Marantz 4300 - Missing 10v in Power Supply

[CaseyWKC]

Hey all,
Finally got this Marantz 4300 on my bench that I'd been putting off for quite sometime.

Power cable cut, busted switch, blown left channel.

Anyhoo, I rebuilt/refreshed the right channel but before firing it up decided to check out the power supply.

It was swinging between 14-31volts and the trimmer didn't really have any effect.

Replaced H801 and 804 (the 2SD331's) and now voltage is stable but the highest I can get it is 25 and it should be at 35.

All voltages look normal except for the emitter of H801, it's that 24 volts. Resistors are all within spec as well, diodes test fine.

Following it to test points JM03 and JM04 - looking right past - HM01-HM04 are missing five or six volts as well.

I'm seeing around 7 volts on the base and collector of HM01 and only 14 volts on the emitter of HM02.
Then only 7 volts on the base and emitter of HM03, and and around 14 volts on the emitter of HM04.

Any suggestions would be much appreciated, I've been at it for hours now.

 

[CaseyWKC]

Installing a 10k trimmer in place of the 5k I can dial it in closer to 30, guessing if I toss in a 20k I'll get there, looks like I have a bad resistor somewhere.

Update : with a 20k trimmer installed I can get to 33.6v.

 

[ocdecio]

Check the zeners. Or you may have a short somewhere down the line, check power usage as well.

 

[CaseyWKC]

Check the zeners. Or you may have a short somewhere down the line, check power usage as well.

Both zeners were checked, one was damaged and reading as two diodes, has been replaced with a 6.8v zener.

What do you mean by check power usage?

 

[ocdecio]

Both zeners were checked, one was damaged and reading as two diodes, has been replaced with a 6.8v zener.

What do you mean by check power usage?

I use a watt meter to check if power consuption overall is above what I consider normal for the unit. For a 4300 say 60W.

 

[CaseyWKC]

I use a watt meter to check if power consuption overall is above what I consider normal for the unit. For a 4300 say 60W.

Gotcha, I’m on a 160 w DBT. Amp boards removed. No glow but I should pick up a wattmeter myself eventually.

 

[CaseyWKC]

Alright I am back for the weekend!

Check the zeners. Or you may have a short somewhere down the line, check power usage as well.

Cathode at H808 measures 6.74v anode 0.

Cathode at H809 measures 14v anode 0.

H805
E: 0v
C: 1.1v
B .01v

H806
E: .592v
C: .591v
B: 1.1v

H807
E: 0v
C: .589v
B: .592v

Off DBT so voltages aren't altered.

Thanks!

 

[rBuckner]

H805 isn't doing anything per the near same base and emitter voltages. Maybe they are shorted together?

 

[CaseyWKC]

H805 isn't doing anything per the near same base and emitter voltages. Maybe they are shorted together?

Checked and no luck there.

I got distracted finishing an SX 1250 but this guy is back on my bench now and will be my primary focus starting this evening.

Just need to figure this out.

 

[mbz]

Problem is H801e cannot be increased beyond +25Vdc, target is +35Vdc.
b/c/e voltages for H801,2,3 would be helpful.
Wanting H802 36.3V, H801b 35.7V

Looks like H803 is working too hard drawing too much current through R802,3.
Regarding zener H808, nominal 7.1V, you've gone with a 6.74V item which is a tad low, try to find a suitable replacement

I assume C805 (220.63V) has been replaced

 

[CaseyWKC]

Problem is H801e cannot be increased beyond +25Vdc, target is +35Vdc.
b/c/e voltages for H801,2,3 would be helpful.
Wanting H802 36.3V, H801b 35.7V

Looks like H803 is working too hard drawing too much current through R802,3.
Regarding zener H808, nominal 7.1V, you've gone with a 6.74V item which is a tad low, try to find a suitable replacement

I assume C805 (220.63V) has been replaced

Zener was replaced with a 7.2 or 7.4 volt Zener already. Somebody told me it was a tad high and I should use a 6.8 instead. No change regardless.

All caps replaced yes.

 

[mbz]

b/c/e voltages for H801,2,3 would be helpful.
Wanting H802 36.3V, H801b 35.7V

 

[CaseyWKC]

Sorry was in a rush this morning, with this incoming snowstorm I now have the whole weekend.

