Modern equivalent to 2SB605 transitor needed

[OmegaHyperio]

Been a while since i posted here,

well straight the point, im working on a Marantz PM350, and i have narrowed its fault down to the negative regulated power supply (probably, might still be the phono opamp). The negative rail is near dead (-1V with everything connected)

My thought is, its either the 2SB605 transistor, or the HZ16L diode (or possibly the cap across the diode).

Basically put, i need a replacement for this transistor. I have seen the KSC1008 mentioned somewhere as a suitable replacement, but i am not sure it will work, since its power dissipation is 200mW less then the 2SB605.

Any thoughts from you guys would be appreciated.

Also, for those wondering, i am measuring full negative rail voltage across R806, hence my thought, that something shorted to ground in that circuit, or is shorting it. I removed the EQ and power meter boards from the amp, with no effect. (so they seem good), the only part still connected is the phono opamp, and i doubt it has gone bad.

Feel free to correct my assumptions!

 

[petehall347]

BC640 should work .
p.s i cant find a 2SB605 transistor in the manual

 

[Hyperion]

Why don't you take ALL the load off the negative rail instead of just some of it? - the series pass transistor may be ok?

Let the regulator circuit sit 'free standing' - no load - then see what you get.

(I've never seen the circuit so I am assuming the 2SB605 is the series pass transistor?)

 

[petehall347]

think i figured it out ..
q808 ..but that is 2sb625 . diode is q801 .. cap is c810 ..
am i correct ?
if w712 is a plug pull it and check voltage again . at q909 emitter .

 

[OmegaHyperio]

think i figured it out ..
q808 ..but that is 2sb625 . diode is q801 .. cap is c810 ..
am i correct ?
if w712 is a plug pull it and check voltage again . at q909 emitter .

In the copy of the service manual i have for the amp, Q808 is listed as a 2SB605.

Hyperion Q808 is indeed the series pass transistor.

As to taking load of it, i have removed both W712 and W713, with no change to the missing voltage.


The only load i have not disconnected, is the RIAA preamp, as i have yet to find a easy method of disconnecting it (short of desoldering everything). But i might just give removing the opamp a shot, or trace the voltages, to see if i can find some bridges to disconnect it.

Disconnecting W712 and W713 is what led me to Q808

Thanks for the help sofar!

 

[petehall347]

this manual must be wrong the 625 is a t03 style .
the load should be off q808 after pulling w712 ..
so best test q808 and q809 .

 

[Tom B]

whatever you do, dont use the KSC1008, as that is an NPN transistor, and you need a PNP transistor.

Before you replace the transistor, measure the voltage drop across the B to E of the 2SB605 (Note that the manual says it is a 2SB625). If you measure anything above 0.7v, the transistor is open and needs to be replaced. It is common for regulators to open up B to E.
another way to verify if transistor is getting the right feeds, the collector should read ~31v, the base should read -17.8v, and the Emitter should read -17.2v. If you are missing the voltage on the collector, then R806 (270 ohm) has probably opened, or one of your fuses has opened.
If you read less than 0.7v across B to E, then you need to power off, remove power cord, and do some resistance checks.
Check the transistor (2SB605) for opens and shorts.
Check the zener diode (KZ16L) for short or leaky. You may need to lift one leg to check for leaky.
Check the resistance of the E of 2SB605 to chassis ground. If you are reading low resistance to ground in both directions, then you have something loading it down. Compare the load of the emitter from this transistor to the load of the emitter of the NPN transistor (Q807). The resistance reading should be similar, only reversed + to -)
As others suggested, remove all connected load (plug W712), to see if the load holding you down has been removed, but in reality, if you have a short holding the -17v down, you will probably have resistor R806 open as well as the transistor Q808 open as well.

Replacing the PNP transistor (Q808) I would use a 2SB649AC, and replacing the NPN transistor (Q807) I would use a 2SD699AC.

 

[OmegaHyperio]

this manual must be wrong the 625 is a t03 style .
the load should be off q808 after pulling w712 ..
so best test q808 and q809 .

