Pioneer RT-701

Q

quayhog

Member
I recently acquired a RT 701. It appears to be a clean and well cared for machine. It plays back pre recorded tapes great. I try to make a recording and one channel is weaker on the VU meter and it plays back very fuzzy and distorted.

Are there any known issues and suggestions for an easy fix? The heads have very little apparent wear. I did need to clean the monitor switch before it would play or record. The tape path is clean.

I tried two different input sources and swapped channels on the playback. The distorted channel stays on the left channel.

I will need to open the recorder, the tape counter doesn't work, I have a new belt and capstan on order. I can clean switches and pots at that time.

I don't really know much about tape recorders but I have built and repaired a lot of tube amplifiers.
 
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Nice find! It's a great machine and there are plenty of 707 and 701 owners around here that can help you. I would wait until all pots have been cleaned and the new pinch roller is installed before I would rush to judgement. I would also have another look at the heads with a magnifying glass to see if you missed some deposits.
 
Hello and yes you are heading in the right direction. Cleaning everything and ordering new belts and new pinch roller. You probably already downloaded the service manual from hifiengine.

And if you are like most while waiting for the parts perusing the schematics looking at the audio path and such.

The only thing I would suggest is to re-clean the tape monitor switch also like Vince1 has suggested is to really clean those heads.

Will be waiting with popcorn on the side to see how it all goes. :D
 
I'd clean the pots for the input as a fist test. If that doesn't work clean the heads and if that fails a recap might be in order.
 
On the rear by the input connections are two output selection knobs. Be sure both are set at 0 or the same number, at the very least. Also, be sure your input control dials on front are both set at the same level.
 
Warpserver said:
I'd clean the pots for the input as a fist test. If that doesn't work clean the heads and if that fails a recap might be in order.
Click to expand...

On my RT-707's, this was critical. The input level pots have to be clean.

Also, set the MIC input pots to zero...it shouldn't cause the issue you're describing, but it can add noise that you don't need since you're not recording from the mics.
 
Hi,

With the monitor switch set to source is there any sign of distortion or fuzzyness there. With the VU meters on scale of course. If this signal is clean then there is no point in cleaning input pots etc as they are not causing the distortion.

Set up the machine for recording with monitor set to source. For this test leave the level slightly low so that you are not overloading the tape with signal in the first place.
Start the machine recording and then set the source switch to tape so that you can then hear the recorded results.

Do the following.
Whilst the recording is in progress. Change the speed switch from one to the other. Ignore the obvious speed errors but pay attention to the distortion. The Bias Osc power is modified by the speed switch along with equalistaion. If this seems OK, do the same with the Bias and Equalistaion switches themselves. If you get a strong reaction to any of the 3 switches it give you something to home in on, sort and rule out.

I think that the Bias/Equalisation switches will be the beasts as the problem is on the Left Channel only from your description.

Next one down the Bias Pot for the left channel. Don't touch this unless you have to. A slight tap with the handle of a small screwdriver but nothing more at this point. This needs speciality gear and test tapes to set up properly.

Then it is switching transistors for equalisation. If these are the error I would expect one speed, one setting of equalisation to be apparent.

I am OK on the RT 707 as I have owned one. The 701 is similar but not as much as they say. I do have a circuit for the 701, I will have a look see and if anything else springs to mind I will let you know.

By the way, the switches do tend to be self cleaning if moved regularly. At the start of every month (ish), I used to change the state all the switches and then return them to where they were. Then I would power it up.

Keep going, when running these are fine machines indeed.

GPS16
 
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Problems are mounting.
As before Record left very distorted, right ok. Plays pre recorded tapes ok. Defect does not follow source when alternating signal jacks. Same issue when using front mic jacks.

A second fault, possibly more troubling just started, is the relays that hold FF/Rew and play do not hold. Releases after about five seconds. Pause stopped working. If you hold the latches past the the time of fault it will rewind the tape.

Are there any good repair shops near San Jose (palo Alto)?
 
Hi,
there are no relays which hold in the operating switches. There is a release solenoid which trips them out after approx 5 secs as you have stated.

Next to the record head there should be a thick wire loop which the tape hold up when running. The loop is on a viscous damped pivot which gives the 5 secs before the release solenoid gets operated by a switch which the loop operates when it has reached the bottom.

Look more closely here for the latching difficulties. Is the tape being threaded correctly. Is the loop present????

