Re-Capping a Pioneer CT-F900 Cassette Deck

This thread is a supplement to this thread: Rebuilding a Pioneer CT-F900 Transport

While the previous installment covered the rebuilding of the deck's transport, this one covers the process of replacing all of the electrolytic capacitors (caps) in the unit. This task is quite time consuming, and tedious, but proves to be well worth it in the long run, for various reasons, as I will discuss later.

Before performing this process, I strongly suggest completing the following tasks, to provide you a good comparative baseline for troubleshooting and assessing the value of your work:






The Pioneer CT-F900 contains 7 circuit boards, with 116 caps, and the parts cost for the caps alone is approximately $50.00. The labor for a good tech will likely be 12 to 15 hours, for the recap alone.

The unit you will see belongs to a fellow AKr. If he decides to chime in, you will be able to get his opinion as to value and changes in performance. Here is what the unit looked like when it was all done...



Rich P

Vintage Restoration Boiler Plate

First a bit of boiler-plate DIY info:

1. If you are an impatient individual, tending to get frustrated, and force things, or get rough. DO NOT attempt this operation. You could very easily wind up with a pretty, brushed aluminum paperweight. Generally, if a unit is fresh, and unmolested, it is less expensive for a knowledgeable tech to restore/repair. If I have to clean up a ham-handed, fumbled job, it will definitely cost ya.

2. Make sure that your tools are in good condition. For example, if the tips of your screwdrivers are worn, you will damage the heads of your screws (some are in pretty tight), and you will play heck trying to get them out. New screwdrivers make all the difference in the world. All it takes is for your driver to slip one good time in a stubborn phillips head screw, and you could make it next to impossible to remove, and you will damage your driver as well (take a look at your old phillips screwdriver).

3. Do not get curious about additional details of the mechanism. There are an abundance of tiny little parts just waiting to jump out of your machine and into the nether world if you are not careful or know what to expect. These little parts can be worth the entire cost of your machine, since, if you do not find them, or if you break them, you will have a non-functional unit.

4. Unless you have an idetic memory (photographic), take pics, notes, etc., as you go. It is not a good thing to have extra parts left over at the end of a job. I have a large supply of tiny zip-lock bags which I use to put parts from various stages of work. In this way the number of screws, or a couple of screws and a spring or c-clip will key my memory to the stage or assembly they go back into.

5. There are no magic bullet chemicals. Use each chemical or lubricant, etc., only where it is appropriate. If not, you have a paperweight again. If you are not sure what to use where, seek wise counsel, from reputable sources.

6. Before you do any disassembly or work, put a baggie over your power plug, and hold it on with a rubber band. The very last thing you want to do, is get surprised by a spark, or G_d-forbid, a jolt. Guess what...paperweight time again.

7. NEVER force ANYTHING. If you have to force it, you are not doing it right and you will likely break something, or get a part on wrong...paperweight time again (Getting irritated at that phrase? Good.).

8. Mickey Mouse has no part in a vintage restoration shop. NO half-tail operations, no funky monkey rigging, no time bombs for someone else to clean up. I cannot tell you how many times I have seen serious just enough to get by kind of repairs (blobs of glue to replace lost c-clips, weird wire twists holding on broken parts, etc.) If you break or lose something, buy a parts unit and replace it right. Chewing gum, bailing-wire rigs will ALWAYS come back to bite you.

9. There are innumerable tricks of the trade that are too detailed to discuss in a DIY thread (how to hold a tool, how to keep a c-clip from jumping across a room, etc.). Be prepared to learn some/many of them the hard way (by experience). Sorry folks, it comes with the territory.

10. Get a service manual. They are just too readily available to justify flying blind. If you are a cheap ________, buy one on CD. They are only around $10 on the bay. I prefer originals. The color coding in the drawings is a real help to an old man like me.

11. Go slow. Be meticulous. Double and triple check everything. It is easier to take the extra time to do it right the first time, than to have to take the time to troubleshoot and repair any mistakes.

12. When wires are attached to boards being worked on, try to tie them to the board, so that the wires will flex at the tie-point, rather than at their attachment points. This will keep you from making stressed connections that will break in shipment or later. Also, note wire bundle ties and remove them, to gain as free access as possible. You may be moving the boards around quite a bit, accessing top and bottom, over and over again. Please take special note, even photos, of which wires are in which bundles, and where they are ties in bundles. If you just bundle up wires to look nice, you could get wrong wires in close associateion with each other, and introduce hum or other kinds of noise or feedback loops.

