Author Topic: service manual and next steps to repair a sony ssm-20n1u crt monitor (Read 5376 times)

james_s · « **Reply #25 on:** January 25, 2019, 12:46:51 am »

I wouldn't expect replacing the electrolytic caps to solve a pincushion problem. In general I'm not a fan of the shotgun approach because it's easy to introduce new problems. Track down how the pincushion circuit works, often there will be a pin coming out of the main controller IC with a voltage that varies based on the setting in the menu. If you can find this pin, follow it and look for a dead transistor.

Many years ago I got a 14" SVGA monitor with a pincushion problem, the fault was a single bad small signal transistor.

oggie · « **Reply #26 on:** January 25, 2019, 01:18:42 am »

I figured out how to get into the service menu, thanks to someone on this video:

I only tried turning the 'pin amp' up and down from the original value to see if it would change at all, and of course it didn't.

I see in the circuit diagram q551, 2s02394-ef PIN OUT. It's fed from pin 5 (E/W OUT) of IC301, VDP3108 DECODER IC.

james_s · « **Reply #27 on:** January 25, 2019, 01:24:42 am »

Isn't there a pincushion adjustment in the user menu? It's rarely necessary to poke around in the service menu.

oggie · « **Reply #28 on:** January 25, 2019, 01:27:38 am »

Nope. There's almost nothing in the user menu on this monitor.

fzabkar · « **Reply #29 on:** January 26, 2019, 12:00:05 am »

Quote from: oggie on January 25, 2019, 01:18:42 am

I see in the circuit diagram q551, 2s02394-ef PIN OUT. It's fed from pin 5 (E/W OUT) of IC301, VDP3108 DECODER IC.

That's where I would start looking. The East/West correction output from the IC should be a "vertical parabola". Its frequency will be the vertical scan rate. Somewhere there will be an amplified version of this signal which modulates the horizontal output circuit, usually via inductive coupling.

oggie · « **Reply #30 on:** January 26, 2019, 01:04:54 am »

So I took a quick look at q551, and the numbers on it are of probably no use. It was hard to read, since the bar holding it to the heatsink wore the lettering down, but I think it said D2394 and e645. I can't find it in the service manual. But would it be a 2SD2394? They're not made any more, but what would be a good substitute?

fzabkar · « **Reply #31 on:** January 26, 2019, 02:25:36 am »

Does the transistor test bad? Is there a fusible resistor in its collector circuit? Which component(s) does it drive?

2SD2394, Rohm, NPN power transistor, Vcesat = 1.0V, 60V, 3A, hfe E=100-200, F=160-320, TO220-FN:
http://www.kontest.ru/datasheet/rohm/2sd2394.pdf

oggie · « **Reply #32 on:** January 26, 2019, 06:14:25 pm »

i've never tested a transistor in circuit, but my meter has a diode tester. It read .65v from b-c and from b-e while in cicruit. That means it's good, right?

james_s · « **Reply #33 on:** January 26, 2019, 06:41:33 pm »

It can be tricky to test conclusively in circuit but what you measured is certainly reasonable for a good transistor.

oggie · « **Reply #34 on:** January 26, 2019, 06:47:26 pm »

Well this is frustrating. I have this manual, but it's not a very good scan and is missing have the pages....

https://drive.google.com/file/d/1vmd90qea4q2fH-xCmfY9CWoe8GN2kbLy/view?usp=sharing

I could try to start testing the points mentioned in there with my scope. but I don't like testing live circuits when it comes to CRTs.

fzabkar · « **Reply #35 on:** January 26, 2019, 09:04:14 pm »

Which page of the manual has the E/W section of the circuit?

oggie · « **Reply #36 on:** January 27, 2019, 12:46:03 am »

page 27. although the poor scan has cut off part of the diagram.

fzabkar · « **Reply #37 on:** January 27, 2019, 12:56:54 am »

The transistor is being driven by one half of the dual op amp. This op amp gets its supply from a rectified tap on the secondary side of the flyback transformer. Check the fusible resistor between the rectifier diode and the tap.

oggie · « **Reply #38 on:** January 27, 2019, 01:09:16 am »

I assume you mean r511?

fzabkar · « **Reply #39 on:** January 27, 2019, 02:40:39 am »

I can't make out much from the blurry diagram. However, all you need to do is to follow the Vcc pin of the IC (pin #8) back to the transformer. There will be an electrolytic filter capacitor, a rectifier diode, and a fusible (aka flameproof) resistor in the path. The resistor typically has a value of 1.0 - 2.2 ohms. The diode should be a fast rectifier.

Edit: I managed to improve on the view. I now see that the op amp has a positive supply on pin #8 and a negative supply on pin #4. Each supply is generated by a separate tap on the flyback transformer. The components to check appear to be R510 and R511, D506 and D507 (RGP10G), and two 470uF, 25V capacitors.

Edit #2: I now see that the abovementioned supplies are shared by the vertical output IC (IC551), so they must both be OK. Instead I would examine the fusible resistor (?) between the collector of Q551 and inductor L551.

Direct download link to service manual:

https://drive.google.com/uc?export=download&id=1vmd90qea4q2fH-xCmfY9CWoe8GN2kbLy

oggie · « **Reply #40 on:** January 30, 2019, 01:22:57 am »

I checked, and the fusible resistors are fine. However, they appear to be just jumpers. Is that correct, or did they not bother using resistors?

fzabkar · « **Reply #41 on:** January 30, 2019, 01:40:32 am »

It looks like Sony took a cheap approach to the fusible resistors.

Another common problem is dry solder joints at the inductors, transformers, and the like. In fact many techs make it a practice to reflow the solder at all magnetics and power components such as ceramic resistors and power semis.

oggie · « **Reply #42 on:** January 30, 2019, 01:47:12 am »

Yea. I may have to do that just to see if that's the problem.

oggie · « **Reply #43 on:** February 02, 2019, 01:28:06 am »

So I went and reflowed a lot of the components, and still the same problem.

I sure wish I had a better service manual so that I could start testing it live with a scope.


EEVblog Main Site	EEVblog on Youtube	EEVblog on Twitter	EEVblog on Facebook	EEVblog on Odysee

Author Topic: service manual and next steps to repair a sony ssm-20n1u crt monitor (Read 5376 times)

Share me