It quite fascinating, i seem to have found an inconsistency in the HifiEngine copy of the manual, in the parts list, Q808 is labeled as a 2SD605, while on the schematic, its a 2SD625LK.
Both a PNP transistors though...

Also, look at the schematic again, i would need to pull W713 as well (which i have) If you fallow the rail, it also goes up to Q401, the IRAA preamp, opamp. Since its on the main board, i can not easily pull it.

I will check the actual transistor in the amp tomorrow, both for its functionality, and part number.

 

[OmegaHyperio]

whatever you do, dont use the KSC1008, as that is an NPN transistor, and you need a PNP transistor.

Before you replace the transistor, measure the voltage drop across the B to E of the 2SB605 (Note that the manual says it is a 2SB625). If you measure anything above 0.7v, the transistor is open and needs to be replaced. It is common for regulators to open up B to E.
another way to verify if transistor is getting the right feeds, the collector should read ~31v, the base should read -17.8v, and the Emitter should read -17.2v. If you are missing the voltage on the collector, then R806 (270 ohm) has probably opened, or one of your fuses has opened.
If you read less than 0.7v across B to E, then you need to power off, remove power cord, and do some resistance checks.
Check the transistor (2SB605) for opens and shorts.
Check the zener diode (KZ16L) for short or leaky. You may need to lift one leg to check for leaky.
Check the resistance of the E of 2SB605 to chassis ground. If you are reading low resistance to ground in both directions, then you have something loading it down. Compare the load of the emitter from this transistor to the load of the emitter of the NPN transistor (Q807). The resistance reading should be similar, only reversed + to -)
As others suggested, remove all connected load (plug W712), to see if the load holding you down has been removed, but in reality, if you have a short holding the -17v down, you will probably have resistor R806 open as well as the transistor Q808 open as well.

Replacing the PNP transistor (Q808) I would use a 2SB649AC, and replacing the NPN transistor (Q807) I would use a 2SD699AC.

I have stated in the first post, that i have removed W712 and W713 (both running off that transistor btw) with no effect. I will do the measurements tomorrow, and see what happens. As to R806, i measured it, and last time it still had a resistance to it, though it was getting hot rather quickly. (shut the amp down, to prevent it from going open)

Also, thanks for catching th KSC1008 being npn, i completely forgot to check that, and went off the post i found it mentioned in... Stupid me

 

[OmegaHyperio]

I have just disconnected all load (other then a 150K resistor) from the negative regulator. its still at 1.1V output, with 1.2V input (if i recall). The voltage across the zener is also 1.1V. So, my conclusion is, that the zener diode must have failed, and not the transistor (though i will order a replacement, just in case my hunch is wrong). I will stick the transistor into my cheap transistor tester later, and see what the HFE is.

Also, if i red the datasheet for the HZ16L correctly, its a 16V zener. I think the Vishay BZX55B16-TR should work as a replacement for it.

 

[Tom B]

It quite fascinating, i seem to have found an inconsistency in the HifiEngine copy of the manual, in the parts list, Q808 is labeled as a 2SD605, while on the schematic, its a 2SD625LK.
Both a PNP transistors though...

Also, look at the schematic again, i would need to pull W713 as well (which i have) If you fallow the rail, it also goes up to Q401, the IRAA preamp, opamp. Since its on the main board, i can not easily pull it.

I will check the actual transistor in the amp tomorrow, both for its functionality, and part number.

Be real careful here. Transistor "Q808" is a PNP regulator that should produce ~minus 17vdc on the emitter side. Being a "PNP" transistor it is a 2SB605, or a 2SB625 transistor. As a heads up in Japanese transistor markings, 2SA, and 2SB are PNP transistors. 2SC, and 2SD transistors are NPN transistors. Accidently swapping a NPN for a PNP or vice versa will have very ugly results. Yes the readings you are getting seems to point to a shorted Zener diode, but they usually short after the regulator transistor shorts. So I would get a replacement 2SB regulator transistor as well as the Zener diode, which is a 16 volt zener. And make sure you are using a dim bulb tester when powering up the unit after parts replacement.
Good luck

 

[Tom B]

Your Vishay Zener choice is fine. Actually any 16v 500mw Zener will work.