Last but not least...I accept no responsibiblity for how well or successful you may be at performing this operation. Results will vary from unit to unit, and from individual to individual. You know...some folks should simply not try this kind of work. Most folks can be successful however.

Rich P

Re-Capping: Motivations, Considerations, Results

My experience: Recapping generally yields only an incremental improvement in the way a unit sounds, but should significantly increase the life-expectancy of a unit.

Here are your incentives/motivations, so balance them against cost and/or effort:

1. I have measured a large number of caps, replaced during a recap. The majority are at or below the low end of their specs, unless they are in a location where they get thermally stressed.

2. When 'lytic caps go, as the odds of doing so rises rapidly once their rated life expectancy of around 20 years has been reached or exceeded, they go any one of 3 ways, drift out of tolerance, fail open, or fail short. They all drift, and statistically, failing open or short is about a 50/50 mix.

3. If a cap fails open, you may notice, you may not, depending on where it is in the circuit. Generally the fault is easily repaired, with minimal peripheral damage.

4. The main risk: If a cap fails short, it can, and generally does, take out significant associated circuitry (ie. semiconductors made out of unobtainium).

5. Recapping is cheap, part-wise, averaging $0.35 per cap, but labor is high. A good tech can be counted to be able to replace around 10 caps per hour (including unit disassembly, cap removal, pad cleanup, cap installation, and flux cleanup). Even if the tech only charges $10 per hour, in a unit with 150 caps to replace (not uncommon on gear I work on), the labor really mounts up when it takes 15 hours to do the job. Typical modern labor costs are in excess of $60 per hour. AK restoration artists are not in it for the money (but money is nice), so we generally do not charge anywhere near that rate, but our labor is worth that rate.

6. The MOST IMPORTANT aspect of a recap, is the opportunity to refresh all circuit board solder joints. Flow-soldered connections have only about a 30-year life expectancy. In my experience, I have solved more problems caused by old, oxidized, fractured solder joints than by failed/drifted caps. Here is where the real bang for the buck is realized, and MUST NOT be underestimated.

With all of these aspects considered, recapping is really only a viable procedure for upper end gear, unless the gear owner is an avid collector, and wants all of a series in excellent condition, etc.

Rich P

Recapping Boiler Plate

Now a bit of boiler-plate recapping info:

Note: Most of the original capacitor series used in these old units are long obsolete. Selecting replacements, from current manufacturers and their series, is also a task requiring a qualified tech. There are many parameters to consider (operating temp, value, value tolerance, life expectancy, effective series resistance, internal losses, size, etc.).

I am a Pioneer specialist, so, all my work references the Pioneer parts series. This is because my master recapping database is based on Pioneer part numbers.

The problem with most vintage gear (in excess of 25 years old), is the fact that electrolytic caps tend to dry out, since the electrolyte is moist, and must stay that way for proper function. Some caps drift severely, in the lower capacitance direction. Some caps fail open, and simply cease to perform whatever function they were designed in to do. Others that fail, do so by failing short, generally causing catastrophic damage to the unit. You may be enjoying a ticking time-bomb. Some will swell and leak, causing all kinds of corrosion damage to the circuit boards in the area, while others will literally blow up. Some caps measure OK on a capacitance bridge, but, in the circuit, leak DC, causing noise, bias shifting, instability, etc. I truly recommend re-capping gear you intend to keep and enjoy, or sell to someone you care about.

Re-capping generally requires a complete service manual, with all published supplements, addendums, errata, and modification sheets. Each board is gone through, electrolytic caps are each measured to get their physical dimensions (replacements must fit in the space provided. Not to fear normally, since modern caps tend to be 1/3 the size of the originals (sometimes causing other problems)). Then the caps are checked to see which Pioneer series they are in (indicated by Pioneer part number). Now you must attempt to determine what characteristics were inportant to the designers that established a specific Pioneer part number series. Hints come from what cap manufacturer series was used (usually, and hopefully, more than one), "if" you can find the very old data sheets you need (so far all the series I've encountered have been long obsolete), or mfg-to-mfg cross-reference lists. You must also track what kind of circuits the particular Pioneer part number series is used in (coupling, de-coupling, filtering, feedback, etc.). Without the original Pioneer part drawings, you must engage in significant guesswork, supplemented by informed/experienced reverse-engineering.

