Classic II weird issues after analogue board recap

[moothefish]

Hi, long time lurker here. I recently recapped my classic ii motherboard and analogue board as it stopped turning on entirely. Now I can get it to power on, but it behaves very strangely. 

The machine will power up, give a boot chime, then there will be a "tick" sound from the analogue board and the machine will reset, chime again, sometimes only half a chime, before resetting again. Sometimes it will chime, then immediately give the chimes of death, then reset again. And sometimes it won't even give a chime or will just go straight to the death chimes. I'm really not sure where to start with this one.

Given the tick sound, could this be a sign of a dead flyback maybe? I will admit I did the logic board recap a while ago and it was the first time ever doing smd cap replacement, and I did have to run wires in place of two pads (rest assured my skills have improved a great deal since then). So it could well be something I've done wrong. Any help is appreciated.

 

[LaPorta]

Did it work fine before the re cap? There could be another component that is not working properly. I destroyed an IC on a Classic by accidentally making a solder bridge between it and a cap I put in. Look for defects in your work.

 

[moothefish]

Did it work fine before the re cap? There could be another component that is not working properly. I destroyed an IC on a Classic by accidentally making a solder bridge between it and a cap I put in. Look for defects in your work.

No, it did some time back but eventually stopped powering on. Recapped the logic board and that made no difference, recapped the PSU and now have these symptoms

UPDATE: so I just tried powering it on again and now the machine boots as it should, single chime, I get display with a cursor and the insert disk icon (don't have a hard disk in it at the moment). However the display is veeery wobbly and shakes up and down, which isn't something it did before it stopped powering up.

 

[bibilit]

Probably still a problem with the AB. 

The display issues are a sign voltages are not stable. 

 

[moothefish]

Haven't checked voltages just yet, however at this point I suspect the issue may lie in the flyback or the circuitry that drives it. While the screen is shaking, the flyback buzzes a little and whenever it resets the flyback clicks and cuts out just before the reset. I've changed all the caps and one of the large black diodes in the power section so far. 

 

[jimjimx]

I agree with bibilit. Run a meter while running the machine.

And try to keep them next to each other, so you can keep an eye on both at the same time..

As far as what component(s) are  (might) be at fault.....  You’ll need more professional help than me.. Sorry.

I have my own Classic II problems that I don’t have time & money for.

edit:

So... Wait... What..

Why did you change one of the diodes?

Was it destroyed?

Are there bigger problems?

 

[moothefish]

I agree with bibilit. Run a meter while running the machine.

And try to keep them next to each other, so you can keep an eye on both at the same time..

As far as what component(s) are  (might) be at fault.....  You’ll need more professional help than me.. Sorry.

I have my own Classic II problems that I don’t have time & money for.

edit:

So... Wait... What..

Why did you change one of the diodes?

Was it destroyed?

Are there bigger problems?

I replaced one of them because while the diode tested ok, it seemed like cap goo had gotten into it and had eaten away at the outside of it, and had left a sticky black residue all over it. Rather than try and clean it I just replaced it with another one I had to hand. 

 

[superjer2000]

As noted, check the voltages. The initial rebooting could have been caused by over or under voltage. No reason to suspect the flyback at this stage.

 

[bibilit]

I will replace both usual two diodes next the Tda4605.

DP3 and DP4 IIRQ.

hard to detect but most of the times leaky, see my previous posts about AB boards. 

 

[moothefish]

Ok so I've had some more time to work on the classic. I have checked the voltages at the hard drive molex connector and everything seems stable there, 11.7 on the 12v rail and 4.7 on the 5v rail. Would these be low enough to cause issues? The voltages don't fluctuate at all when the machine resets itself. Anywhere else I should check voltages?

 

[maceffects]

This is really a strange condition, though I am certain it is related to the analog board.  I've never seen such a situation so I don't want to speculate as to what it might be on the board but I'm going to follow this thread so if there is a resolution I will know for future reference. 

 

[dochilli]

4.7 V is a little bit low. There is a potentiometer on the AB where you can adjust the voltages. But be carefull and check the voltages while you change the poti. And observe the voltages for a few minutes. 4.85 V up to 5V are good values.

 

[bibilit]

I agree with dochilli. 

4,85 volts is the minimum required to get it going. 

Don’t touch the potentiometer in the first place, increasing the voltage to crank the 5 volts line will increase at the same time the 12 volts line, and you will probably end with a voltage too high. 

The 5 volts line is important, not the 12 volts one, should work With 4,85 volts and 11,7 volts. 

 

[moothefish]

Thanks for the advice, I ended up adjusting the pot to see if that would help and the machine now seems to be booting consistently. Buuut the display is still very very unstable and the buzzing noise is still there.

I have another analog board on the way, so I think at this point I might pull the new caps off this board, put them on the replacement one and see if that one is a runner when it arrives. 

 

[superjer2000]

Do you have a video of the video instability?  Have you resoldered the 4 pin connector from the analog board to the display and ensured the pins aren’t burnt or oxydized?

 

[moothefish]

Do you have a video of the video instability?  Have you resoldered the 4 pin connector from the analog board to the display and ensured the pins aren’t burnt or oxydized?

I have reflowed the deflection coil connector solder joints and also checked the rest of the board over for solder joints, can't see any more at this point. I'll try and grab a video of it tomorrow

 

[bibilit]

As i advised before both diodes are responsible for instability. 

 

[moothefish]

Well, I've acquired a second analogue board for next to nothing, swapped caps over and have a similar result..(though the flyback isn't making unhappy noises anymore so yay?)  I'm thinking I've been rather stupid and one of my caps is the wrong value. Can anyone confirm the rating of cp11 ? It was missing entirely from the new board. I'm gonna kick myself so hard if that's what is causing this..

Also what value are those diodes? I don't have any to swap them out for 

 

[bibilit]

CP11 is 220 µf / 50 volt

Both diodes are 1N4148.