sl 1200 mk2 power problem

[woody007]

Hi

I am hoping someone knowledgeable with the SL 1200 MK2 series can help me out.

I have an sl 1200 MK2 with a problem I can't figure out. When this turntable got to me it was DOA, the lamp bulb was broken and shorted so I figure It suffered from the usual bad Q2, Q3, Q202, D301 and D3 so I ordered 3 D637 transistors and 2 5v zener diodes. after I replaced those parts the TT powered on but the platter speed was mostly unstable most of the time and badly fluttery at time, the LEDs/lamp also shuttered as the platter rapidly spun semi consistently (fluttering very quickly).

I thought maybe some of the components might be bad so I looked for cross reference components and switched transistors Q2, Q3 and Q1 (power regulator) with equivalent replacements. The result was more or less the same so I figured I should check the voltage at TP points (I went and bought a meter with voltage metering at this point). What I am getting is 30VAC at TP1/TP2 and 29.8V (DC) at TP5. I know I should be getting 20V at TP5 but I just cant figure out why I have almost 30V at TP5.

Any thoughts?

[Alec124c41]

Have you cleaned all switches and pots?

Cheers,
Alec

[woody007]

Alec, I have installed a new pitch control fader and look/measured at the other pot which are just fine as are all buttons and switches.

I really think the problem lies on the voltage side.

[Schrei]

Hi Woody,

As I told you, it seems to be something wrong at the power supply area.

Following the service manual try to trace the problem: Check Voltages at Q2 and Q3 terminals, measure resistance values for R2, R3, R4 and R5. I'm supposing that Q1 is OK, the value you measured for J2 at Q1 is too high!, I know that you haven't a capacimeter so if the turntable is 15 years old or over then change all electrolytic caps.

A scope will be necesary to test the ICs.

Does this link describes your problem (in this deck fails one AN6675)?

http://www.youtube.com/watch?v=DvI_OJ2xa9g

Regards,

Carlos

[woody007]

Carlos. Sorry for this very late reply. Work got extremely busy to the point of borderline pandemonium.

Anyhow, I had some time this morning to take some measurements. They are as follows.

R1: 5.5k ohms.
R2: 6.6k ohms.
R3: 2.67k ohms.
R4: 437 ohms
R5: 430 ohms.
Q2, B: 19.8vdc, C: 36.2vdc, E: 35.6vdc.
Q3, B: 19.8vdc, C: 19.8vdc, E: 3.2vdc.

As for the youtube vid, yes my SL 1200 is looking very much like the one on the video. It spins irregularly at intervals, faint clicking sounds can be heard and the LEDs/lamp flicker.

[woody007]

Well... long time no post on this particalar thread but this otta'be of interest to those of you who repair or tinker with SL 1200 mk2s so I'm posting my findings after I finally managed to repair this particular main board.

I initially believed my SL 1200's main board had a voltage problem at the voltage sector so I virtually change all the mayor components on the board's voltage part of the PCB. But no matter what, the voltage measurements were always bad.

I could never get the right voltage reading at key points on the PCB therefore I was a bit hesitant to change any ICs on the board and after a while I gave up and just installed a different PCB on the deck.

soooo.... Its been months since I first encounter this board and I was in need of a spare working PCB for a different project so I figured what the heck, and replace the most suspect IC on the board which is IC 101 part number AN6675. I should have done that all along, as a bad IC 101 is capable of causing abnormal voltage readings at the voltage regulators.

So there you have it. A bad IC 101 on an SL 1200 mk2+ can cause goofy voltages on the main board.