Open Reel Dokorder 1140 recap - help needed!

[scokljat]

Hello,

A week ago I picked up Dokorder 1140 for a bargain of 60$. It's an open reel 4 track recorder from 1975. Very nice retro toy

Machine was initially very dirty and dusty but after some restoration, cleaning and lubrication, it looks quite good and fresh

Now, it works but have some issues. Intermittent noise when recording on channel 3, autosync feature not working properly on all channels, moderate hi frequency loss, lo freq. hum in some situations, etc... I solved lot of problems by cleaning contacts, relays and switches, but some problems remained.

I'm thinking about full recap. There is around 150 electrolytic capacitors inside. Most of them are Rubycon CE W series rated at 85 degrees C. On transport logic board there are bunch of Nichicon caps.

I randomly measured some caps with ESR meter, and they mostly show much higher capacitance than written on the cap (sometimes to 200%, usually 50%) with acceptable ESR value. Well, all these caps are 37 years old, after all. Device is ultra complex, lot of plug-in boards, relays, tons of cables and components...


My questions:

1. Do I really need to recap? It's a 37 years old device!

2. What capacitor type to use as substitute for Rubycon CE W? I found Rubycon YXF series quite appropriate. Any other suggestions?

3. Is it always ok to replace caps with higher voltages than original? E.g. there are some 47uf/6.3V caps on one board, than 47/16V on other board and 47uF/35V on third board. It would be much easier to install 47uf/35V or 50V on all boards.

4. What are these BIG aluminum Rubycon MP con caps with three terminals, A B and C, A-4uF, B-0.5uF, C-common, rated at 250WVAC?! (See pictures) Do I have to replace these too? What to use as replacement?


Few sets of these will solve 80% of my needs: http://www.ebay.com/itm/RUBYCON-YXF-...item2c69d36e62


Take a look at pics. Every suggestion is more than welcome!

And btw, I need service and user manual. Anyone?!


Thanks!

Cheers!

Suad

[budm]

Re: Open Reel Dokorder 1140 recap - help needed!

My room mate used to have one of this unit in the 70's, I myself had the TEAC 4-CH. His deck had a lot of problem due to the early day of not well made double-sided circuit board, same problem with SANSUI stuff that use this kind of double sided board, the feed through between the top layer copper to the bottom copper layer are really bad. We had to use small tinned gauge wires feeding through the feed through holes on the board to gt good connections otherwise you get noise and sound drop out.
Those old caps tend to have leakage which cause the DC current leakage between the audio stage so it will mess up the bias between the stages and loud pops and noises. They do not have to be low ESR type since it does not use switching power supply, just use good caps. I got rid all of my TEAC (3340s, 3300s) and Pioneer reel-to reel years ago, basically gave them away. You can use higher voltage cap as long as it fits. I also use Detoxit for cleaning swithces and pots. How are the heads.

[scokljat]

Re: Open Reel Dokorder 1140 recap - help needed!

My room mate used to have one of this unit in the 70's, I myself had the TEAC 4-CH. His deck had a lot of problem due to the early day of not well made double-sided circuit board, same problem with SANSUI stuff that use this kind of double sided board, the feed through between the top layer copper to the bottom copper layer are really bad. We had to use small tinned gauge wires feeding through the feed through holes on the board to gt good connections otherwise you get noise and sound drop out.
Those old caps tend to have leakage which cause the DC current leakage between the audio stage so it will mess up the bias between the stages and loud pops and noises. They do not have to be low ESR type since it does not use switching power supply, just use good caps. I got rid all of my TEAC (3340s, 3300s) and Pioneer reel-to reel years ago, basically gave them away. You can use higher voltage cap as long as it fits. I also use Detoxit for cleaning swithces and pots. How are the heads.

Thanks Budm for quick reply.

Well, you're right about double-sided circuit board problem. In this deck there are at least three PCB manufacture techniques. One is plain one sided PCB, other is this early double-sided PCB with some vias made with gauge wires feeding through the feed through holes, and there is one PCB (main transport logic board) produced in well made advanced double-sided technique usualy found in 80ties 8 bit computers. If I will do the recap, I'll take a look at solder joints and vias. Complete reflow/resolder would be ideal but too much time consuming. Even complete recap will be pain in the a_s because lot of caps are glued to PCB.

There are no visibly leaked caps, not in the way like acid spills as we find on modern devices. They are not bulged either, I found only one which was little bulged and I replaced it.

I don't use DeoxIT because it's not available in my country. I use German Kontakt Chemie - Kontakt 60 and Kontakt WL.

