Where to start diagnosting a discman which won't power up ?

I picked up a D-11 in working condition, it takes a long while to focus so I wanted to replace some of the caps 1) next to the 9V jack and 2)next to the PWM chip. After 1) the discman is still working, the focus problem remains so I went on to 2) yet the discman no longer powers up afterwards The screen no longer lights up, I measured the current and it draws around 30mA when it's plugged in.

I was using battery to test during the repair, I didn't disconnect the batteries because I thought only desoldering the battery cables would do the job. Maybe I fried something for hanging two charged cables on the board? All the solder joints of the capacitors I've changed have been tested for connectivity and they're nicely connected. I couldn't test the new capacitors for their capacity but I did test them with a multimeter and they do charge(as the resistance augmented). What should I test for now? I don't have much skills on this but I'm willing to learn!
Here are the schematics around the power section.
Appreciate your help!
Edit: grammar

 

Thank you for your reply!

I think I've seen that book! It it really helpful!

I've seen this video a couple times, it's cool to see someone not specialized in the domain to fix something too. However that's also my difficulty here. I'm willing to learn and to dive deeper into the circuit to test each component, learn about their purpose in the circuit and how to diagnose their condition. Where could I learn "identifying the problem in the circuit" ?
Thank you!

 

In my experience, whenever you do something like say change a capacitor or transistor, and it causes an undesired result, you need to 'undo' your repair, and return it to how you had it originally. If you take pictures of the board before/after as you repair things, you will know exactly how to 'undo' your changes.

With that said, you need to use the schematic and check voltages along the circuit path from the point of entry (9v jack) to the voltage regulator, to the other areas of the system. You will most likely find a area where you get voltage on one side of some component, but not the other. This is a really simple way to check all circuits for failed power components.

Start with Q451 and Q453. Verify all of the voltages pictured in the schematic are the same for those components. Also, check the capacitors around the regulator area to verify they are not polarity switched, or bad.

You really should buy a capacitance checker if you don't already have one.

 

Hey thank you for your help!
I marked all my questions in BOLD for readability

that's true, however I thought the original capacitors are basically dead, I threw them away before I had this thought... Will remember the next time !

Makes sense, however could you please give more guidance on this one ?
I have a few noob questions in detail, hope you don't mind their simplicity but I really can't wrap my head around these.

1. Take Q453 for example, how can I identify it's pins if I were to measure it? It's not listed on the manual
2. These arrows pointing towards branches with values, are they supposed to be voltage measurements?
3. In the case of Q413&414, nothing is listed in the schematic. How should I measure them?
4. What should the grounded pin connect to? Can I ground it to anything to measure the voltage?

I don't understand this totally... Voltage is the difference of electrostatic potential(according to me and wikipedia), how would "one side has voltage and the other doesn't" show up? I mean voltage is the difference between two values, one side can not have voltage since there nothing to compare to, there wouldn't be any difference in value?(I believe this is the same as question 4)

Done that before but will make sure again!

Thank you !

 

Totally fine, that happens!

Yes, the arrows pointing to the pins on the regulators are voltage values.

They are clearly listed in the manual. There are 3 pins. Emitter, collector, and base... these are the three principle pins of a transistor. In this case, it appears SONY is using a couple of transistors in series to make a voltage regulator... Here's a helpful image for you:



Collector and emitter are on one side of the transistor, the side with two pins, and the base is on the other. So, when you are looking at say Q451 on your board, the side with one pin is the base, and the other two are the collector and emitter. You can measure those two by just guessing. If I'm reading the schematic right, you should be getting 8.7v on the collector, 7.3v on the base, and 6.7v on the emitter. The emitter always has the arrow pointing out in a NPN configuration.

Remember, you can identify NPN transistors as the emitter arrow pointing out, and PNP as the arrow pointing in. Don't worry too much about the logic, just know how to identify them on the schematic.

It is not always beneficial to measure a transistor, because they are not always used as regulators, sometimes they are used as switches, op-amps, etc. That is why SONY doesn't include the values for those. The only reason we are taking a look at say Q453 is because it looks like Sony specifically says they are regulators in the service manual:

Any transistor that has voltage values pointing to it, should be measured, if you care about diagnosing that area of the circuit. You can also measure diodes and resistors, that can come in handy.

You can connect the red lead on your meter to the E,C, or B pin on the transistor, and find a safe board ground for your black lead.

So, it’s a voltage regulator, we need to make sure it’s working correctly, not shorted or burned up. The way to do it is check voltage. Pretty simple, right?

 

Whoa thank you so much! that's so much clearer!

Dumb question here, where's a board ground? For D-15 because the optical block's shield is grounded I connected the black pin to it. Could I do the same in this case ?

Thank you !

 

No, that’s not a dumb question! Sometimes, it can be very difficult to identify true ground points vs just metal!

If the laser is plugged into the board and secured to the chassis, then I say try it. It’s probably fine. I assume your talking about the metal underneath the laser?

Also, the metal bit around the cd block has a wire connecting it to the board on some models, that is a true ground I think.

 

Ah now I know! I'll try to measure with this in mind!
Edit

Yep that's what I was talking about!

Thank you !

Update on the measurements:
Neither of Q453, Q451 give out a correct voltage on the manual. I got less than half of the values written on the manual of all the pins of these two...

 

Try measuring the voltage while attempting to turn the unit on. Double check that the unit's lid close switch is working.

Let's specifically focus on Q451. Check for for 8.7v volts on the collector. also check for about 9v on the positive side of C403 and on one side of C401. It's so close to the power plug, you shouldn't be getting half of the values.

Also, verify the presence of PS401. If you have a UK model, it's present.

 

Yes, all cables should be connected if possible. Remember, you want to simulate the conditions of the unit working properly as intended.

 

Got it! I'll try with this in mind.