Servo Error on Tascam md-801r

[Cesar fernandez]

Hello everyone..I'm in need of a Tascam minidisc MD-801R service manual..Can anybody help please?..The unit tries to read TOC information and then says "Servo Error"
The laser moves to the centre, illuminates but the spindle motor doesn't spin!.

[kgallen]

No service manual on this page: https://www.minidisc.org/part_Tascam_MD-801P+801R+801RMKII.html

It might be worth downloading service manuals for other Tascam MDs as at least one is likely to share the same MD drive. There is a time-line list at the top of the page linked above. The display looks like the one on my MD-350 so that might be a good start. 

On Sony machines I think the spindle motor is controlled from the main board. Not sure if this is how the Tascam units do it. However I expect you’ll find Tascam use a Sony chipset (CXA and CXD chips) so the design partitioning is probably similar. Tascam probably have their own motherboard microcontroller software though (Sony would never have allowed so many bugs/quirks in my Tascam MD-CD1!).

Not sure what your electronics experience is. I believe the electronics for the spindle motor are fairly simple - spindle speed control is needed but not the same level of servo control as the laser positioning. There is usually a micro control output and a H-bridge driver to the motor. Check the motor continuity and use an oscilloscope on the micro control output on the main board to look for it changing. I realise this does require schematics but a SM for one of the other machines might get you a lot of the info required. 
 

[kgallen]

I've looked at the MD-350 SM I have. The image of the schematic is very poor so I can't see all of the details. But I can see that the spindle motor is indeed driven by channel 4 of a H-bridge driver. From the output to the motor there is a series 100uH inductor and 0R link resistor and a parallel cap (maybe 10uF). The control input to the H-bridge driver comes from the CXD2662R (Sony MD DSP chip). So if there is any chance you can back-trace your unit and find something similar, I'd check the continuity of the L and R. If you have a 'scope then pins 93 and 94 of the CXD are the spindle "reverse" and "forward" drive outputs - you should expect to see pulses on these at probably 0V/3V3 logic levels.

[kgallen]

Funnily enough I’ve now got myself an MD-801R to play with too that is in need of some attention (to say the least!). Schematics seem hard to come by but if anyone happens to have a set... failing that any details on the VFD DC-DC converter - is it negative output and what voltage? (Options are probably -17V or -30V).

Thanks!

[blixabloxa]

tascam_md-801r_md-801p_mkii_mk2_sm.pdf

Here is the service manual.

Cheers,

Enzo

[NGY]

13 minutes ago, blixabloxa said:

Here is the service manual.

I guess this is the same one that is also on Elektrotanya. Sadly it does not have any circuit diagrams, only (rather poor quality) PCB layouts.

 

1 hour ago, kgallen said:

any details on the VFD DC-DC converter - is it negative output and what voltage? (Options are probably -17V or -30V).

Probably -30V. But the VFD should work with -17V as well, only somewhat dimmer.

I am not sure that this SM is 100% consistent, because parts numbering seems different on the PCB layouts and in the parts list. Nevertheless, if the VFD driver IC is what we see in the SM, then its datasheet talks about -35V (actually anything down to -40V).

[kgallen]

Hi chaps,

Thank you both for your quick responses. Thanks @blixabloxa for the manual link. I do have the SM from Elektrotanya, but I will compare the one you provided as often there are several versions in circulation with different information or quality of pictures etc. So thanks! Schematics would be the key!

@NGY thanks for your insightful investigation into the VFD, much appreciated! My MD-801R was bought "spares-probably-not-repairs" (I added that last bit!) just to have a play about with. It has been used as a donor deck to repair another (presumably), so is missing some parts, like this DC-DC converter (in general it's not in too bad shape). As we've seen, there are no schematics although at least a parts list which states U503 as a DC-DC. However there are no other specs or pinouts. Through tracing the PCB, I've worked out the pinout (for anyone that cares, assume you're looking down at a DIP8, then pin1=out, pin4=in, pin8=0V). The input is from the raw rectified/smoothed DC supply and I measured at 16.7V. The output of the DC-DC has a smoothing cap but it's in reverse polarity (cap+ to 0V rail, cap- to DC-DC output), hence concluding the output was probably negative. I found a Facebook repair post on this component. Not many details but one photo was annotated with "29V". Hence my two proposals of 17V and 30V and the likelyhood these supplies were negative with respect to the 0V rail. I've ordered a range of small DC-DC modules - both Boost types (thinking +17V -> +30V) and also some Buck-Boost inverter modules, so I can do both +17V to -24V and +17V to -17V (at least). So the info on brightness for -15V through -30V, and the datasheet picture you found is much appreciated. I did not want to blow up the VFD on the first attempt!

I suspect this machine will still be a little poorly, but getting the VFD working will be a step forward in diagnosing the next fault. At the moment it will accept a disc, but does not spin it up and hence not read the TOC. So once the VFD is working I can take a look at the drive behaviour.

Onwards, fellow MD-ers!

Cheers,

Kevin

[kgallen]

Well with an eBay-special voltage inverter (17V in to -24V out, -30V would be better as @NGY says) the display and main processor are alive!

However it won’t read discs - me thinks this OP looks suspiciously like it’s missing at least one important bit...

 

Next question is do I fork out another 45 quid for a KMS-190A OP or do I declare this project-for-fun null and void?...