Heads and stuff look OK (see pics). There is little wear but acceptable. Whole unit looks like well maintained and treated with care and love. Actually, I took it from an old serviceman who is not in service for 15-20 years. I believe this Dokorder was not used at all for last decade or two, only collecting dust and waiting...

What caps do you prefer? I've chosen Rubycon YXF because they are available on Ebay, they're not too expensive and they have hi load life. Yes hey are low ESR but it can't hurt for audio? Right?

Thanks,

Cheers!

S

[midibob]

Re: Open Reel Dokorder 1140 recap - help needed!

Hi,
I just love all this old gear. At least it's repairable not like most modern stuff!

I would sort out the hum first as this is most likely due to the supply capacitors drying up. Of course this depends whether it's 100Hz or 50Hz hum. You can easily check with a scope to see if they need to be replaced.

They have two caps inside the same can (with a common ground) so direct replacement might be tricky although if you search around you should find something suitable. Are you sure the B cap is 0.5uF, that seems extremely low for an electrolytic!

I wouldn't bother recapping the whole machine, just replace any (or other faulty component) that you discover bad by fault finding.

Have you degaussed the heads and tape path?

Good luck
Midibob

[rhomanski]

Re: Open Reel Dokorder 1140 recap - help needed!

I am a member on an audio site as well as here. The consensus is to replace all the electrolytic capacitors. Which includes the tantalums. I'm listening to a Sansui system right now as I type. I've completely restored them. So far, I've restored six systems. Join up with http://www.audiokarma.org/ . They are friendly and very knowledgeable.

There are several transistors which are known to fail after all this time. They should be replaced on sight. I recommend using the google search on the Audiokarma site, it works the best. They have a lot of manuals for free download. Another place for manuals is http://www.hifiengine.com/ .

Regards,

Ron.

[scokljat]

Re: Open Reel Dokorder 1140 recap - help needed!

I would sort out the hum first as this is most likely due to the supply capacitors drying up. Of course this depends whether it's 100Hz or 50Hz hum. You can easily check with a scope to see if they need to be replaced.

Well, hum is present only in some situations and combinations and only on some channels. It's 50Hz.

They have two caps inside the same can (with a common ground) so direct replacement might be tricky although if you search around you should find something suitable. Are you sure the B cap is 0.5uF, that seems extremely low for an electrolytic!

There are three of these big caps. All three are same with three terminals. Terminal A, B and C. Look at detailed pics. Looks like A is 4uF, B is .5uF (with dot) and C is common. 250WVAC (what is W?) suggests it's for AC?

I wouldn't bother recapping the whole machine, just replace any (or other faulty component) that you discover bad by fault finding.

This machine is very complex. I was shocked when I opened it for the first time. Many boards ones on top others, complex cabling, 20 relays, even in meter bridge with VU meters are several boards on two floors! I think full recap is really needed as well as service manual. After recap and calibration if problems persist I should do fault finding board by board. It's almost 40 years old, so all caps inside are not what they should be. Recaping power supply first is a good idea.

Have you degaussed the heads and tape path?

That's a good question No I haven't, yet. I have a friend who will borrow degaussing tool so we will do it soon. Funny thing is that in my street, 150m away is a 100% analog recording studio with two 24track machines and several 2 track Studers as well as impressive amount of vintage outboard. It's the only studio like that in whole Croatia and it's next door to my studio The owner is friendly and he will help me with this one.

Good luck
Midibob

Thanks!

S

[scokljat]

Re: Open Reel Dokorder 1140 recap - help needed!

I am a member on an audio site as well as here. The consensus is to replace all the electrolytic capacitors. Which includes the tantalums.

Tantalums? Well yes! They like to burn when they're old Which ones are tantalums?! Sometimes with this few decades old equipment I have problems to identify some component types as they were quite different 30 years ago

Take look at the pics. I suppose tantalums are these small dark blue ones at bottom on first picture (4 pcs)? What are all these green caps on first and second picture?

Join up with http://www.audiokarma.org/ . They are friendly and very knowledgeable.

Actually I did! Searching for service manual. No response so far....

http://www.audiokarma.org/forums/sho...=308602&page=2

Maybe I'll open new thread on Audiokarma and copy/paste this one.

There are several transistors which are known to fail after all this time. They should be replaced on sight. I recommend using the google search on the Audiokarma site, it works the best. They have a lot of manuals for free download. Another place for manuals is http://www.hifiengine.com/ .

Please, tell me more about these transistors?

Thanks!

S

[midibob]

Re: Open Reel Dokorder 1140 recap - help needed!

