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Bender Comments Page


These are Reel to Reel Questions, Answers, and comments, things I've posted on several discussion groups, some when people write and ask me questions.


************ COMMENTS PAGE 13 / ABOUT REEL TO REEL TAPE RECORDERS AND TAPE DECKS ************

Comment #60

Subject: Fix and Adjust the Akai GX-266D

Date: Sat, 15 May 2004 17:12:17 -0400

From: Frank Oomen in .nl

Hi Steven,

Saturday I fixed my GX-266D which had three blown transistors and two blown diodes of which one was a zener. I think the first part caused the second to blow which caused the third part to blow etc... This is what we call the "domino effect" here.

Then I also readjusted the in - and output levels. Just like the GX-650D I also had some strange experiences here. While the right channel got turned down to 0 VU reading exactly during readjusting the input (recording) levels, the left channel didn't get any lower than +2 VU and the potentiometer was completely turned counter clockwise. The potentiometer for the right channel had many degrees left so it was absolutely not fully turned counter clockwise.

********** And Bender Sez: **********

I think Richard Nixon and Henry Kissinger were the first users of the term "Domino Effect" WRT Vietnam... and boy was that a mess... of course, another boy has started a whole 'nuther mess of his own in Iraq, hasn't he... ? But now back to Tape Decks...

Ya know, I'm NOT A BIG FAN of crankin' those internal adjustment pots. Yeah, I know that Akai didn't paint them in position, like they did with the tape head alignments, but a few words of advice here on what I pretty much adhere to... Assuming first off that no "techie-wanna-be-idiot" has gone in there before you and totally messed things up...

I say mostly, leave it alone, often there are interactions between different areas of the circuit, and maybe at the factory they adjusted the whole things for the lowest distortion, and not precisely for the levels seen in the Service Manual ( or one could hope that the settings seen are the correct points for both ).

If someone has definately gone in and messed things up, well then you are in a "tough dog" situation, kinda damned if you do, damned if you don't... then follow the Service Manual. Hopefully, the "transiration" was done really well, and corrected by a native speaker of english, but I'd still consider the following...

If you figure that the arc of rotation on a typical internal control is around 220 degree's... if you have to crank that control more than 10 degree's in either direction to get something to measure properly... either that which you are measuring is wrong, or the control you are using is wrong for that task, or there is something else that is very wrong in that circuit. In other words... DON'T.

I recall a GX-630DB, a fellow gave me after he gave up on it. When it came in to me I removed the case and found to my dismay... a mess of wires unsoldered and dangling off of the bottom circuit board, which was the Dolby B encode / decode system. Beyond those maybe twenty wires just hanging out all over, seems he had taken to replacing the resistors on that circuit board with 1% metal film parts, likely in an effort to improve something, signal-to-noise ratio, I suspect.

Unfortunately, that didn't work. Once I obtained the service manual as this was like six or seven years back, I soldered all the little wires back to where they belonged, and still no signal passed in or out of the set. The VU meters simply didn't respond to any reasonable levels of audio signal on "Source" and nothing came out of the output jacks or headphone jack no matter how the set was operated, in "source" or "tape".

Actually there was a hint of a signal from some pre-recorded tapes, so faint, one could just detect it was there.

Well not being one to twiddle the little controls, I measured some signals, and found that at some point, in both channels, it simply disappeared. Puzzled, I then powered off and compared readings across some of the resistors against the values in the service manual.

Seems he had replaced an input resistor which was like 47,000 ohms, with one of 47 ohms, and since then, all signals entering the dolby board were quite precisely shorted to ground, by a factor of about 1000 to 1; so no amount of adjusting the pots would have made any difference if I had tried.

I had that set about five years, and I think I never did adjust any of the little pots inside, as it worked fine, later on, once I replaced a bunch of audiophile resistors with ordinary, plain ones... of the correct value.

--

Steven L. Bender, Designer of Vintage Audio Equipment


Comment #61

Subject: Re: Akai GX-747 dbx

Date: Thur, 27 May 2004 15:49:03 -0700

From: Jay Stills

Thanx,

I did see the wheel when I opened the unit up this past weekend to check the counter belt, which looked fine. Can you send me information on your repair service?? It sounds like a job that probably should be undertaken by someone with repair experience.

********** And Bender Sez: **********

Hi Jay,

Well I'm just packing a 747dbx up today that has been here for 6 months for repair of multiple problems... first its counter didn't zero at startup, it had recording problems level mismatches and in the reverse direction an intermittent recording problem where the recording would fade in, fade out, then disappear. Also there was a gawd-awful screech mechanically in fast wind and rewind so it needed repairs in many areas.

All of the mechanical and electrical problems were fixed and the set was setup for proper operation and now makes excellent recordings in both directions.