H801
B 42.6v
C 45.6v
E 24.3v

H802
B 25.53v
C 45.7v
E 25.02v

H803
B 23.02v
C 25.55v
E 6.74v

w/dbt.

 

[mbz]

Above measurements appear unreliable.
Expect H801b(42.6V) to be same as H802e(25.02V)
H801c=H802c and H802b=H803c are ok

H803b should be around 8V, being at 23.02V is near enough to the rails (H801e) voltage suggesting there is no current flow through R805.

Suggest measure resistance of R806(5k VR) between the 2 non-wiper legs, expect about 5k but more importantly not open, also measure R807(5.6k) in-circuit is fine, don't want to see open. If possible check for solder on these resistors. There should be about 1mA through R805 so about a 22V drop.

H801Vbe of 18V is probably a measurement error

H801 and H803 appear suspect from a Vbe point of view

Ditch the DBT if possible

 

[CaseyWKC]

Above measurements appear unreliable.
Expect H801b(42.6V) to be same as H802e(25.02V)
H801c=H802c and H802b=H803c are ok

H803b should be around 8V, being at 23.02V is near enough to the rails (H801e) voltage suggesting there is no current flow through R805.

Suggest measure resistance of R806(5k VR) between the 2 non-wiper legs, expect about 5k but more importantly not open, also measure R807(5.6k) in-circuit is fine, don't want to see open. If possible check for solder on these resistors. There should be about 1mA through R805 so about a 22V drop.

H801Vbe of 18V is probably a measurement error

H801 and H803 appear suspect from a Vbe point of view

Ditch the DBT if possible

H801 and H803 were already replaced - H801 with the 2SD313 and H803 with a new 2SC945

Two non wiper legs of r806 I see right around 5k as expected.

Ditching the DBT makes little difference with measurements but will do without from here on out. Just don't like probing the PSU board with it kind of "out" and the leads don't give me a ton of room to work with.

Across R805 I'm getting a .820v drop.
Solder joints are clean.

 

[mbz]

R807(5.6k) has to be open or bad solder joint, plz measure in circuit ok.
On a side note, did you replace C815(0.01uf)
Also try measuring resistance from H801e to chassis/GND

 

[CaseyWKC]

R807(5.6k) has to be open or bad solder joint, plz measure in circuit ok.
On a side note, did you replace C815(0.01uf)
Also try measuring resistance from H801e to chassis/GND

H801e to ground measures 2.6k ohms and climbs.

R807 measures 5.6k ohms and I've reflowed and board and checked continuity here.

I have not replaced C815. I will do that.

Cap changed, tested fine out of circuit, no change.

 

[mbz]

Across R805 I'm getting a .820v drop.

H801e to ground measures 2.6k ohms and climbs.

The 2.6k may be the problem, if you leave the probes connected a bit longer does it climb then stop at 32.6k?(R805,6,7)

Wanting to see about 1mA through the branch R805,6,7 that will give roughly 32.6V drop across the 3 R's ie, H801e(35V) to GND. There will be additional xxuA flowing through H803b from VR. Now because H801e sees a path to GND of only 2.6k, most of the current flows down that path and only a small part 0.82/22k =37uA goes through R805...

You've probably got a leaky cap to GND on that rail, need to trace trackwork for pins 5 and 7 of connector J801/J034

 

[CaseyWKC]

The 2.6k may be the problem, if you leave the probes connected a bit longer does it climb then stop at 32.6k?(R805,6,7)

Wanting to see about 1mA through the branch R805,6,7 that will give roughly 32.6V drop across the 3 R's ie, H801e(35V) to GND. There will be additional xxuA flowing through H803b from VR. Now because H801e sees a path to GND of only 2.6k, most of the current flows down that path and only a small part 0.82/22k =37uA goes through R805...

You've probably got a leaky cap to GND on that rail, need to trace trackwork for pins 5 and 7 of connector J801/J034

Staying hooked onto E of H801e to ground max it rises to is 3.2k ohms.

And when you say trace trackwork - am I looking at all of pins 5 and 7 on the PSU or tracing back?

Thanks for all of your help!

 

[mbz]

And when you say trace trackwork - am I looking at all of pins 5 and 7 on the PSU or tracing back?

As a first pass, trace the connections on the schematic, there will be (?) a local resevoir cap and noise bypass cap on that rail, these would be candidates.

Is the J801/J034 connector(?) unpluggable or is it wire wrap pins. Worth unplugging then dbt power up????