Technics RS-1500US repair and service - my first Technics adventure

[smurfer77]

Well, it looks like the r2r bug has bitten. After getting my first r2r deck (Pioneer RT-707 thread) open and running only just over a year ago I am now close to finally finishing my 2nd r2r rebuild (Revox PR-99 thread).

I have had my eye on the Technics RS-1500US for a while and finally got my hands on one. It arrived with some minor damage to the rear panel (not the fancy wood on the sides, just the panel black panel at the very rear) that should be fixable. Well it was meant to be a runner. I turn it on and there are a few issues obvious within minutes, mostly dirty switches etc. One switch I will have to fix (the 2tk/4tk switch on the head block) as the lever is flopping around in the breeze and the connections for one channel are intermittent. Not too worried about that either.

The biggest malfunction I want to focus on upfront is that the speed runs full bore, irrespective of the speed switch setting. I've just printed out the manuals (sorry to the couple of trees I killed!) and will start studying the schematics. I haven't opened it up yet to check for obvious part failures... that is the next step. I hope to do a full mechanical service. In terms of electronics, are there any famous ticking time bombs that need to be sorted? Also, what are the opinions on the playback electronics compared to the PR99 (I mean specifically playback/output amp)? I will keep the PR99 stock (I think it sounds mighty fine). With the RS-1500 I am toying with the idea of custom playback electronics (a dedicated high quality phono amp modified with switchable NAB/IEC EQ?). I don't know, maybe i will keep it stock. Anyway, first things first, I need to get it running and service it mechanically. Any advice on suppliers of parts welcome - I know nothing about this machine. I know bottle head has a tape path kit.

Here is a pic - not too shabby! head have visible but moderate wear. At first it looked like the heads were rusty and scratched, but that was just massive junk build up - it was unreal that someone played it to that point!

 

[smurfer77]

Here is the shipping damage.

So I will straighten out the frame. And do my best with the chipboard....

Ok. I am impressed by the size of the capstan motor!

I had a poke around with the lamp/torch. No obvious burned up or leaking components.... just dusty. That is all I have time for today, but next time I am in there I will check the power supply then poke around the servo test points.

 

[GPS16]

Hi Smurfer,

Oooohhh! That is a very pretty beast!!.

My first steps would be check the power supplies for value and AC ripple. Tread very carefully until these have been verified. It would be a crying shame to "pop off" some Technics Silicon with duff supplies.

Next on the list would be to find the FG feedback and check it's presence. Until the Capstan is tamed, the rest of the machine is a low priority!!

As I have a A700 with Servo Tension Control, I am keen to see how Technics have implemented it. The Revox does this with transducers which do not "wear". Have Technics bettered it???

I will be following this one closely. Very nice machine!!!!!!

GPS16

 

[Grbluen]

Subscribed!

 

[phantomrebel]

First, congrats! Great deck, I own 3 variants. One thing I learned is that these decks, while mechanically solid, often suffer from cap rot. A full recap does wonders, and should be strongly considered (look for green legs on caps). I found this true of Technics amps and preamps from this era as well. Your headblock track selector switch issue may be easily fixed by bending some tabs back down if not too loose. Be careful here as they are unobtainable... see this video www.youtube.com/watch?v=HfB8Y4dpRoM . Other common issues: Brakes often need refreshing, and heads can show wear. The possible external preamp kits for this are enticing, but require a rather large financial commitment. Regarding your speed issue...have you cleaned the speed adjustment pot, pitch control, and speed selector switch? Do the lifters move freely and are tape tension idlers clean and lubed? These parts may get damaged in shipping: the faceplate scrapes by your tension rollers in the first pic is a concern. May also be dying caps. I'd at least recap the power supply board first. Worst case would be an IC on the main control board. Member Tinman is the resident expert on these decks...hopefully he will chime in.

 

[smurfer77]

Thanks everyone. I will get back with more info soon, but this morning I've just moved my PR99 from the workbench to the listening room and am enjoying some 2-track tapes!

Phantom, a couple of points I can speak to now: Visually the head wear is light (and straight). Nothing is clean or lubed on the unit... it needs a full going over. The right tensioner definitely took a hit at some point and that will require attention (it can be pressed towards the faceplate with much more ease than the other tensioner). Regarding the external preamp idea, of course my priority is getting the stock machine up to spec and listening to it before getting serious about that, but in principle I would not be purchasing one of the expensive ready made kits/devices for that. I have built a few phono amps in the past, with reverse engineered $5k MSRP phono amps, and got very good results for just a few hundred $, so it would not have to be a huge financial investment I think. In fact, I have a spare unit... and the work would really involve just the NAB/IEC EQ modifications.