Basically I use a "3 check" method with a $75. minimum fee to evaluate the set, the first check covers the disassembly and evaluation $75. fee to discover what might be wrong. That first check is typically is $150. - $250. depending what problems are known by you and made known prior to my accepting the set for repair. This first check covers disassembly, evaluation, reassembly and "expected" repairs, and the first hour of labor.

2nd check is usually $100. and contingent on shipping damage, additional faults seen, which can be due to insufficient packing and/or faults that were overlooked, or previously not known, or more labor which was needed with an unexpectedly difficult repair.

3rd check is for return shipping and packing, typically $25. within 500 miles, or $35. to the midwest. When the set arrives, the first check is cashed. When all is known, and done, if the first check covered it, the second check is returned to you. When the set is ready to be packed, the 3rd check is cashed. If more work is needed than those items stated in the description of faults, which you will provide, then the 2nd check may come into play.

In addition, beyond repairs, I can also do various upgrades, such as cap replacements, and performance tests, one which checks and sets speed accuracy; another is checking that recording is equally phase-nulled between the two audio channels. Also a check on Wow and Flutter in either or both directions, weighted and unweighted; Record/Playback Frequency Response tests at various recording levels, in one, or both directions, and record/playback distortion levels at various levels.

Cost of these and other audio certification tests depends on which tests, and which levels, and whether for a single direction, or both directions. Typical set of Certification Tests runs from $50. for setting speed, checking Wow and Flutter (W&F) weighted and unweighted; and record/playback frequency response at a single recording level, to $150.+ for a full bank of tests, including Spectrum Analysis, and setting up the unit to be recording-optimized for a particular tape.

Occasionally such advanced tests as W&F unweighted; and Spectrum Analysis, show the set is performing well, but still needs additional work. Say if the unweighted W&F is perhaps double or triple the expected value, that may not be readily audible, but showing up on a standardized test, indicates the capstan motor needs replacement, which is a costly part; also, Spectrum Analysis cam show that certain caps and transistors in the circuit need replacement.

In the end, it all depends just how much you want to get to the "optimum performance" that can be obtained from the set; as most Reel to Reel sets are performing far from the best they could be - twenty or twenty five years later, even if they "look" brand new..

So if you want a quick fix, and the set returned in a few weeks, you'll have to try someone else, and today, most "repair experts" really have little idea of what they are doing, have no true understanding or these older sets, and no long-term service documentation. I'm slow and I don't work on many sets; and I would have a backlog of like 18 months worth of sets if I kept saying yes...

At this time, I no longer take many sets in for repair, except maybe when all existing projects are otherwise completed; at one point I had over 70 active projects and was getting nothing done on any of them. Now, I'm down to about six projects and working on them when I can. Mainly the sets I will take in are the RT-909's and GX-266II's, as no-one seems able to properly repair those but me.

On the GX-747's, Akai did not properly document some of the upgrades they had made after production in the sets, making it near impossible to do those things twenty years later. Certain fixes are not a problem, but your problem doesn't sound like one I've encountered before, and so it could be either a difficult or easy fix, depends what is found.

So at this point I am not taking any new sets in, perhaps that will change when I get two or three more projects completed and out the door.

--

Steven L. Bender, Designer of Vintage Audio Equipment


Comment #62

Subject: [Studer] A810 transport control quirks

Date: Thu, 25 May 2004 02:36:30 -0700

To: studer@recordist.com

Eric Jacobs Wrote:

I'm looking for a bit of guidance on two problems that I am having with my "parts" machine - I thought I'd take a crack at making it useable. It mostly works, but it has some quirks:

1. "Stop" does not stop. In fact, the machine speeds up to almost fast-forward speeds for 2-3 seconds, then slows down to barely moving, pauses, and then stops (you hear a "click").

2. "Trans" "Rewind" goes into this back-and-forth jerky mode (oscillates at about 120 Hz), never actually rewinding - it will oscillate forever if you don't hit another button. Regular old rewind works fine, as does "Trans" "Forward".

Any hints would be greatly welcomed.

Eric

********** And Bender Sez: **********

I may have never seen a Studer A810, but from the description, I would first check that all voltages and ripple currents in each power supply are both correct and within spec. If a PS cap has gone open, the resulting ripple and/or overvoltage can also cause functional problems which lead one to think its a problem in other areas. Check +5 Volt lines and also tantalum caps first with a cap meter and/or ESR meter with the set off; also time to check DC voltage lines visually with a scope.

Once all PS problems are ruled out... then it sounds like a faulty relay, if not hermetically sealed ( most aren't ) air pollution, sea salt, tobacco smoke, etc, can eventually cause contact problems in relays while arcing can cause the contacts to become/remain welded together.

