You are not logged in.

#1 2015-11-04 06:56:50

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

MacintoshTV Repair

The backstory:
After pining for a 5x0 machine, and a machine with a TV tuner (I've got 2 tuner modules and still can't get either working in a 630 or 6400), and seeing how much the 5x0's go for (with shipping!) on ebay, I decided to just get a non-working Macintosh TV.  Because I'm a sucker, apparently!
After getting the machine, I did the usual recapping of the logic board, and most of the analog board.  I ran out of 100uF 25V caps and will be reordering some more, but other than that pretty much all the caps were replaced.
Unfortunately, the machine still wouldn't power on.  Turning the switch on in the back, I could hear the analog board come on (screen degaussing?), but pressing the power button on the keyboard didn't do anything at all.
After tracing through a bunch of the startup circuit, focusing on the cuda and the little SOIC8 battery monitor chip, I determined all the traces of all the pins were in tact, at least one hop out from those chips.
Putting a Color Classic logic board in the machine made it boot up just fine, and putting the Macintosh TV logic board in the working Color Classic had the same non-booting results.  So it seemed limited to the logic board.
I noticed the startup circuit between the Macintosh TV and the Color Classic was almost identical, so started comparing, and still couldn't find any problems with the Macintosh TV's logic board.
I bought uniserver's CC schematic and traced out the whole circuit, and everything looked fine.  Making observations of the board while it's powered on inside the machine is a little difficult because of the case design.  Checking the ADB Power On pin, it had about 3.5V.  That seemed a little lower than expected, but the Color Classic's in this machine wasn't much higher.  I attached probes to the cuda where the ADB Power On pin attached so I could observe the voltage, and it was being grounded when the keyboard power button was pressed, so the cuda was being told to power on the machine.
The cuda has a signal to the logic board's edge connector that goes to the analog board to tell it to power on.  The pin is low when the machine is off, the cuda raises it, and then it is connected via a resistor to the 5V rail, which will keep the line high while it's on.  Then to power off, the cuda can ground it, turning the power supply off.  Attaching a probe to this line and observing it in system, it stayed around 0.9V and didn't move when pressing the power button.
Just to be sure the cuda was actually receiving power, I attached a probe to that and measured the 5V standby power, and it seemed good at around 4.6V.

At this point, the cuda had power.  It was being told to power the machine on.  It wasn't even attempting to power the machine on.
So that sounded like a bad cuda.

The Color Classic's cuda looked pin compatible with the Macintosh TV's, but I didn't really want to salvage parts from the Color Classic.  Instead, I noticed the 6200 had what seemed to be an identical cuda as well.  I certainly didn't feel bad about pilfering parts from a 6200, so I put its cuda onto the Macintosh TV's logic board.  No change.

At this point, I was about out of ideas.  I had been on irc talking to dougg3 through most of this, and he realized this would be the behavior if a cuda was stuck in reset, and asked if I had checked to make sure the cuda reset button wasn't stuck.  I checked it with the continuity test mode of my multimeter and it did not indicate a connection.  But, taking no chances, I removed the reset button entirely.  I certainly didn't need a cuda reset button for a machine that wouldn't even power on.  Boom, the machine booted!
Apparently there was enough leaked capacitor goo hiding under the cuda reset button to form enough of a connection to hold the cuda in reset.

General workings of the power on circuit:
There's really only a couple components in the power on circuit on these machines, consisting of the cuda (a 14pin IC), a battery monitor SOIC8, a cylindrical 2pin crystal for the cuda, and the battery.
The SOIC8 chip controls whether the battery should be providing power to the system.  Normally, when the machine is "off" or shutdown, but the power switch on the back is on, the power supply provides 5V standby power, and this powers the PRAM and the cuda.  The battery is only used when the power switch on the back is off, or the machine is unplugged.
The cuda is where all the startup logic happens.  It receives 5V standby power (or 3.6V battery power if 5V isn't available), and the ADB Power On pin is connected to it, with a pullup resistor connected to the 5VSB.  The cuda has another output pin that connects to the analog board's power supply.  This line is normally low when the machine is off, with a resistor to the 5V rail.  When the ADB Power On pin goes low, the cuda raises this signal to the power supply.  Once the power supply powers on, the 5V rail keeps it high until the cuda grounds it to shutdown the machine.