Will get back in touch once Ive had a closer inspection of caps and checked PS voltages etc. But now, back to enjoying the fruits of my PR99 labor.

 

[Mrv8q]

Can't add anything electronics wise on this; until I saw your pics, never even seen inside one.

But I used one of these almost daily from 1983 thru 1987, in a cable network audio booth. Did many audio edits
using an Editall with the 1500, lots of analog fun. Bullet proof for years.

I made the move to video editing in 1987, but that 1500 and its twin were still working hard for years after.

 

[phantomrebel]

Thanks everyone. I will get back with more info soon, but this morning I've just moved my PR99 from the workbench to the listening room and am enjoying some 2-track tapes!

Phantom, a couple of points I can speak to now: Visually the head were is light (and straight). Nothing is clean or lubed on the unit... it needs a full going over. The right tensioner definitely took a hit at some point and that will require attention (it can be pressed towards the faceplate with much more ease than the other tensioner). Regarding the external preamp idea, of course my priority is getting the stock machine up to spec and listening to it before getting serious about that, but in principle I would not be purchasing one of the expensive ready made kits/devices for that. I have built a few phono amps in the past, with reverse engineered $5k MSRP phono amps, and got very good results for just a few hundred $, so it would have to be a huge financial investment I think. In fact, I have a spare unit... and the work would really involve just the NAB/IEC EQ modifications.

Will get back in touch once Ive had a closer inspection of caps and checked PS voltages etc. But now, back to enjoying the fruits of my PR99 labor.

Sounds like a great project! Please start a thread if you do the preamp....I'd sure be interested.

 

[KentTeffeteller]

There's a lot of electrolytics in this machine, and they're very well in need of replacement here. Many are very out of tolerance and/or leaky by now, the brakes also tend to need service on this machine as well. The power supply voltages are critical and are very important for the servo circuitry to reference to. This classic machine is well worth the labor to get running correctly again, and in good order is an amazing performer.

 

[smurfer77]

I am travelling now and havent had a chance to look into the RS1500 yet, but just had a question come to mind that i should research myself but maybe you experienced folk can save me a bit of time: on the Technics RS-1500 are the logic ICs unique or common?

 

[SaSi]

Hi, just had a look at the SM schematics and the logic ICs are plain NANDs. The exact IC is M53200P, which is equivalent to 74LS00. I think it's as common as it gets.

 

[dhnash]

The SM I have actually shows 3 different type of ICs:

IC 1, 2, 3, 4, 5, 6, 7 M53200P (14 Pin DIP, TTL Quad 2-Input NAND Gate)
IC 901, 902 M53273P (14 Pin DIP, Dual J K Flip Flop With Clear Circuit, IC for Frequency Divider)
IC903 M58432P (16 Pin DIP, IC for Crystal Osc, Frequency Divider)

The first two types of IC are common and replacements are easily found as SaSi said. The third type is a bit more difficult to find since it does not appear to be a common IC. Here is a website I found for a company that shows it as being in stock and available for delivery in the US:

https://www.utsource.net/itm/p/1708298.html

They actually show all of the ICs as being in stock and have a minimum order quantity of 1 and a minimum order value of $10. Their contact information is as follows:

USA Service
Address : 2321 W Norwood Pl. Alhambra， CA 91803 ，USA
TEL : +1 626 757 4001

 

[smurfer77]

Thanks for the responses on the ICs.

Didn't have much chance this week to do anything. I did clean the tape path, demag and just now I did confirm the PS voltages look ok. The 5V was down to 4.8V and I put it up to 5.05V. I exercised the speed select switch and variable speed pot a bit tonight. For a minute I did have something that was close to 15 IPS on the 15 IPS setting but slower speed settings reuslted in faster than 15IPS. After a minute it went back to 'normal' all speed settings result in something faster than 15 IPS. I plan to give all switches a proper clean when I have the machine apart soon. Next time I will poke around the servo board and see if anything jumps out. And, also I did see at least one electrolytic cap with the green 'furry' legs... so at some point I will make a cap list for an order.