Also check microswitches, some mechanism's may rely on lube for a mechanical sequence happening; like a sequential closing of a microswitch; if the lube is gummed up, the sequence may not happen within a normal time-frame, causing kaos. Also a faulty transistor, or diode within the logic can certainly be the culpret; or a bad cap. Unless the logic is totally IC's, in which case... then check for faulty soldering, or a damaged logic IC.

Having the schematics will certainly help you out.

--

Steven L. Bender, Designer of Vintage Audio Equipment

********** Going further... **********

Steve,

Thank you for the excellent recommendations. Capacitors are a common problem on vintage gear, and it seems that a cap/ESR meter should be a standard tool when working on these machines. I don't have such a meter, and was wondering if people might recommend their favorite make/model meter for this kind of work.

Eric

********** And Bender Sez: **********

I have two ESR meters and frankly that is overkill, I never got to use the second one much, and probably will take be an hour to find where I've put it. Neither unit is better than the other by much, just somewhat different. If you want the unused unit, it has a beep tone and analog meter, and is called the Capacitor Wiz. Aassuming I can find it and its paperwork, you can have it for half the original price, which comes to about $85. plus shipping & insurance to your location.

--

Steven L. Bender, Designer of Vintage Audio Equipment


Comment #63

From: "Ernie Betancourt"

To: "Steven Bender"

Subject: Still Here - Pioneer RT-909 Problem!

Date: Wed, 26 May 2004 20:01:04 -0400

Hi Steve!

Sorry I didn't get back to you when you sent me that email about several weeks ago. Anyway, it's good to hear from you. I have a situation that might be right up your alley. . .A friend of mine brought a Pioneer 909. I suggested that he not aught to have bothered with it, based on my experience of many units not working very well. My friend had the unit sent to my house first, whereby we could check it out and test it. I must admit, that the 909 is in good physical shape, but for some strange reason, the deck won't work in the forward "play mode!" Everything else works fine, except that there is no forward play!! Can't figure this one out. Now, here's the deal . . . I told my friend about your possibly being able to get the unit to play? Anyway, I told him that perhaps you might be able to either give him some insight or even repair the deck for him. He really likes the deck and is willing to pay a reasonable amount of money to have it possibly repaired. He's in no real rush to have it repaired per say, and says he simply likes the way the unit looks and its overall style. Please let me know what you can figure out on this situation. Personally, I don't like the Pioneer decks and I tried to talk him out of purchasing it. . .He won it on eBay. Let me know,

Ernie

********** And Bender Sez: **********

Hi Ernie -

In the Pioneer RT-909, there were several known failure modes over time. Unfortunately, the parts needed for this were having such high failure rates, they were discontinued by the OEM, and then Pioneer, eventually ran out of stock some years back of new ones, so no replacements exist. Due to that situation, I had special parts made up ( expensivo!~) so now I have these custom replacement parts, but only enough for repair of maybe another five or six of these Pioneer RT-909 sets.

Of course, there can be other failures in there, some also causing the same symptoms, but if this is the typical "it Fast Winds, but won't Play" failure, then yes, I can repair it. I have a minimum $75. evaluation fee to first disassemble and check to see if this is the failure my custom fix was designed for; if it is, then the evaluation fee and the total repair ( assuming no other problems are found ) comes to: $275.

If it turns out to be "something else" then the repair will cost whatever that something else requires to have fixed, maybe less, maybe more.

In addition, beyond repairs, I can also do various performance tests, one which checks and sets speed accuracy; another is checking that recording is equally phase-nulled between the two audio channels. Also a check on Wow and Flutter in either or both directions, weighted and unweighted; Record/Playback Frequency Response tests at various recording levels, in one, or both directions, and record/playback distortion levels at various levels.

Cost of these and other audio certification tests depends on which tests, and which levels, and whether for a single direction, or both directions. Typical set of Certification Tests runs from $50. for setting speed, checking Wow and Flutter (W&F) weighted and unweighted; and record/playback frequency response at a single recording level, to $150.+ for a full bank of tests, including Spectrum Analysis, and setting up the unit to be recording-optimized for a particular tape.

Occasionally such advanced tests as W&F unweighted; and Spectrum Analysis, show the set is performing well, but still needs additional work. Say if the unweighted W&F is perhaps double or triple the expected value, that may not be readily audible, but showing up on a standardized test, indicates the capstan belt or motor, or both needs replacement. The belt isn't a problem, but the capstan motor may not be available any longer, and was a rather costly part.

Spectrum Analysis can show that certain caps and transistors in the circuit need replacement. In the end, it all depends just how much he wants to get to the "optimum performance" that can be obtained from the set; as most Reel to Reel sets are performing far from the best they could be - twenty or twenty five years later, even if they "look" brand new..

Most "repair experts" really have little idea of what they are doing, have no true understanding or these older sets, and no long-term service documentation. OTOH, I'm slow getting things done, and I don't work on many sets; and I would have a backlog of like 18 months worth of sets if I kept saying yes...

