Recent content by jonschultz

That's a good sign because it means the AC section and the CRT supply section are working. The logic board supply side could still have a problem. Which TDA4605 did you have discharge on? There are two, one for each of the switching supply transformers. In any case, I think the CRT side (which...

Are you now getting no voltage on RV26 and RF19?

When a CC seems to be this dead, I recommend checking some of the low-voltage supplies. Many of them will normally be running even without booting (shouldn't even require an installed logic board), you simply have to have the hard power switch on. You can check the 8.3V and 24V supplies first...

Over the years, there have been lots of discussions surrounding the infamous DL21 and DL22 18V Zener diodes on the Color Classic analog board and the damage they tend to induce over time from their high power dissipation. There's scorched PCBs, reduced life of nearby CF8, generally undesirable...

Well CP35 appears to be in the power supply section. I'm less familiar with this territory of the analog board, but I think CP35 might be a decoupling cap for the switching power supply IC nearby. If something went wrong there, then the almost nothing is going to get power. Time to start probing...

Yeah, the bulging is bad and a fairly typical problem on Color Classic analog boards, precisely because of the heat generated by those two nearby diodes. This cap is also part of the vertical section and could definitely be a source of your display problems. The diodes in question (DL21, DL22)...

Yeah I agree, the DF2 voltage is suspiciously high. Do you have the correct value for RF11, which biases DF2? I think it should be 370 Ohms.

Excellent suggestions regarding the voltages to check. I was also going to mention that checking a flyback-generated voltage would be a good verification, as well. Most are pretty large, but one is reasonably low for safely measuring with a DMM. That's the one on pin 11 of the LM2418T (the...

I measure about 22.7V across CF10 on my system. Like a lot of components on the CC analog board, it's not very easy to probe from the top side, especially with the machine running. I soldered some probe wires on the underside of the board and fed them out the back to my multi-meter.

It's the 220uF 35V electrolytic, just south of the two large, blue, rectangular film capacitors near the top center of the image. Also FYI, the IC just to the right of CF10, clipped and heatsinked to the wall of the RF cage is the TDA8172. This is the vertical deflection IC.

I thought I would share some of my progress on getting VGA output on a Color Classic using my XC1186B reverse-engineered replacement board. It's looking pretty good, and requires just a little extra circuitry beyond my v4 design (which I have in breadboard form at the moment, hanging off the PCB...

This might simply be from the horizontal deflection (refresh) now running at 67Hz instead of 60Hz, and there just happens to me more resonance. The coils change shape ever so slightly and vibrate from the large deflection currents, and the vertical frequency is low enough to detect audibly. I’m...

Hi @surfer150, this is an easy fix. What you're seeing is that the G2 voltage (sort of like the black level control right at the tube) is too high and you're also starting to see "retrace lines". This is easily adjusted with the G2 potentiometer ("PL2 VG2"), on the left side of the analog board...

I see, but a bright, horizontal line means that vertical deflection has failed. Horizontal deflection is still working just fine in that case. Failure of horizontal deflection almost always results in absolutely nothing on the CRT functioning because a lot of the circuitry depends on the flyback...

I'm not too familiar with the TDA1170N, but it looks like it's a vertical deflection IC, similar to other ones that I've seen. I don't think any of the horizontal deflection functions are handled by this IC, so it wouldn't have any effect on the width of the raster (though, a caveat would be...