 

[OmegaHyperio]

Be real careful here. Transistor "Q808" is a PNP regulator that should produce ~minus 17vdc on the emitter side. Being a "PNP" transistor it is a 2SB605, or a 2SB625 transistor. As a heads up in Japanese transistor markings, 2SA, and 2SB are PNP transistors. 2SC, and 2SD transistors are NPN transistors. Accidently swapping a NPN for a PNP or vice versa will have very ugly results. Yes the readings you are getting seems to point to a shorted Zener diode, but they usually short after the regulator transistor shorts. So I would get a replacement 2SB regulator transistor as well as the Zener diode, which is a 16 volt zener. And make sure you are using a dim bulb tester when powering up the unit after parts replacement.
Good luck

Yeah, the npn pnp mix up was down to me not checking things properly. (did not buy the npn transistors)

Also thanks for the guide on how to read transistor names!

Also, thank you for pointing out that a shorted zener can be caused by a shorted transistor. i will be ordering both the transistors and diodes, and hope the fault was not caused by short circuit, but old age or something... Ill replace the caps in that circuit together with the transistor and zener, and then test on a dimbulb. (and isolation transformer as well)

I will be ordering the components for the repairs and Recapping of the amp (the main filter caps are in less then ideal shape) in a few minuets so yeah...

The replacement for Q808 is a BC640.

 

[OmegaHyperio]

Also quick question here, in a prebuilt amp, how bad would it be to increase the Coupling cap value from 3.3µF to 4.7µF. I ask because i can not get 3.3µF Silmic II's, in the size i need, and my father, who owns the amp, and has tasked me with restoring it, dose not want me to change them to my typical MKS2 caps. So Electrolytics it is...

 

[Tom B]

Increasing from 3.3 to 4.7 is not a big deal, but why not stick with 3.3uf??
I used to get caps via ebay, but had too many inconsistancies. I now get mine from Mouser, and found them reasonable priced and excellent quality. I usually use Nichicon Fine Gold (FG) . Usually spot on with the capacitance, and very low ESR according to my peak atlas Capacitane/ESR meter. If I need a 3.3uf @25v and they don't have it, I will go for the 35V or 50V version of the 3.3uf.
But if you do go to a 4.7uf, and this is a coupling, or audio bypass cap, I would use the same value in both channels.

 

[OmegaHyperio]

Increasing from 3.3 to 4.7 is not a big deal, but why not stick with 3.3uf??
I used to get caps via ebay, but had too many inconsistancies. I now get mine from Mouser, and found them reasonable priced and excellent quality. I usually use Nichicon Fine Gold (FG) . Usually spot on with the capacitance, and very low ESR according to my peak atlas Capacitane/ESR meter. If I need a 3.3uf @25v and they don't have it, I will go for the 35V or 50V version of the 3.3uf.
But if you do go to a 4.7uf, and this is a coupling, or audio bypass cap, I would use the same value in both channels.

I get my stuff from mouser as well. Also the reason i tend to use Silmic II's in the audio path. I have not got a lot of experience with the Fine Gold's, so i cant comment on the sound. Also, the only Slimic II i can get from mouser at 3.3µF is physically to large to fit in parts of the amp, so i need to use a smaller one, hence the 4.7µF 50V (3mm smaller).

Using the same values for both channels is a no brainier.

Also, i think ill get myself one of those Peak Atlas meters, it seems handy to have.

 

[Tom B]

I like using the peak atlas to test and match the new caps going in, as well as looking at the ones being removed. I have no connection to peak atlas, and actually feel it is a little pricy for its ESR and Cap testing feature compared to some of those kit versions on ebay, but I like the ability to test in-circuit for most caps, and the voltage bleed down function that prevents meltdown of the tester in the peak atlas.

 

[OmegaHyperio]

Just wanted to inform you guys, that the repair / restoration of the PM350 was a complete Success. Interestingly, the only part that actually failed, was the Zener Diode. R806 and Q808 survived.