Issue after replacing the zener 5V regulator

[dimkasta]

A while back, I replaced the 5V zener reference with a 317 regulator. It was working very nice with excellent sonic results.

Today I tried a new reg I am working on based on TPS7A4501

The problem is that the turntable seems to be in an accelerate-break-accelerate-break loop. I see no problem with the voltages.

Any idea what might be going on? The voltage is 5.08V

[NRG]

First thought: is the reg o/p oscillating? Do you have a 'scope? is it all ok with the 317 back in cct?

[Marco]

Is this more a topic for the DIY room, as I’m afraid you’re both talking gobbledygook to me!

For starters, which T/T is being referred to? Remember that not everyone here speaks ‘tech talk’!!

Marco.

[dimkasta]

Sorry for that. I posted in a hurry.

It is about a MK2.

It is not the reg after all. I messed up something and fed 31V to the TT. I have fixed the voltages now, but the TT is gone... I have no energy to troubleshoot it now and see what is fried... damn...

[Marco]

It is about a MK2.

A MK2 Techincs, I presume? Don’t let the sharing of too much information frighten you!



Marco.

[dimkasta]

Well on techiepedia forum I guessed it would be obvious

Anyway, yes SL1200 MK2

I m seriously bummed My preciouuuuuuus

[dimkasta]

This is the exact behavior

http://www.youtube.com/watch?v=t8mMACv10gY

I guess it's the AN6680... I will verify it tomorrow with my scope

[Light Dependant Resistor]

Hi
Marco ,might be best to move this thread to DIY section

Following the test procedures in the service manual, the area of interest is X201, IC 201, IC 301 and IC 302
I would check R211 a 10k resistor, and R215 a 4k7 resistor, and less likley the 50k trim VR201

You need to better identify where you are placing a LM317 but it looks like you are placing it where D2 was originally which needs
quite a bit of consideration, for instance if Vin of the 317 is the emitter of Q3 you would need to also maintain the relationship
of R2 R3 R4 and R5 , R2 and R3 are for instance a divider for the base of Q3

Given your present fault I would see if D2 a 5.1v zener, placing it back in observing cathode to the emitter clears and restores fault
If it does, then set about more carefully using a LM317 if needed at all. For LM317 vout is Vref ( 1.25 ) x R2/R1 +1 which needs
individual tailoring to that part of the circuit. There are better regulators than LM317, but it is a good part, but not necessarily in this
part of the circuit, where the zener is doing its function very well. A far better idea would be the use of two capacitors of 1uf
the first between the junction of R2 and R3 to gnd and then a second cap of 1uf between the junction of R4 and R5 to Gnd
each with suitable voltage rating.

Cheers / Chris

[dimkasta]

For the record, it was the two pitch control ics

[Cycleallday]

Hi
Marco ,might be best to move this thread to DIY section
Cheers / Chris

I prefer it here in the Technics section. I am trying to learn about this decks power supplies and other mods and its better to find them all in this one section rather than searching through general diy

Mel