Neat learnings:
The power circuit is basically identical from the Color Classic through to at least the 6x00 machines, and parts can be interchanged without problem.  My Macintosh TV is currently running with a 6200's cuda.

Unfortunately, the story doesn't end there.  The monitor has some blotchy yellow coloration on the screen.  Like one of the colors isn't applying evenly to the screen, or a big magnet messed it up or something.

mactv1.jpg

The colors in the picture are pretty accurate with what I see.  The bottom left portion of the screen, and the top right both have a lot of yellow.
The Macintosh TV's analog board has identical tuning controls to the Color Classic's (described here, with diagram), and I've tried messing with the colors there, but they don't seem to affect the yellow blotchiness.

Any ideas from the CRT gurus?

Offline

#2 2015-11-04 07:05:20

mcdermd
Member
From: Corvallis, OR
Registered: 2014-05-12
Posts: 932
Website

Re: MacintoshTV Repair

I wish my MTV logic board(s) was that easy sad

I can't say on your MTV but in my arcade monitor experience, a degauss ring or some work with the purity adjustment rings would be in order.


Daily Drivers: 27" iMac 2.8 GHz Quad-Core i7 (Late 2009), 21.5" iMac 2.7GHz Quad-Core i5 (Late 2013), 11" Macbook Air 1.6 GHz i5 (Mid-2011)
See the restored heroes here.

Offline

#3 2015-11-04 08:06:58

macdrone
Member
From: Rainier, Or
Registered: 2014-05-25
Posts: 219

Re: MacintoshTV Repair

I need to find me a macintosh tv, cant believe I was able to get a TAM before the TV.

Offline

#4 2015-11-04 16:34:00

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: MacintoshTV Repair

Thanks!  Let's see, purity rings...  I assume this isn't some middle school thing.  smile  I'll figure it out, thanks for the pointer.  From reading, it does seem like that would be a good place to start.

Offline

#5 2015-11-04 17:19:38

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: MacintoshTV Repair

Boom, yup.  Looks like the fan came off during shipping and while it was rattling around, it knocked some rings out of alignment.  Thanks!

Offline

#6 2015-11-04 20:20:16

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: MacintoshTV Repair

As an addendum: CDROM drives need recapping too!

Offline

#7 2015-11-04 23:21:14

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 954
Website

Re: MacintoshTV Repair

big_smile


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

Offline

#8 2015-11-05 17:00:11

ClassicHasClass
Member
From: Electron Alley
Registered: 2014-05-26
Posts: 1,081
Website

Re: MacintoshTV Repair

Rinderpest?

What's your other machine named, Smallpox? Chikungunya?

Offline

#9 2015-11-05 20:53:11

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 954
Website

Re: MacintoshTV Repair

i had to google it… but things look good…:::     the last confirmed case of rinderpest was diagnosed in 2001


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

Offline

#10 2015-11-05 21:04:23

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: MacintoshTV Repair

Funny story!  Naming things usually needs a theme, like big cats, places in california, that kind of thing.  The logical progression for these is alphabetical.  Obviously, deadly diseases is a good theme for software.  And through a series of unfamiliar automation and some scripting goofs, that's how I ended up mailing the entire company about Anthrax.  Just weeks after the 2001 anthrax attacks.

Offline

#11 2015-11-06 17:31:37

ClassicHasClass
Member
From: Electron Alley
Registered: 2014-05-26
Posts: 1,081
Website

Re: MacintoshTV Repair

As someone who works in communicable diseases, that is incredibly awful and hilarious.