So, at this time, I no longer take many sets in for repair, except maybe when all existing projects are otherwise completed; at one point I had over 70 active projects and was getting nothing done on any of them. Now, I'm down to about six projects and working on them when I can. Mainly the sets I will take in are the RT-909's and GX-266II's, as no-one seems able to properly repair those but me.

So while I'm not taking any new sets in, perhaps that will change once I get another two or three more projects completed and out the door.

--

Steven L. Bender, Designer of Vintage Audio Equipment


Comment #64

From: "Gianluca Pighi"

To: "Steven Bender"

Subject: Revox B77mkII Problem...make me crazy!!!! :(

Date: Tue, 1 Jun 2004 02:43:57 +0200

Gianluca Pighi wrote:

Dear Steven,

I've recently bought a B77mkII (15ips) in "perfect" condition..but I have a weird problem while recording material at 15ips: on the right channel I hear sometimes (randomly) some fuzzy and glitch but not continuous noise even without music!!! Sometimes it goes for some minutes sometimes just for 10 seconds: like a in and out disturb. It's strange because if I play the tape without anything on it there's no noise just a little hiss as expected from a tape recorder!!!

It makes me crazy, anybody in Italy seems to understand or has the knowledge to fix it. Can you help me?

I really appreciate your suggestion and I'll make for sure a Paypal donation for your (very useful) website.

Thanks in advance.

Best Regards

Gianluca Pighi

********** And Bender Sez: **********

While your description doesn't quite give enough detail for a precise answer, it seems likely if this happens only when recording and monitoring off the tape, that there is a contact or amplifying part which has become leaky or partially defective within the circuits of the recording section. I'm not quite expert on Revox equipment, but certain things common to complex electronic circuitry can be stated in general:

First... If the set has plug-in circuit boards, the plug-in fingers over time will tend to oxidize metal contact, whether tin or gold, can cause changes in voltage, or resistances at these contact points, usually from 10 to 44 contact points in a given circuit.. This leads to strange circuit behavoir.

The edge fingers with the contacts can be "shined up" for better contact using a lightly abrasive eraser found at the end of a lead pencil, or the usually rectangular pink, blue, or grey erasers one can buy separately. Often this will help if this is part of the problem. It is much more difficult to clean the connecting fingers inside of the edge-connectors, which do rely on a spring-action to provide tension and electrical contact, so this isn't suggested.

Second... Some number of capacitors in a given complex circuit will become defective after a few decades ( I have a fancy and very expensive lab quality Oscilloscope which had dozens of defective caps twenty years later... when I tested them, after replacing about 15 or so of these parts, the scope became operational again ). Luckily my cheaper scope never became so affected, and the backup scope always worked... I'm a big believer in having a "backup" :-).

Third... Transistors are not always forever, some small percentage will deteriorate over time, in ten to twenty years. Usually transistors when they fail, will fail suddenly, but that is not always the case... Akai had a couple of bad production batches of transistors, which became known only about 3 or 4 years after the sets were sold. These parts continued to get worse as time went on, in both magnitude and quantity of parts affected.

These parts would slowly lose voltage-gain, until they basically non-functional. So almost all later Akai RTR's made from between about 1979 to 1984 will have these "hissy-fit" transistors inside, and generally some 6 or more of these transistors will be found to be totally defective some 20-25 years later. Set symptoms include a terrible sounding rather high level of background hiss, or excessive distortion in one, or both channels.

Also some bridge rectifiers tended to short one or more of the four diodes, causing kaos in the power supply and the powered circuitry.

Fourth... Relays and Switches can have problems with their contacts, these can result as the after effects of exposure to: air pollution, sea salt, tobacco smoke, many things can affect the contacts.

While relays usually have gold plated contacts, and switches have silver plated contacts, problems can arise, some causing contact arcing, which wears away the contact points, and in either case, when the contact action goes from a normally low resistance to a high or changing resistance, and that consequentally causes artifacts in the circuitry affected.

Fifth... The power supply may have problems, if the capacitors actual capacitance has decreased in value, then normally regulated voltages may vary, or be out of tolerance, usually lower than normal, which can cause instability in some circuits.

Sixth... Wave Soldering or Hand Soldering is not always perfect, and can become affected by air pollution, and many other things, and soldering turned bad causes intermittants that are very difficult to track down. So there may be hundreds of potential points of failure in such a complex set, and only one lead has to be intermittantly making contact to cause a noise or problem such as the one you seem to be experiencing.

Given the high number of things that can affect complex circuitry, it is intrinsically difficult to guess what a minor problem is the result of.

--

Steven L. Bender, Designer of Vintage Audio Equipment


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Last Update - June 1st, 2004 5:30 PM.


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