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).

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).

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

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.

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

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.

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.

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.

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.


It's still fighting me.

Rich help me again please..

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?

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

Maybe this would happen if there was a cap not working to full capacity.

:(

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

......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

......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).

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.

.....
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

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

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)