 

[phantomrebel]

When you are ready to go for it, there is some good recapping advice and parts list in this thread:
http://www.audiokarma.org/forums/index.php?threads/technics-rs1500-tune-up-re-cap.566930/

 

[GPS16]

Hi Smurfer,

now that you know you have valid supplies, check the 2 adjustments for the Capstan Servo. There is one to set the to level of a ramp. The other is to position a Pulse on the ramp. These will centralise the "pull in" range of the servo. If these will not set up then you will know that you have a fault elsewhere.

Do the speeds work when Variable is selected? The reference then is a separate variable Osc and not a divided down crystal.

Cheers.

GPS16

 

[smurfer77]

Phantom, I will make my own cap list but thanks for the link, I had a read. I probably have all of the caps on hand, except the 10uF which I don't have in that quantity.

GPS, speeds do not settle down when I engage the variable speed button/adjuster. I see the two capstan adjustments you refer to in pg 21 of volume two of the manual at 1.5.E (Adjustment of Capstan-Motor-Control Circuitry). I set my scope to DC coupling and hooked up to TP907 and TP902 which are at the rear of the board as pictured in Fig. 25 just under the right hand side of the capstan motor so there was no need to dismantle anything yet. I see the ramp at TP907 which peaks at about 7.5 V. When I try to turn it up to 10 V is clipped out at about 8.3V. I turned it back to 7.5V for now.

And, at TP902... there is no pulse. At TP901 (just two transistors after the FG input to the board) we do have a sine wave. And the frequency of that looks good; just over 1kHz (15 IPS), 500Hz (7.5 IPS) & 250Hz (3.75 IPS). However, the amplitude of the AC signal is meant to be 3.1V (15 IPS), 1.6V (7.5 IPS) & 0.8V (3.75IPS) but I have about 1/10 of that. DC voltages around TR901 and TR902 are ok. And, now dinner is ready....I would like to find our what is going on, but I am seeinga few more suspect caps and do think it makes sense in this case to get onto all caps upfront. I also read similar advice from tinman and others regarding this unit.

 

[smurfer77]

Oh also there was a squealing noise during fast rewind that seemed to be coming from the counter mechanism. A single drop of oil on the shaft of the pulley nearest the capstan and that noise is gone.

 

[phantomrebel]

Oh also there was a squealing noise during fast rewind that seemed to be coming from the counter mechanism. A single drop of oil on the shaft of the pulley nearest the capstan and that noise is gone.

Yes, they all exhibit this and the fix, as you found, is very easy. More in this thread: http://audiokarma.org/forums/index.php?threads/technics-rs-1500.268483/

 

[smurfer77]

Caps have been ordered from Mouser and arrive on Saturday hopefully. Also do plan to get at those speed switches once again and completely disassemble them (for now I just gave a squirt of deoxit and exercise).

In the meantime I want to gather some knowledge on the motors. I have not decided if I will replace bearings until I inspect the motors more closely but is there any info out there on replacement bearings for the reels and capstan. I know the Capstan is tricky to reassemble and must be done in a particular way, but there is a quiet tick that can be heard from the capstan if I spin it slowly. i didn't notice it before. It can be heard about once every 2 or 3 revolutions; it is extremely quiet but it is there. This thread is pretty much the only one out there I found showing much on servicing the capstan or reel motors. Any other info would be appreciated, such as reassembly/alignment advice for the capstan, bearings for reel/capstan, lube type.

 

[GPS16]

Hi Smurfer,

if the bearings are Sintered Sleeve Bearings then you can only clean and re lube. They will be a press fit and will be destroyed if removed. Be very careful when dismantling the motors as there are plenty of coils in there which are giving feedback to the electronic commutation. There is an exciter set of coils and also pick up coils which feedback rotor position. As there is no direct feedback via magnets on the rotor, then ALL parts removed will need some kind of reference point so that they can be replaced in the exact position before they were removed. Errors here may affect the commutation and the torque produced per watt.

I am falling back on experience from VCRs, disc drives and robotics which I keep running at work.

You now have some experience of your own with dealing with the motors on the PR99. The capstan motor on the PR99 would seem to be the closest here as I don't think that there will be roller bearings!!! For the Reel Motors, I would use a lighter machine oil due to the speed of rotation. The Capstan I would be going for a good turntable type of oil which would be more viscous. This motor does not go fast at all.

If I am wrong in any of my assumptions then I am sure there are other AKers who will give more precise info.

On a "General" theme, there is my "3 pen' 'eth".

Cheers.

GPS16