Re-capping Incorrect Values?

[robbie010]

Evening all.

I have decided to go ahead and re-cap the control board on my pioneer deck as it isn’t running right after a service and new belt.

I’ve managed to get hold of a schematic and opened it up this evening, however, the specs of the electrolytic capacitors in-place are different to those listed on the schematic, in some cases, wildly.

Specs as stated on the schematic:

C201 & C209-C212 - .47uf / 50v
C202 - 1uf / 10v
C206 - 1uf / 16v
C207 - 47uf / 16v
C208 - 10uf / 16v
C213 - 33uf / 25v

Caps seen on the board:

.47uf / 50v (x4)
2.2uf / 50v
3.3uf / 25v
4.7uf / 25v
47uf / 25v
100uf / 16v
1uf / 50v

I’m struggling to cross reference the caps properly as the numbers are not individually printed on the board, but for the most part I can guess which is which.

Now, I understand that the voltage rating isn’t important but the capacity seems wildly different on some caps so I’m wondering whether to recap like for like or as per the schematic??

 

[Nopiano]

I know nothing about circuits like this, but is it possible you have a Mark 2, or some such, and the schematic is a mark 1? Or maybe some running spec change?

Otherwise, unless the board appears tinkered with, I’d have thought copying the original was a better prospect.

 

[robbie010]

I know nothing about circuits like this, but is it possible you have a Mark 2, or some such, and the schematic is a mark 1? Or maybe some running spec change?

Otherwise, unless the board appears tinkered with, I’d have thought copying the original was a better prospect.

As I understand it, the deck was only produced between 1972 - 1975, there are no differing versions of it.

I’m assuming the current caps are not original but not new either.

 

[Nopiano]

As I understand it, the deck was only produced between 1972 - 1975, there are no differing versions of it.

I’m assuming the current caps are not original but not new either.

Fair enough. Then I can’t help at all, Sorry, Simon.

 

[slavedata]

It's not uncommon. I just recapped a Rogers Cadet and some values were wildly different from the schematic. I think back in the day to keep production rolling they would use nearest values where it didn't matter often overspeccing on the subs. Just use the schematic values and you should be fine. Sometimes you have no option but to use an intelligent sub as the old value is no longer made.
Stick to at least the stated voltage rating or higher. The Rogers came out sounding great.

Good luck!

 

[karma67]

hmm would it not be wiser to go with whats on the pcb?

 

[robbie010]

It's not uncommon. I just recapped a Rogers Cadet and some values were wildly different from the schematic. I think back in the day to keep production rolling they would use nearest values where it didn't matter often overspeccing on the subs. Just use the schematic values and you should be fine. Sometimes you have no option but to use an intelligent sub as the old value is no longer made.
Stick to at least the stated voltage rating or higher. The Rogers came out sounding great.

Good luck!

Its seems odd that they would use caps so wildly out of spec, especially as this is the board that controls the motor speed……

I’ve managed to get a look at the underside of the board and done a little more research on the caps themselves. Its seems that the SL Series Chemicon caps are indeed original 70’s production caps and looking at the board the solder work certainly looks all original, so no doubt the caps are well past there use-by date! In fact, they are older than me!

 

[pmcuk]

As mentioned, the important thing is to use the voltage specified or a larger voltage, like using 25V working for a 16V part. I have no idea how the circuit works, but critical voltages are usually determined by resistors and solid state devices rather than electrolytic capacitors. So the capacitance values may not be so critical. That's just a general guess.

 

[robbie010]

As mentioned, the important thing is to use the voltage specified or a larger voltage, like using 25V working for a 16V part. I have no idea how the circuit works, but critical voltages are usually determined by resistors and solid state devices rather than electrolytic capacitors. So the capacitance values may not be so critical. That's just a general guess.

Thanks. I’ve ordered parts as per the schematic, as mentioned, matching voltage or higher.

The turntable has a DC servo controlled Hall motor and as I understand it, this control board continually corrects the motor speed in conjunction with the hall sensors in the motor.

 

[robbie010]

Just a little update on this….. and a question!

I pulled all 10 electrolytic caps tonight, one or two were showing signs of leakage on the underside and every single one measured more that 20% outside of the stated spec, one or two of them were measuring near on 70% out of spec.

Obviously, a good move to do the re-cap, but it makes me wonder…. Does an old, leaky cap that measures outside of its stated spec still function as intended?

The reason for the query is that I’m now convinced that these are indeed the original caps and near on 50 years old but some have always been outside of the specification stated on the schematic and the turntable must have functioned perfectly well at an earlier point in time…

It may well be as @pmcuk says and the actual capacitance of the caps may not be important…

 

[rabski]

You can never rely on schematics. Things change during production runs for various reasons, and frankly sometimes schematics are just plain wrong. Even the best, old manufacturer's published schemas sometimes have errors.

I don't know the circuit, and sand-based stuff is far from my forte, but I would recap based on what's fitted, rather than any schematic.

 

[robbie010]

You can never rely on schematics. Things change during production runs for various reasons, and frankly sometimes schematics are just plain wrong. Even the best, old manufacturer's published schemas sometimes have errors.

I don't know the circuit, and sand-based stuff is far from my forte, but I would recap based on what's fitted, rather than any schematic.

Seems odd though… I’ve had a real good look over the schematic and compared it to the board, every other component is as per the schematic, its only the electrolytic caps that are not in-line with the schematic. There are 10 caps in total and all but 4 caps are the wrong value, two of the 4 caps are pretty close but two are way out.

 

[lazycat]

Seems odd though… I’ve had a real good look over the schematic and compared it to the board, every other component is as per the schematic, its only the electrolytic caps that are not in-line with the schematic. There are 10 caps in total and all but 4 caps are the wrong value, two of the 4 caps are pretty close but two are way out.

Personally, I'd recap with what's in there. If this doesnt solve your problems then try the schematic values.

 

[Jazid]

Agree with Bencat and Rabski. If those caps were put in by the manufacturer and they worked then the values will have been considerd safe, and presumably it worked fine for 30+ years with them in there..

 

[JamieMcC]

Sometimes if a manufacturer has several products that use for example 50uf capacitors they may baulk purchase those and standardize them across several products in a range using them instead of lower values that might be shown in the schematic for a particular product this may improve performance say in a power supply where a lower value was specified.