I'm adding more information in the hope that someone can help me with the missing -15V rail. Three lines leading away from the power section, near TR21, are 00, DD, and II.

Tracing down II leads to the CPU outputting either 0V or 2.5V via the On/Off pin.

DD connects to the +5V supply and leads to an upper section that I have included below with readings. 00 also leads to this upper section, and I have included the readings as well.

From 00 is PP, which leads to the braking circuit. It feels like I'm getting close, as another problem right now is a constantly spinning platter.

From DD is NN, but that appears to lead to ground.

As always, any help is appreciated, thanks!

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If the platter spins in standby check 0TR1 (TIP32A).
I have seen more than one case of it being bad, not closing the 15V down but instead leaving it hovering around 5-6V.

And check copper traces in the -15V regulator area.
The traces are known to develop cracks near solder pads, that can be very difficult to spot. Particularly if your soldering iron is a bit too hot.

Martin

Hey Martin, I really appreciate the response.

Let me know if I'm misunderstanding your suggestion, but the 15V rail seems to work perfectly; it's only the -15V that is MIA.

Here is a copy of the circuit readings I previously provided. 0TR1 seems to be working fine.

As for a break, do you see anything odd within the circuit readings?

Hoping between these and the section included above, they hold a clue.

Thanks again!

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0TR1 provides a good 15V, yes.
But does it close completely in standby?

Martin

Thanks for clarifying, Dillen.

These readings were taken in the standby state.

Here is how the states change between standby on/off:

Standby: E:20V, B:14V, C:14V

On: E:20V, B:13V, C:13V

I should note, the platter spinning in standby is not a 'slow' spin, but quite fast.

Additionally, the Play/Stop buttons work intermittently.

If these measurements were taken on 0TR1, replace it!

Martin

Understood, replacing it. Thank you, Dillen! I will report back once the replacement part has arrived and been installed.

If you have a moment for me to learn, why this recommendation? In my beginner's eyes, it appears 0TR1 is working right, and the wrong voltage is being sent to the base during standby, meaning a different component is at fault. So why replace OTR1?

Thanks as always!

Hey, all! The swap of 01C1 was successful in moving forward the repair. Everything receives the correct power: 5V, 15V, and -15V. However, the unit doesn't want to start up properly. After experimenting, I found that the unit has a constant 5V at pin #39 (reset); I assume this should go low when switched on.

I can confirm that hitting the 'Play' button does reach the CPU. I dove into the reset circuit, but everything seems fine. All resistors test fine, the cap (C20) tests fine, the diode (D15) is OK, and so is the transistor (TR17). The base gets a constant 5V, while the emitter and collector are around 6V.

I'm a bit confused about this. I assume that the base shouldn't be 5V at all times, but where does the signal come from? The base only goes to D15, directly from around P2(2), which seems like it would always have a constant 5V. What am I missing?

Thanks!

Hey Dillen. Thanks, appreciated!

I'll have to research my understanding of transistors, as I thought TR17 looked good.

I thought that if the B was powered (5V), C and E should be open with the same voltage (6V).

I ordered a new bc557b transistor and it will be here tomorrow to swap out.

Thanks again.