Ah ! Njoe Tjoeb fault

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IslandPink
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#1 Ah ! Njoe Tjoeb fault

Post by IslandPink »

My venerable CD player is not giving any output from its analogue section now.
I mentioned this to Nick a little while back.
I hadn't noticed because I was just using the Coax out to the Longdog DAC.
Nick suggested checking the valves first ( 6922 ) in case they'd worn out, or filaments had parted.
I checked these today, they weren't lighting up, but checking the valves , they had similar and believable resistance. Then I noticed that the DIY front-panel LED that's connected to one of the filaments was off ; and sure enough the filament connections on the board are showing nothing, either DC or AC.
Looking for ideas where to look next.
There is nothing obviously burnt, or any caps showing domed tops.
Here's a picture, sorry this is a bit dark, but it does enlarge quite a lot.
The Toroid upper right has secondaries of 6V 2.5A and 28V 0.54A.
I'm not sure what the EI transformer to its left delivers, but where it comes onto the main board, the connector has voltages of 5V and 10V and possibly 26.5V marked on the board. So I'm a bit perplexed where any HT comes from, for the 6922's, but maybe they are only run very low, eg. 40V or something.

The transport appears to work and the CD's read - I haven't had it on with the DAC just recently but I believe the digital section is still working.

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#2 Re: Ah ! Njoe Tjoeb fault

Post by Dave the bass »

Resistor or PCB track/interconnect open betwixt filament PSU and valve would be my guess.

I'd check the filament PSU is working 1st then work towards the valve if it were me.
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#3 Re: Ah ! Njoe Tjoeb fault

Post by IslandPink »

Yeh - so would you suggest trying to follow the 6V winding from the toroid into the board and having a close look at anything downstream from there ?
A 2.5A winding seems overkill for that job, but I'm not clear what else would need the 6V. Maybe it's used for a number of things.
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#4 Re: Ah ! Njoe Tjoeb fault

Post by Nick »

I'm not sure what the EI transformer to its left delivers
I would guess looking at it that the EI is the original transformer for the CD player before the valve stage was added. The mains in seems to split to the EI and the toroid. Does the relay on the board by the toroid switch? I wonder if its job is to power the valve section up when required by supplying mains to the toroid, Naybe driven by the two wires from the main board to the board with the relay.
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#5 Re: Ah ! Njoe Tjoeb fault

Post by IslandPink »

Aha OK makes sense.
Yes the relay does click, and there's a fuse next to it which looks intact... or so I thought...
Just as I was writing this, I got up and decided to check the fuse with a multimeter, and it seems to be open. :)
This could be an easy fix if I can find something similar in my stash.
I'm not sure if there's any other fault, with a bit of luck it might just be age and a lot of transportation that has broken the fuse.

Edit : T160mA. Should have something , I bought a fair few packs of quick and slow blow in last few years.
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#6 Re: Ah ! Njoe Tjoeb fault

Post by Nick »

My guess is that fuse is in line with the toroids primary. Worth trying a replacement, if it blows again, its either the tx or what the tx supplies, so that’s where to go next. My money is its just the fuse.
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#7 Re: Ah ! Njoe Tjoeb fault

Post by IslandPink »

The closest I could find is 630mA. However I put one of those in and watched for a while , nothing untoward happened, and the valves are lit up. I'l confirm music later when i get chance, also order some 0.16 or 0.2A fuses. Thanks !
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#8 Re: Ah ! Njoe Tjoeb fault

Post by Nick »

Could have gone wrong, but didn't so that sounds great. May just have been the fuse eventually giving up from the transformer inrush.
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#9 Re: Ah ! Njoe Tjoeb fault

Post by Toppsy »

Mark,
I also use a Njoe Tjoeb CD player though mine is fitted with the TjoUpsampler in place of the op-amps.
Please be aware the fuse you are replacing IS NOT a 160mA slow blow BUT A 250mA slow blow, this despite what is printed on the circuit board.
The input and small circuit board is exactly as yours and is set up for UK mains input voltage. I have checked the value of the fuse under the clear plastic cover and it is 250mA. I have never replaced this fuse. So this was fitted by AH! when I ordered the player way back in 2002.

To quote from the known problems in the AH! Technical Support manual that came with the player:

My Njoe Tjoeb has no output. The tubes do not light up. The display is on.
You have a blown fuse. Find the small circuit board next to the power transformers. On that board is a fuse under a plastic cover. Remove the fuse and replace with same value fuse. For North American plyers (120v), the fuse is 500mA (milliamp) slow blow. For 220v players, the fuse is 250mA slow blow.

If you don't have a copy the Technical Support manual I could post to mine and so you can photocopy it at work. Being retired I don't have access to a double sided copier any more.

Hope the above helps. I'd hate for you to replace the blown fuse with a 160mA job and it blow straight away. This is likely to cause you to look for other unnecessary issues.
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#10 Re: Ah ! Njoe Tjoeb fault

Post by IslandPink »

Thanks for the advice Colin, interesting. I actually looked closely at the fuse I took out ( before reading the notes on the PCB ) and in fact it was a 160mA one. It may be that they started recommending 250mA for those who have the upsampler board ( which I don't have ), if that is also powered from the toroid ?
I have already ordered 200mA ones, so hopefully, given that I got 18 years of good service out of the 160mA fuse, i should be OK :)

ps. I'm getting music now, just to tie up that loose end.
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#11 Re: Ah ! Njoe Tjoeb fault

Post by Toppsy »

I don't think it has anything to do with the Upsampler upgrade module.

If you don't have a copy the technical support document you can find a online copy here: It makes reference to the fuse values for 110-120V and 220-240V versions on several pages. https://web.archive.org/web/20150220020 ... 3-enhp.htm
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#12 Re: Ah ! Njoe Tjoeb fault

Post by IslandPink »

Thanks for the document - good info to store. There must be a small amount of power required to run the upsampler.
In any case, I have ordered 200mA fuses already, it should give me a little extra margin, I will see how it goes.

ps. It may be after a while, with people swapping valves, they found 160mA was marginal. If it was specced for Philips 6922, you can see that ECC88 and 6DJ8 have a 20% higher filament power.
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#13 Re: Ah ! Njoe Tjoeb fault

Post by Nick »

IslandPink wrote: Mon Jun 21, 2021 10:08 pm ps. It may be after a while, with people swapping valves, they found 160mA was marginal. If it was specced for Philips 6922, you can see that ECC88 and 6DJ8 have a 20% higher filament power.
IMHO, it won't be the actual current draw of the system thats setting the fuse size, it will be the inrush current. So it may be as you said, they assumed 160ma would be fine, and then started getting them blow on power up (as you probably did) so increased the rating.
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#14 Re: Ah ! Njoe Tjoeb fault

Post by IslandPink »

Yes it's on the primary side, isn't it ? Good point.
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