The next step is to attempt to find modern manufacturers for parts that conform to the design criteria determined in the previous step, followed by locating distributors that handle the replacement parts (in the onesy-twosy quantities you will need), and determine the per unit cost. (Note: I prefer to keep things original. I don't try to second think the original designers, unless the future owner pays significantly for an upgrade or modification. I do tend to use a bit better part than the original, but not to point of using the very expensive, esoteric, sometimes snake-oil parts. It gets to be a lot of fun when the part you need is not made by anybody in the size and/or voltage you need (like finding low voltage electrolytics in the sub-1uf values). Then you need to substitute a different kind of part altogether.

I then created an overall Pioneer database for electrolytic caps, which I can then draw on for other models down the line, and from which, I create a model-specific database, which shows each cap, on a per-circuit-board basis, with all the associated info (original part number, dimensions, value, working voltage, new mfg part number, distributor part number, price, etc. etc. etc.). The database also contains a table of consolidated data, where all like parts are grouped, used as a purchasing list for the model.

Here are some of my choices for the various types of caps that may need replacement:





When I order the caps for a unit, I usually order enough to do 3 or 4 units, since I usually have at least that many units of any particular model in my inventory, and I like to have the parts I need on hand when it comes time to do them. That way, I also have complete recap kits on hand for incoming restoration commissions. I also usually order at least 2 extra of any particular cap value. In that way, my on-hand inventory of caps grows, at minimal cost, which helps to cover the cases where the manual states the need for one value, when a particular board/unit actually has a different value (happens when designs are changed during the production of a particular model).

Emphasis:

Recapping is not the panacea for modern man. Recapping is the last thing I do to a unit, other than cosmetic work and final/performance testing. I won't recap a unit, until I have determined that it is fully functional. Recapping is more for an attempt at adding longevity to the mix. The last thing you want is for a 30-year-old 'lytic to fail short (they also fail open, and drift out of spec). Recapping is not a good "repair" technique (falls in the realm of 'shotgun repair' which I hate).

Rich P

Supplemental Recapping Operations

I have done alot of recapping, and I like to test the old ones every now and then, to see what their condition was. In general, I have found that they are not far off, just at or below the capacitance spec for the parts. I have found a few bad ones. What I add, with a recap, is a retouching of every solder joint on the affected circuit boards. Here is where the real problem is, in my experience: old, oxidized, fractured, and cold, joints that have failed. The life expectance for a wave soldered joint (used in circuit board manufacturing) is right at 30 years. They tend to oxidize, and fracture, etc. I have repaired more problems caused by bad PCB solder joints, than by bad 'lytic caps, by at least an order of magnitude. So, for me, the solder joint retouch is the more important aspect of my recapping service.

When replacing a cap, I have found it to be best to remove the cap, then remove the solder from where the cap was. That way damage to the circuit board traces and pads are minimized. If you try to remove the solder, then get the board to let go of the cap, yu will find that there is too much heat, time, and stress on the circuit boards, resulting in lifted solder pads and traces. The best method I have found is as follows:






While you have a board loose, it would behoove you to desolder and remove any heat-sunk drivers, clean off the old heatsink grease, and apply new heatsink grease (I use Dow Corning 340). Be very careful to reassemble exactly as they were assembled. many drivers are electrically isolated from the heatsinks, using mylar isolators or some other method. If you don't put them back to gether the way they were, you will let the magic smoke out when you apply power later. Putting fresh heatsink grease on will help to keep your old parts cool so they will last longer. Old, dry, flakey heatsink compound does not do its job.

Note: Styrol (polystyrene) capacitors are extremely sensitive to heat. They cannot tolerate temperatures above 85 degC, and will be damaged is subjected to higher temps. Soldering involves temperatures in excess of 200 degC. You must clip a heatsink clip between the capacitor and the solder joint when retouching joints associated with styrol caps. To be safe, unless a magnified visual inspection of a solder joint, related to a styrol cap, reveals the need for reflowing (oxidized, fractured, etc.), I generally mark the solder joints in close proximity, on the same trace, with a red sharpie. This is so I will not hit them with a soldering iron during the solder joint retouch operation performed on the board, once all the 'lytics have been replaced on it. The sharpie ink is usually removed when I clean off all the old flux from the board, after solder retouch. The attached image shows a couple of styrol caps, so you can recognize them...



Rich P

Visual Overview

This first the first view of the job ahead. It is a "Before" view, and, and after view will be presented when we're done. Unlike other Pioneer models, most of the boards are pretty accessible, except for those containing the user controls. We will need to do a bit of extra disassembly to get at them...



Before you ask...Yes, my bench system consists of a TX-9500-II tuner, a SPEC-1 preamp, and a Spec-4 power amp. Imagine what my main rig is like

Rich P

Transport Control Board

Might as well start with the board that is raising its hand...