I didn't look at those big caps closely enough!!
It does appear that they aren't for PSU smoothing especially one only being 0.5uF. Maybe they are used to control the motors if they are driven on AC?

Have to agree on changing the tantalums (the blue ones), always troublesome beasts.
The greens are normal polyester caps.

Good luck with a schematic, the only places I could find were chargeable but they did state they were original hard copies.

Midibob

[budm]

Re: Open Reel Dokorder 1140 recap - help needed!

Those silver can caps are the motor running caps.

[rhomanski]

Re: Open Reel Dokorder 1140 recap - help needed!

Tantalum capacitors are dipped and then painted after manufacture, so they usually look like little eggs. I have seen them in red, green, blue, and orange. They were used because they gave high capacitance in a small size. Even though they are very unreliable. Even today they have a high failure rate when they are manufactured. I replace them with either Nichicon KL series or Panasonic stacked film.

The transistors I spoke of were the 2sa725 and 2sa726 among others. They have a habit of getting noisy over time. Either causing a hiss or sometimes crackling noises or even motorboating. You can use a KSA992 to replace them. The pinout is opposite, so just put the new one in backwards.

Those blue aluminum capacitors I see should be replaced with Nichicon PW series. The modern capacitors are so much smaller than the originals, it will open up the boards. Although the lead spacing is closer. That isn't all that important unless the unit is going flying. One more important thing is to clean up all the glue on the boards. It may be corrosive and become conductive over all the years. I usually clean all the controls three times. When I first open it up, again while I'm waiting for parts, and finally before I put it all back together. That usually does the trick.

For the feed throughs, I use something like 18 gauge solid core wire or whatever size will fit the best. The point is to fill the hole as well as you can and solder both sides. It gives a more durable connection than just solder through the hole. The control board for the Sansui SC-5100 has to be done this way as well as two of the boards in my CA-3000. It takes a while to do all of them holes but is well worth it in the end.

Regards,

Ron.

[scokljat]

Re: Open Reel Dokorder 1140 recap - help needed!

Those silver can caps are the motor running caps.

That's logical. There are three motors, and three big silver caps. What type are this caps? Should they be replaced too?

Thanks!


S

[budm]

Re: Open Reel Dokorder 1140 recap - help needed!

When they are bad (lost its capacitance), the motor will stall and jerk instead of spinning. You should verify the value.

[japlytic]

Re: Open Reel Dokorder 1140 recap - help needed!

1. Considering the age of the unit (and the related hum problems), I think the electrolytics should be replaced.
2. Rubycon CE-W is a general purpose series, but it would not hurt to use low-ESR units.
3. Modern replacements are more compact than the older original units, so it is OK to use higher voltage units, which are no larger than the older original units.
4. The 3-terminal Rubycon unit can be replaced with two separate AC capacitors.

[Glenn G.]

Re: Open Reel Dokorder 1140 recap - help needed!

I bought a Decoder 1140 last week for $200 CDN along with original Dokorder tape up reel and 7 large reel tapes. I cleaned the tape path and attended to noisy switches but it will only play back on channel 1. In record mode the meter s indicate a good signal but on playback only 1 channel at very low level. Pre recorded tapes play loudly on channel 1 only. Any Ideas and suggestions are gratefully appreciated.

Thanks Glenn G

[scokljat]

Re: Open Reel Dokorder 1140 recap - help needed!

I bought a Decoder 1140 last week for $200 CDN along with original Dokorder tape up reel and 7 large reel tapes. I cleaned the tape path and attended to noisy switches but it will only play back on channel 1. In record mode the meter s indicate a good signal but on playback only 1 channel at very low level. Pre recorded tapes play loudly on channel 1 only. Any Ideas and suggestions are gratefully appreciated.

Thanks Glenn G

Well, this is very complex device. Did you remove all boards and cleaned connectors and contacts on them? In most cases you can remove connector and clean board edge connectors in place. Head assembly goes out as well and is plugged into an edge connector. This one is first to clean. The sync board (four switches above head assembly) is second to clean, it has two edge connectors and lot relays as I recall. Also clean two meter bridge connectors. Finally all relays must be cleaned (there is lot of them), luckily all have removable transparent plastic cap.

Take a look at my pictures from original and subsequent posts. If all of this doesn't help, then knock every board when playback a tape and look for bad solder joints and broken vias. And finally if nothing helps, test signal flow board by board and find source of the problem. For that you'll have to find service manual which I couldn't find.

I repaired mine to some point, but still have some crackle and hum. I gave up on total recap.

Whish you luck..

Regards,

Suad