FAQ  •  Register   •  Gallery •  Login

It is currently Fri Aug 29, 2014 11:06 am

Offset problem with TFM-55?

<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Mon Nov 03, 2008 3:20 am

Re: Offset problem with TFM-55?

If you need FR603's I can send you some


That would be great Rich. I could pay you with Paypal I guess. I need 8 FR603's. Let me know.


Also do you have any transistors 2SC3467 and FDH400 diodes hanging around?

Not so easy to find without high domestic shipping costs in the UK.
Min order: 50 dollars, 100 units, business accounts only ](*,) ](*,)
........
My local cheap supplier cannot get hold of them (the one 1 block from my parents house). :(


8) 8) 8)
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

RichP714

SILVER-7t

Posts: 1814

Joined: Fri Oct 12, 2007 2:12 pm

Post Mon Nov 03, 2008 12:52 pm

Re: Offset problem with TFM-55?

brit01 wrote:
If you need FR603's I can send you some


That would be great Rich. I could pay you with Paypal I guess. I need 8 FR603's. Let me know.


Also do you have any transistors 2SC3467 and FDH400 diodes hanging around?

Not so easy to find without high domestic shipping costs in the UK.
Min order: 50 dollars, 100 units, business accounts only ](*,) ](*,)
........
My local cheap supplier cannot get hold of them (the one 1 block from my parents house). :(


8) 8) 8)

I have FR603's
I don't have FDH400's
For 2SA1370/2SC3467 transistors is use the 2SA1837/2SC4793 pair

the stock units are 200V, 100ma, 1W devices, and I the ones I use for my mod are 230V, 1a, 2W devices

The only thing to remember on these is that the pinout on the circuit board is ECB and these are BCE so you have tyo moount them backwards......let me know
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Tue Nov 04, 2008 4:39 pm

Re: Offset problem with TFM-55?

Hi guys,

I have a doubt about the ceramic caps on the RCA input board (and main for the matter of fact).

Why are these ceramics rated at 1000 V? I mean on the main board there are no voltages even close to this amount.

Maybe for some reason I'm not aware of.

#-o #-o #-o #-o
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

RichP714

SILVER-7t

Posts: 1814

Joined: Fri Oct 12, 2007 2:12 pm

Post Tue Nov 04, 2008 6:28 pm

Re: Offset problem with TFM-55?

I can't think of a reason either; most of the ones I found (I didn't look for all of the ceramics) were either in feedback loops or shunts to ground for high freq noise......maybe Carver got a deal on a zillion of them
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Wed Nov 05, 2008 3:22 am

Re: Offset problem with TFM-55?

maybe Carver got a deal on a zillion of them


Lol... I can see that happening.

I was shopping for some 1000V caps this week but had trouble finding them. Ended up buying some 2KV.

Then I was thinking (a bit slow I know) .. why the hell do I need 1000V??? I soldered in 4 x 2KV ceramics. I'll leave them in for now and use lower voltage ones for the remaining caps.

I could get away with some 50V-100V ceramics on the rca board. Min 100V I think for the main board.
I've almost finished replacing all small electros on the board also. Found a couple of really shady looking small caps. Looking quite bloated.


Those caps C513/C515 on the schematics are not on the board, neither can I find the location spot for them. Strange. Maybe another change in the design.

Have a look, the caps surrounding R209/211 on the schematics.

I wonder what effect these caps would have on these 62 ohm resistors.
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

RichP714

SILVER-7t

Posts: 1814

Joined: Fri Oct 12, 2007 2:12 pm

Post Wed Nov 05, 2008 12:22 pm

Re: Offset problem with TFM-55?

brit01 wrote:
maybe Carver got a deal on a zillion of them


Lol... I can see that happening.

I was shopping for some 1000V caps this week but had trouble finding them. Ended up buying some 2KV.