You have not said whether the left signal is fine when the monitor switch is set to source. If this is OK, the input circuitry is fine and the fault is on the record side.
If when set to source the distortion is present then the machine is just recording what it is given.

Cheers

GPS16
 
The monitor sources with: source is clear. Recording is distorted.
I swapped the source from CD player and iPod. I swapped left and right RCA leads at the input. I also recorded through the front mic inputs. No combination changed the channel or record quality.

I still need to reexamine tape path for the second issue. It came on very suddenly. I'll try again later today. When my belt/capstan kit gets here I'll have better access to the front pots and switches.

Cosmetically the recorder is worth saving.
 
Hi,
those recorders are worth saving, period!!!!

As there is only a problem with the LHS channel on record, the first thing I would do is locate the Bias Pot for the LHS channel. If there is no bias then you will get distortion straight off.

I am on night shift at work at the moment and the circuit I have of the 701 is on my PC at home.

As you have tried all speeds and settings of the Bias/Eq switches and not found a good one, this still points to the Bias Pot as the most likely culprit!!! When I get home I will have a look and take things from there. If you have the circuit yourself, locate the Bias Osc and look at the secondary windings. From one of the windings there is a series capacitor with pot in series with that. This then feeds into the record head after the audio has been added. Find the pot for the LHS channel and check it for damage. Do not move it if you don't have to. As mentioned previously, at this stage I would try a small tap with the plastic handle of a small terminal screw driver. To set this pot up properly needs test tapes, frequency generators and HF volt meters etc.

When I get home I will see if I can find the description which is printed on the PCB.

Keep going. As said before, these are fine machines when running properly.

GPS16
 
GPS16. You were right on about a mis thread and the auto shutoff bar. I've been cleaning and inspecting heads and I had the cover off. Some how I got the tape on top of the bar. Functions OK know.

I'm waiting for counter belt to take the front off. I need to clean the pots. I hope I don't have a bad cap or transistor.
 
You might also try tapping on the record relays (two little white relay boxes on the osc. circuit board) and see if your left channel clears up. These are known troublemakers in both the energized and de-energized positions and they often need to be cleaned up after all these years. IIRC they are labelled on the schematic as something like RY301 and RY302 maybe?
 
Audio jones, I'll try that when I change the counter belt. I'll have it on the bench. Right now it's bolted to an audio rack.
 
I have the counter belt and roller replaced. A good look at the heads and they appear very shiny with no apparent wear. I haven't plugged it in yet for a test. I don't want to haul it back to the living room yet.

Are there any other maintenance items that should be done while the covers are off? Lubes etc. I cleaned the switches and pots real well with DeOxit. They looked like a previous owner used the Radio Shack pot spray that leaves a white film. I cleaned them up as best as I could. I hope that was my distorted record issue.
 
quayhog said:
I have the counter belt and roller replaced. A good look at the heads and they appear very shiny with no apparent wear. I haven't plugged it in yet for a test. I don't want to haul it back to the living room yet.

Are there any other maintenance items that should be done while the covers are off? Lubes etc. I cleaned the switches and pots real well with DeOxit. They looked like a previous owner used the Radio Shack pot spray that leaves a white film. I cleaned them up as best as I could. I hope that was my distorted record issue.
Click to expand...

Detach and clean the contacts at the Molex connector on the board on the top right side of the unit. Many speed control issues have resulted from oxidation there. Lube whatever moving parts you see, but remove any gummed up old grease first if present.
 
I've lubed what I can, contact points on levers. Just a hint of silicon grease made for luring "O" ring seals inside aircraft engines. I put a little on a q tip. Any tip on best getting DeOxit into switches for best effect?

Lube the motor bearings next. Two drops per motor? Lube point on play motor location?
I'm waiting for some oil, should be here today.
 
You might want to hold off on lubing the motors, just yet. After lubing mine I read that they are not meant to be lubed (maybe on the "tapeheads" forum, I can't really remember). Anyway, I thought I would throw that out there,even though it will probably cause a controversy. Also, mine doesn't seem to show any ill effects from the lubing, a few months ago.
 
Hi,

the reel motor on my machine had oil holes in the bearing end caps. I understand that not all do. If the holes are there I would put a few drops of light machine oil.

For the capstan motor, hang fire for the moment. I had speed control issues on mine and I know for a fact that the lubrication on Revox Capstan Motors is specialist. If lubrication is present you may do more harm that good by cleaning it off and replacing it with something inferior.

GPS16
 
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