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QRV09 Voltage

Started by Forte, November 23, 2014, 11:17:38 AM

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Having trouble with the voltage check, not getting the correct readings and have not been able to work out what is wrong, have never been good at troubleshooting.

Measuring from ground(using input ground for convenience, not sure if this is correct) to the large voltage regulator tab get the following results
IC1  5.08V
IC2  -20.95V
IC3  -20.9V
IC4  5.23V

Have checked the rectifier outputs and D1 is only 6.56V and D2 is -20.18V

Voltage reading on the input of the rectifiers is 8.5V AC for D1 and 18V AC for D2

Have removed the transformers from the board and both measure approx 21V AC, assume this is high as they are unloaded.

Any ideas on what the cause of these incorrect readings maybe?


Do you have a 12 V transformer?

If you check the schematics you can see where the tab of the regulators are connected. You are 100% sure that you have LM317 in location of IC1 and 3?

If you measure 1.25 V across R27, R33, R30 and R36, then the regulators are regulating.
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff


Yes the transformers are 12V Myrra 44159

Have double checked IC1 &IC3, both stamped N07A which should be correct according to data sheet

Have removed and resoldered D1 and the surrounding Caps and Resistor, not easy but after removing TR1 & C23 it was not too hard.  Now get 19V & -19V on  rectifier outputs.

IC4 now reads 12.65V
IC1 has dropped and now only reads 0.8V
No change to IC2 & 3, both still -20.9V

R30, R33 & R36 all measure 1.25V
R27 does not, only measuring in the mv range

Will have to get back to this in a few days, any more ideas appreciated.


Notice that the tab is on the output for LM317 and the input for LM337.

You see now where you have the problem.

Opamp soldered in the right direction? Caps, the right polarity?
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff


Missed the fact that the tabs were not the same for LM317 & LM337.

Input voltages and output voltages are correct for IC2, IC3 & IC4.

IC1 is still a problem.
Have checked the schematic and compared IC1 to IC4 since they should be the same.
Measure 19.5V at C23 and R25, IC4 input tab and C33 both measure 19.5V on the working regulator, but IC1 & C25 only see 0.5V?

Looking at my previous post IC1 & IC4 were both previously the same voltage, although incorrect. I have removed C23 since then and it was hard to get out, is it possible I have damaged the connection to the top layer or would this affect both IC1 & IC4?

Failing any other suggestions will try tomorrow to connect C23 direct to IC1 with a short wire.