Then I was thinking (a bit slow I know) .. why the hell do I need 1000V??? I soldered in 4 x 2KV ceramics. I'll leave them in for now and use lower voltage ones for the remaining caps.

I could get away with some 50V-100V ceramics on the rca board. Min 100V I think for the main board.
I've almost finished replacing all small electros on the board also. Found a couple of really shady looking small caps. Looking quite bloated.


Those caps C513/C515 on the schematics are not on the board, neither can I find the location spot for them. Strange. Maybe another change in the design.

Have a look, the caps surrounding R209/211 on the schematics.

I wonder what effect these caps would have on these 62 ohm resistors.
It's probably safe to stay around 200V for the main board ceramics. 100V is probably fine, as you say.

I have no idea why C513/C515 would be there; sometimes the rail supplies have ceramics to ground for filtering high frequencies, but bypassing those resistors I have no idea why. I also have no idea why they are there in the schematic and not in reality. We don't have very comprehensive information on this late model Carver.
<<

BillD

User avatar

(pair of) SILVER-7 TUBE AMPs

Posts: 7295

Joined: Wed Jun 06, 2007 8:29 pm

Location: The west's most mid-western town, Scottsdale, Arizona

Post Wed Nov 05, 2008 1:03 pm

Re: Offset problem with TFM-55?

I would probably say they are there because they aren't in the power supply. I've been doing a little power supply research, and the output of big caps sometimes has high frequency content, either before or after being regulated. (flat line on a volt meter, but has hash in it. Those little 0.1µF or less ceramic (or poly) caps can filter that off before it is used to power op-amps.
It should sound like it isn't there!
There is a difference between hearing and listening...
Making life enjoyable through expensive electronics.
_________________
Carver: C-4000 & C-1 preamps, PSC-60 preamp/tuner, TX-11a tuner, M-400 (2), C-500, M-500, M-500t, M-500t Mk.II, A-500x, AL-III loudspeakers (2 pr.)
Sunfire:Theater Grand III processor, Ultimate Receiver, Cinema Grand Signature 400 ~ seven, True Subwoofer Mk. II, D-10 Subwoofer
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Thu Nov 06, 2008 2:06 pm

Re: Offset problem with TFM-55?

:( :(

Well now after changing most of the small and large caps we have a new problem ](*,) ](*,) ](*,)

The dc offset has been reduced from 32 to 20 which is great BUT the good side that was just 3-4 mV is now showing a NEGATIVE offset of about 4 mV. Bias both sides if fine at 2.5mV.

AND the rail voltage will only rise to 83 (E4)Volts Max! I have tried adjusting it from the V1 trimmer but it does not change the voltage which is the most worrying part. And E3(22V).

One of the big caps damaged maybe? (Now C505/c506/c509 were taken out and I put the old ones back in today because my mail package with the new caps is going to be another week) My impatience. I could have damaged one of the old caps taking them out. maybe a result of the rail voltage??


Caps C501/C502 are brand new.

btw I change the small caps on the power board C4/C5. :-k :-k :-k


It's still fighting me.

Rich help me again please..
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Thu Nov 06, 2008 3:44 pm

Re: Offset problem with TFM-55?

Each time I turn it on and off it increases a little. It got up to 98 V and drops a little to 94 after some mins.

Is this because the big caps are new or one is damaged?
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Thu Nov 06, 2008 3:58 pm

Re: Offset problem with TFM-55?

