Mac Classic video problem

[makkuss2000]

Hello to everyone, after recapped my Mac Classic (Analogic Board and Logic Board), everything was working really good but after 10 minutes i got an Horizontal line (picture1)
Before this thing happend, i heared a strange and little noise came from analogic board like a buzz but i didn't gave importance (i thought was normal) but after 10 minutes i got an Horizontal line (picture 1).
I started to chech what it could be and i found that on PIN 16 (power supply) of my TEA2037 i didn't have the 9.8V necessary to let start the vertical section.
I checked for a bad cap or transistor and i discovered tha the cap CF2 was gone (it's near the power of TEA2037).
After change it, the Vertical IC start to work but now i have this situation showed in the picture 2.
I checked everything (caps and resistor) and i controlled also the wave by oscilloscope on BD1 (YOKE PLUG) and i have this result:
PIN 1 : 22.5Khz wave (good)
PIN 2 : ground
PIN 3 : on this i don't have as showed in the sheet instruction the right frequency (i got 3/5 hz pulsing instead of 60.15 Hz stable) - picture 3
PIN 4 : 60.15 Hz wave (good)
I tried to change the TEA2037 but nothing, always the same result....
So i just ask for some HELP because i don't know what it could be.

 

[bpetersen]

Do you get a good 60Hz signal at HS1, the vsync signal from the logic board?

 

[makkuss2000]

Hello.. no signal at HS1

 

[makkuss2000]

However, i tested my logic board with anouther mac classic AB and it work perfectly.. so it’s a problem of this Analogical Board and i would like to repair it

 

[bpetersen]

It seems strange that you get a good 60Hz signal out of pin 8 but don't get a 60Hz signal in from the digital board at HS1.

I was reading this thread on VCF, though, that discusses debugging this area of the circuit and could be useful: https://forum.vcfed.org/index.php?t...ic-ii-vertical-collapse.1245014/#post-1342819

 

[makkuss2000]

Maybe my oscilloscope it has problem to show a 60hz wave (my model is mustool 8208) but 22khz is showed very well

 

[bpetersen]

But in your first message, you say you got a good 60Hz wave on pin 4. That is what I am confused about.

 

[makkuss2000]

Hello, sorry for delay, i just make same pictures from my osciloscope of my Analogic Board (with my Logical board connected that i tested that work perfectly).
These are signal that i got from the BD1 plug
starting from pin1 to pin 4.
As showed on pin1 i have 22.25Khz, nothing on pin 2 (ground) but nothing on pin 3 and pin 4 where i expected to see the 60.15 hz signals (with differet wave). I tested the TIA (on anouther Analogic Board) and it’s good..

 

[bpetersen]

Since your last post, I managed to get an oscilloscope to debug my problem (similar but on the horizontal). I at first had trouble getting the 60Hz traces too, but I realized I just wasn't triggering on them. Adjusting my scope, I got the one on pin 4 fine. The signal on pin 3 is the same height, so then I could get that too, but it was never stable -- the period varied enough that it was jumpy. At any rate, given that my vertical deflection seems ok, I'd say that's ok.

Here is what my pin 4 on the yoke looks like (attached). Granted, mine may not be ideal or correct either (would love feedback from others), but it looks roughly like the drawing in the schematic. I do worry that it isn't smooth though. My horizontal looks way worse (not smooth at all).

 

[makkuss2000]

Since your last post, I managed to get an oscilloscope to debug my problem (similar but on the horizontal). I at first had trouble getting the 60Hz traces too, but I realized I just wasn't triggering on them. Adjusting my scope, I got the one on pin 4 fine. The signal on pin 3 is the same height, so then I could get that too, but it was never stable -- the period varied enough that it was jumpy. At any rate, given that my vertical deflection seems ok, I'd say that's ok.

Here is what my pin 4 on the yoke looks like (attached). Granted, mine may not be ideal or correct either (would love feedback from others), but it looks roughly like the drawing in the schematic. I do worry that it isn't smooth though. My horizontal looks way worse (not smooth at all).

Hello, this is what i get from pin4 on a good Analogical board that i use the check the difference:
If i see yours is like mine

 

[makkuss2000]

Hello, this is what i get from pin4 on a good Analogical board that i use the check the difference:
If i see yours is like mine

On pin3 you should have this wave:

 

[bpetersen]

Could you please post a good wave of pin 1? That is where I think my problem is. Thank you!

 

[makkuss2000]

This is the wave on pin 1 of a working Analogic Board

 

[makkuss2000]

Hello to all, i tryed many approuch and controll on this board but what i suspect is that if i take a look on the wave and voltage (by oscilloscope) of a good Analogic board and on the wave and voltage of the AB that i’m tryng to repair, what i discovered is that there is a big difference of dimension (in voltage). In attached “figure 1” the pin 1 (Hsync) of good AB, show correctly 232 vp-p (it should be more or less 300 as indicated in the schematic) but in the “figure 2” from the bad AB on the pin 1 i have the same type of wave (and frequency) but the voltage is very low (148 vp-p) almost the half and in effect the results of this difference is that the image looks reduced of a half… i have the same problem for Vsync.. same wave and frequency but half or reduced voltage…

 

[makkuss2000]

Hello… finally..i Resolved! it was a bad LM317…it seems to work but the voltage, from one side was correctly 38v but to other side, only when i plugged the crt monitor (i worked to resolved this case without plug the crt monitir) strangely went down under 20v (and not 30 or more as needeed m)…and so everything went bad to high voltage side.

 

[bpetersen]

Congrats! I am surprised you had any picture at all. I had a bad LM317 and got nothing on the tube. Good to know.

 

[makkuss2000]

yes the bad LM317 went me far from solution because it worked without tube on…but it went bad (dropping voltage) when i connected the tube on board just to see if i saw something changed on the screen.. unbelievable! Thats mean that when you need to repair the analogic board.. everithing should be all togheter to see if something change..