, there's yet another fault lurking somewhere in the system.

[GDMike]

I pulled one 9918 out last year because the color quality was weak, and I popped in another that I bought on eBay, and the colors improved but the chip died after about 15 mins.

Soni put the old one back in and it gave me the original poor color again, so that machine survived a pull. But the other machines, 3 others, didn't at all. And I replaced two with F18A boards and I think I sold that one or I gave it away, can't remember... but I suppose it's still beating, and the other I'm using as we speak. And I've got 3 or 4 ea 9918s in my parts bin, because, well I keep bad stuff too it appears.

[+acadiel]

I've de-socketed and re-socketed VDP's just fine without them dying, so dunno.

 

Is the "Buzz" the sound chip making a random noise over the audio channel?  If not, the system hasn't initialized, because that's one of the first things that's done.

 

SYSTEM POWER UP
POWER IS TURNED ON:

• 9900 CPU RESETS AND ADDRESSES LOW ROM LOCATIONS
• 9900 INITIALIZES
• 9900 SETS UP WORKSPACE REGISTERS IN 6810 RAM
• 9900 BEGINS READING FROM GROMS
• 9900 ENTERS TIME DELAY LOOP TO ALLOW STABILIZATION - SEC
• 9919 SOUND CHIP IS TURNED OFF
• 9918 VDP IS INITIALIZED
• 4116 RAM IS CLEARED - REQUIRES APPROXIMATELY 1 SEC
• FRONT PANEL DISPLAY IS WRITTEN INTO VDP
• 9919 SOUND CHIP EMITS BEEP
• 9900 CPU ENTERS KEYBOARD SCAN ROUTINE

Attacking the latest service manual that I scanned. Start the troubleshooting flowchart around page 87.

TI994A_HC_Servicing_Manual_Oct_1983.pdf

[GDMike]

I'll just drop another F18A in em, as they seemed ok once I did that on my two left over machines.. and I had to fix the broken keyboard ribbon cable, but yeah...thx for that wonderful troubleshooting guide.

[swissarmytin]

8 minutes ago, acadiel said:

I've de-socketed and re-socketed VDP's just fine without them dying, so dunno.

 

Is the "Buzz" the sound chip making a random noise over the audio channel?  If not, the system hasn't initialized, because that's one of the first things that's done.

 

SYSTEM POWER UP
POWER IS TURNED ON:

• 9900 CPU RESETS AND ADDRESSES LOW ROM LOCATIONS
• 9900 INITIALIZES
• 9900 SETS UP WORKSPACE REGISTERS IN 6810 RAM
• 9900 BEGINS READING FROM GROMS
• 9900 ENTERS TIME DELAY LOOP TO ALLOW STABILIZATION - SEC
• 9919 SOUND CHIP IS TURNED OFF
• 9918 VDP IS INITIALIZED
• 4116 RAM IS CLEARED - REQUIRES APPROXIMATELY 1 SEC
• FRONT PANEL DISPLAY IS WRITTEN INTO VDP
• 9919 SOUND CHIP EMITS BEEP
• 9900 CPU ENTERS KEYBOARD SCAN ROUTINE

Attacking the latest service manual that I scanned. Start the troubleshooting flowchart around page 87.

TI994A_HC_Servicing_Manual_Oct_1983.pdf 7.97 MB · 1 download

Alright, seems I definitely need to check the CPU is working first and foremost. What's the best way to go about testing it? Unfortunately, I don't have a scope, only a fairly basic Fluke meter

4 minutes ago, GDMike said:

I'll just drop another F18A in em, as they seemed ok once I did that on my two left over machines.. and I had to fix the broken keyboard ribbon cable, but yeah...thx for that wonderful troubleshooting guide.

Just out of curiosity, where can I get a F18A? Reading around, the mk2 isn't out yet, but I can't seem to find a place selling a normal F18A. 

[+arcadeshopper]

Just out of curiosity, where can I get a F18A? Reading around, the mk2 isn't out yet, but I can't seem to find a place selling a normal F18A. 

You need at least a logic probe

I've had a few F-18As in my store recently but they sold out. Also Hans has been making some in Europe



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[GDMike]

11 minutes ago, swissarmytin said:

Alright, seems I definitely need to check the CPU is working first and foremost. What's the best way to go about testing it? Unfortunately, I don't have a scope, only a fairly basic Fluke meter

Just out of curiosity, where can I get a F18A? Reading around, the mk2 isn't out yet, but I can't seem to find a place selling a normal F18A. 

Email Hans, he was on hold for parts last time I heard..

Hans Hübner <hans.huebner@gmail.com>

Edited April 13, 2022 by GDMike

[+acadiel]

Here's a really good YouTube Video to watch.  I've forwarded it to the section you need - and yeah, a logic probe would help.

 

He goes through testing the console ROM, but then finding out it was one SRAM that was faulty.  (The console ROMs are 2532 ICs - I think I have some of those if needed.  The SRAMs should be available on eBay, etc.)  Another possibility is the 4116 SRAMs.  But, he didn't have to troubleshoot those.

 

AtariAge is referenced (I saw @Schmitzi scroll by in the video)

 

 

 

 

 

[atrax27407]

FWIW, I can program console ROMs

[+acadiel]

53 minutes ago, atrax27407 said:

FWIW, I can program console ROMs

Me too... I'm local to the OP.

 

[+chue]

On 4/12/2022 at 7:00 PM, GDMike said:

I pulled vdp to exchange for F18A, that vdp never worked again..I dunno why

Silly question, but when you reinstall the vdp do you also install the heat sink (with new thermal paste)?

[GDMike]

On 4/13/2022 at 12:19 PM, GDMike said:

Pulling vdp

I did. Actually, probably wasted my heat sink compound, but of course I added it, put the board all back together and tested. With shield... and of course ended up breaking my keyboard connector during the process.

Edited April 15, 2022 by GDMike