No negative dc offset anymore. it seems to be charging up a little more each time I turn it on. :-k :-k :-k

Maybe this would happen if there was a cap not working to full capacity.
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

RichP714

SILVER-7t

Posts: 1814

Joined: Fri Oct 12, 2007 2:12 pm

Post Thu Nov 06, 2008 3:59 pm

Re: Offset problem with TFM-55?

brit01 wrote::( :(

Well now after changing most of the small and large caps we have a new problem ](*,) ](*,) ](*,)

The dc offset has been reduced from 32 to 20 which is great BUT the good side that was just 3-4 mV is now showing a NEGATIVE offset of about 4 mV. Bias both sides if fine at 2.5mV.
sounds like the offset didn't change magnitude, just polarity; shouldn't be a problem

brit01 wrote:......AND the rail voltage will only rise to 83 (E4)Volts Max! I have tried adjusting it from the V1 trimmer but it does not change the voltage which is the most worrying part. And E3(22V).
This is significantly bad; worse, in fact, than your original problem

brit01 wrote:......One of the big caps damaged maybe? (Now C505/c506/c509 were taken out and I put the old ones back in today because my mail package with the new caps is going to be another week) My impatience. I could have damaged one of the old caps taking them out. maybe a result of the rail voltage??....
There's no sense in continuing to troubleshoot ANYTHING until the rail voltage prblem is fixed.

This can be alot of things here. A component in the amp section could be drawing the rail down so far it isn't adjustable. A component in the traic control could be bad, not allowing the triac to fire enough to meet the rail voltage. A component at or after the power supply filters could be dragging down the rail. The rectifiers could not be providing enough current to meet the rail. It could be alot of things.

It's most likely something you changed or removed. Go back and check your work. Check for shorts to nearby traces. If, after un-doing verything you did, it's still not working, then we'll have to start anew troubleshooting the power supply.

Oh, and never change too many variables without checking the results in stages (hind-sight in this case, but lesson learned).
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Thu Nov 06, 2008 4:09 pm

Re: Offset problem with TFM-55?

Oh, and never change too many variables without checking the results in stages (hind-sight in this case, but lesson learned).


yes very true. I was thinking this now. Lesson learned well.

Seems to have stabilized at around 93 V. The pot does adjust it but no more than 93V.

A component in the traic control could be bad, not allowing the triac to fire enough to meet the rail voltage


Which part is the triac control?


Go back and check your work.


I will do this and let you know.

Update: I'm suspecting the ceramic caps I changed. I think they gave me 50V ones! I asked for 100V but for some reason I didn't believe them
THEY ARE VERY HOT!!.
I will change them now. C208/C210.
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
<<

RichP714

SILVER-7t

Posts: 1814

Joined: Fri Oct 12, 2007 2:12 pm

Post Thu Nov 06, 2008 4:31 pm

Re: Offset problem with TFM-55?

brit01 wrote:.....
Which part is the triac control?.....
The triac control circuit is what regulates the rail voltage; it's no single component, but rather a network. Feedback is take from the rails through an optocoupler, who's output level nodifies a little oscillator stage that allows the triac to conduct more, or less depending on demand.

Sounds more like the rail is sagging due to recent work, rather than the triac control circuit not operating; we'll hold off on looking into this unless things go south from here
<<

snarffydoggy

User avatar

SILVER-7t

Posts: 1114

Joined: Tue Feb 12, 2008 7:29 pm

Location: Fairhope, Alabama

Post Thu Nov 06, 2008 5:17 pm

Re: Offset problem with TFM-55?

Allright things are livening up, it was starting to get awful boring
snarffydoggy
<<

brit01

User avatar

TFM-45

Posts: 589

Joined: Sat Jul 12, 2008 3:29 pm

Location: Montevideo, Uruguay

Post Thu Nov 06, 2008 5:30 pm

Re: Offset problem with TFM-55?

Hold on. Hold your horses.

Think things are back to normal guys.

I changed caps C301/302 and this boosted the rail.

The old ones were 270pF and I put in 470 pF as it states in the schematics.

maybe you can't always rely on the schematics!!

Let's see. I do some more testing but things seem all ok again (such a small component)

:D :D :D :D :D
TFM-55, CT-3, Klipsch F-1, Rotel RCD 930AX
PreviousNext

Return to CARVER Equipment Repair/Help Forum

Who is online

Users browsing this forum: No registered users and 2 guests

Powered by phpBB © 2011 phpBB Group.