Offline

#12 2015-11-06 19:14:10

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 954
Website

Re: MacintoshTV Repair

hahah R O B!    good one!


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

Offline

#13 2015-11-06 22:47:36

mcdermd
Member
From: Corvallis, OR
Registered: 2014-05-12
Posts: 932
Website

Re: MacintoshTV Repair

bbraun wrote:

Boom, yup.  Looks like the fan came off during shipping and while it was rattling around, it knocked some rings out of alignment.  Thanks!

Magnets, man. How do they work?


Daily Drivers: 27" iMac 2.8 GHz Quad-Core i7 (Late 2009), 21.5" iMac 2.7GHz Quad-Core i5 (Late 2013), 11" Macbook Air 1.6 GHz i5 (Mid-2011)
See the restored heroes here.

Offline

#14 2015-11-17 23:21:14

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: MacintoshTV Repair

As an update to this story, the HDD died, and I wanted to replace it with a SCSI2SD.  Unfortunately, the molex power connector is upside down compared to a real hdd and the mactv has one of those adapters from the drive to a plug in edge connector that won't fit with the SCSI2SD's upside down connector.
I got one of those new V5 SCSI2SD's that are bus powered, but they still have the upside down molex connector.  So either I'd have to break the adapter, or desolder the molex connector.
I ended up choosing to desolder the connector.  The whole deal works fine that way!

I know, it's not the same presence without a whirring noisy hdd.  But I'm not a fan of spinny media anyway!  tongue

Offline

#15 2015-11-18 02:31:39

techknight
Member
Registered: 2014-05-22
Posts: 449

Re: MacintoshTV Repair

Maybe with a DSP and some wav files, we could "emulate" the noise from a little piezo squawker?

Offline

#16 2015-11-18 02:43:59

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: MacintoshTV Repair

Definitely needs to be a floppyemu feature!  The 1541Ultimate that emulates a C64 floppy drive has an audio out jack and emulates the floppy noises.

Offline

#17 2015-11-18 14:22:00

Schmoburger
Member
From: Australia
Registered: 2015-04-21
Posts: 281
Website

Re: MacintoshTV Repair

I want a TV so bad...


Stay hungry... Stay foolish.
G5 2.0DC, Yikes G4/500 Sonnet-Enhanced, B+W G3/450, 9600/200MP, 7600/200, iMacs DVSE Graphite and 600 Snow, 7220/200, WGS 7350/180, 6360/160, 5500/250 DE, Pismo, 2x Lombards, 6100/66DOS, 2x CC's, 3x Pluses, 512K, SE/30, SE Superdrive, 2x Classics, IIvx, IIci, IIsi, 3x LC520, 4x LC575, 5x P580, LC, LCIII, //gs LE, 2x ROM 02 //gs', IIe... and I'm outta characters!

Offline

#18 2016-09-04 20:06:31

joethezombie
Member
From: Idaho
Registered: 2015-08-20
Posts: 18

Re: MacintoshTV Repair

bbraun!  You are a HERO!  Thanks to your write up with the power-on circuitry, I was able to trace the problem with my MacTV (thanks again Falcon!) to that damn CUDA reset switch.  After removal, it came right up!  Woo-hoo!  I am unworthily living among GODS I say!

Funny thing about that switch, after removal I decided to test it, and maybe put it back in circuit after cleaning the board.  But it tests open all the time, even when pressing the button. Hmmm...


Apple: ][+, //c, IIgs, 128K, SE, SE/30, IIfx, IIsi, Q700, MacTV, 6100 DOS, 8100/110, G3 AiO, ANS700/200,G4 DP500
Commodore: 64, 128D, Amiga 3000

Offline

Board footer

About ThinkClassic

ThinkClassic specialises in the maintenance, repair, restoration and modification of Vintage Apple and Macintosh computers. Ask questions and find answers about classic Apple desktops, laptops, accessories and peripherals.