The solder side of this board is accessed by removing the 4 screw in the corners of the board. There is a hole in the transport bracket, to allow you to get the screwdriver on to the screw it overhangs. Recapping here is pretty straight-forward, except that you really need to tie the many wires to the board, so you do not stress their connections with the repeated board flipping.

Here are "before" and "after" pics. The visual difference is not too dramatic here, as the new caps are just about the same size as the old ones (typically the minimum physical dimensions for a 'lytic cap).





Rich P

Power Supply

Here you will see a much more dramatic visual difference, as is typical of power supplies. New caps are generally 1/3 the size of the old ones.

There is a bit of extra disassembly needed to access the power supply:



Again, secure the many wires to the board, to provide strain relief for where they connect. You don't want to break off wires and have to find out where they go, or have them break in shipping or later on.

While you have the board loose, replace the heatsink grease under the big drivers...





Rich P

Integrated Amp Boards

Next, lets tackle the integrated amps. They are soldered to the mother board, via edge pins. The first pic shows the boards, still attached to the motherboard. You will need to remove the solder from the pins, making sure each one is free from the motherboard, then carefully extract each of the 2 boards.



To access the motherboard's solder side, you rotate the unit up on its left side, and remove the 4 screws, securing the access plate from the bottom of the unit. The second pic shows the bottom of the unit, with the access plate removed.



The integrated amp boards have a couple of specialty caps:



The last 2 pics show before and after shots of the integrated amp boards...





Rich P

Motherboard

Here it gets a bit difficult, as some of the motherboard solder joints are located under the baseplate. You will have to desolder with solder wick here. Although difficult, with patience it can be done.

Please note that this board has several heat-sensitive styrol caps. Be sure to mark their solder joints and other thermally near joints with a red sharpie, so you sill stay off of them with your soldering iron. If you don't you will damage them when the joints get hot enough to melt solder (well beyond their 85degC tolerance for heat).

'Before' and 'after' pics are here, but you will not notice anything dramatic. Again, lthe caps are all pretty much at the minimum dimensions for 'lytics, to begin with...





Rich P

Indicator Boards

As I warned you at the start, recapping the indicator boards is going to be a bit of a challenge. Just be slow and careful, and all will go well..

The first pic shows the indicator with its face on (taken during initial testing, not during recap: Note power is on). The indicator face is held on by the 4 circled screws.



The second pic shows the indicator assy, with the face removed. The indicator boards are removed as a unit, by removing the 6 circled screws. Then the individual boards are removed from the assembly, for recap work.



The third pic shows the back of the indicator assy. The shield board is held on via the 3 screws, visible in the pic.



The fourth pic shows the 'after' shot of the indicator board, while, the last 2 pics show the 'before' and 'after' shots of the indicator amp board (pretty straightforward, once you are able to access them).






Rich P

Finished Visual Overview

Here is what the internals look like when the recapping operation is done. If you do it right, you will have no extra parts left over, and the magic smoke will stay in when you power it up. When you do power it up, be sure to wear suitable eye protection (goggles or special glasses with side and top shields), because caps in backwards tend to blow up, or shoot off the boards like bottle-rockets.



Now go forth and recap your CT-F900...

Enjoy,
Rich P

Great Job Rich. Just for the record to you have the total # of caps replaced for this unit? Also I assume the procedure would be the same for the 950?

Lefty

Very informative and detailed thread!

I would like to show my tech this. I have been battling a 900 for almost two years. I ordered replacement IC's, belts, pinch rollers, and finally - an entire display assembly w/board.

The first time I got it back from my tech, it played fine but the display wasn't calibrated properly. I took it back. He fixed the display, but now there was a repetative clicking noise.

It is back there right now. Hopefully I will be able to use it one day. :tears:

This is an awesome thread. :ntwrthy:

And I'm the proud owner of the 900 that Pustelniakr is talking about.


I'll just say this....it CERTAINLY outpreforms ALL my Marantz decks and goes toe to toe with my Nak LX5.......Works BETTER than it did new in 85.....


WORTH EVERY penny....Gonna have him do my RT-707


The man is an artist, he just works with silver....


Love to all....

Hey,
Have you ever considered selling recapping kits for these (and other) units?

TriumphEnt said:

Hey,
Have you ever considered selling recapping kits for these (and other) units?

Click to expand...

I have, but there are several gotchas:




Enjoy,
Rich P

Very good Job and explanation...thanks