Roland SDE1000 repair guidance needed! - Page 1
Forum section: electronics / repair

author: trondl
author_rank: Regular Contributor
timestamp: January 18, 2021, 06:53:22 pm
content: First post here, and sorry for the length. I didn't want to leave too much out.If you are willing to read this post: Thank you for your time!TL:DR? Go to the last section please!I have a Craft Certificate in electronics but I have never worked in the field, so my knowledge is limited.Don't trust my logic or measurements!Service manual found here:https://www.synthxl.com/wp-content/uploads/2019/07/Roland-SDE-1000-service-notes.pdfPlease jump directly to page 17 for the schematics.This is by far the most complicated troubleshooting in my hobbyist career.Equipment I've used so far is a Siglent 200MHz 2ch DSOscope, a Siglent 5MHz sig-gen, a not the cheapest but certainly not a Fluke DMM, and a Minipro TL866+For all sig-gen testing I've used a 1KHz 0.22 VPP sine on the units input.Long story short:I got this Roland SDE1000 mono delay audio effects from 1984 about 5 years ago.When I got it, it powered up and ran for about a minute or two.It then started all of a sudden to glitch out, displaying garbage in the VFD display and the audio that was still active in the RAM was looping and starting to distort.No further audio input was being processed.The unit was then immediately powered off for a quick smell and visual inspection.No magic smoke or heat was found.I let it cool off for an hour and it then started up again, but this time for a couple of seconds before glitching.Later it would only start up again when the unit itself was cooled down to way below room temperature.My logic back then was: recap psu and change rectifier bridges.This didn't change much, except that now the display would either be "8.8.8.8." or "....", when it should be displaying the delay time in milliseconds, as in sitting idle or frozen.I wasn't that good at meassuring ripple and finding all the rails and such but the +15- -15 +5 and +12 looked OK.+15 and -15 transistors are a pair of 2SA968/2SA2238 that runs hot, but not scorching hot.Apart from them, no component run suspiciously hot.Now I'm a bit wiser as this is the last unit in my "too hard to fix yet" pile.Ripple on the +5V, -15 and +12 has very little ripple after the psu overhaul, but the +15 rail has about 0.5 - 0.6V ripple.More on this later!VDD is 5V and VCC is 4.88VAt first I was focused on the digital domain (maybe a bit too much, more later).I was first suspecting reset and generation of both the clocks to the main controller IC12 and CPU/co-processor IC21.Reset circuit was doing as it should do.CPU (IC21, a custom 80C49)The 11MHz sine was measured on the X2 pin swinging steady between +1V to 3.9V without refference to ground on my probe, and 0.8V to 4V with reference to chassis ground.Yes, this unit has a mains ground plug, and is being used.I'm still a bit confused about when the ground lug should be used, but I've learned to be sceptical about using it.All the P(nn) and DataBus pins have little (mV noise?) to no activity.The P(nn) ports which where inputs from the foot controller jacks on the back of the unit where tested with a foot switch and all had the correct responses on the CPU inputs.T1 input from Main Controller (IC12) is correct with a clean 40 to 44Hz 5v pulse that correspond with the position of the Delay Time X1-X1.5 potmeter position.My biggest fear here is that the CPU is toast as it has a custom PROM on it.I did out of curiosity meassure the ALE pin, and there is steady activity there.Could this mean that the CPU is most likely OK?If you jump to page 9 in the SM you see a CPU Modes section in the middle.What I've found is that the CPU state is in row 2 on the Normal Mode, which should indicate that the CPU is actually running.Almost all logic chips have been desoldered and verified with the TL866 except the 7407 buffers before the dac.Next is the main controller IC12.MSCK clock input is abit hard to measure with a probe as it either distorts very or has weird ringing on the top and bottomn part with and without reference to chassis ground,But HDCK which is generated from this clock is generated so I believe it to be OK.All the address lines to RAM show healthy activity, although the output from the ram seems like weak digital noise.Since the 1KHz sine arrives healthy at the DAC side later, I believe the output to be OK.Data outputs to the resistor ladder DAC show healthy activity.SAH (Sample and hold) is as expected according to the manual.DATA and SIFT (Shift) has no activity from the CPU IC21. I forgot to log if it was high or low though.Now, I believe I'm onto something:DIN which seems to have a digital pulse going but has a very noisy low phase, as in down to -0.5V switching noise.This signal is according to what I understand the data that is part of the calculation of the delay time which should be written to the VFD.The last discovery was actually made during my attempt to broaden the horizon and focus on the analog domain as my gutfeeling told me there must be a point where the analog meets the digital for preset storage and control.I started to trace backwards at Delay Out IC28 (opamp), and what did I see?After a cold start, the 1kHz signal from the sig-gen would gradually stabilize after 5-7secs, BUT after about 15-20 seconds would slowly become unstable and starting to look like a mayhem taking place, as in full rail noise and then gradually dying out.That is excactly what happened when I first got it!I then traced more backwards and found the same behaviour all the way back to the Comparator IC2 Pin 3, marked as test point 3 in the schematics. Pin 2 has a clean signal.According to the schematics it's a NJM311D but in reality a NEC C271C.This is the very chip that generates the DIN signal to the Main Controller IC21 on pin 7 (D23 is tested ok with DMM)A small step backwards from IC2 pin 3 we have Q10 which shows a healthy sine. Should this indicate that the circuit backwards to the 7404 buffers is ok?7407 has all healthy inputs/outputs.Right next to it we have Q9, an n-channel JFET K30A GR that I believe is the source for everything:A 0,5V ripple/leakage on the +15 rail it sits on and feeds Comparator with noise so the data to DIN on main controller gets garbled, freaking out the controller.Am I onto something here?Could this JFET really cause ripple on the supply? and in worst case, destroy the input DIN on the Main Controller?Stress testing a JFET is a bit out of my grasp.Or is the +15V driver transistor really the culprit?Q43 (K117 GR) marked in the top north-east in the schematics, is often mentioned as being leaky, causing a drift in the delay display time. I haven't thought of it as critical so far as the output looks fine.Is there anything nearby I also should check before I try to find a replacement/equivalent for a K30A GR?If any of you have a large stock of K30A GR and K117 GR and are willing to donate one or two for shipping to Norway, I'm all ears.The nearby IC5 4066 tested OK out of circuit with the TL866.If you made it down here:Again, thanks a bunch for your time!MvhTrond

author: fzabkar
author_rank: Super Contributor
timestamp: January 18, 2021, 10:14:57 pm
content: The 80C49 has a 2K x 8 ROM.https://web.archive.org/web/20201123220508/http://www.bitsavers.org/components/toshiba/_dataBook/1988_Toshiba_TLCS-48_90_8_Bit_Microcontroller.pdfSometimes you can read the ROM even if the chip is not fully functional, and you can then program the EPROM version, 87C49.A "K117 GR" is a 2SK117-GR.A "K30A GR" is a 2SK30A-GR.C271C is a uPC271C:https://www.renesas.com/document/dst/upc271-311-datasheet?language=en

author: nanodocl
author_rank: Contributor
timestamp: January 24, 2021, 10:50:13 am
content: Is the hand writing on the schematic regarding Q43 yours?Regarding K30A GR and K117 GR, there are few good available sources on this jfets you can try this ones:https://www.banzaimusic.com/2SK117.htmlhttps://www.retroamplis.com/epages/62070367.sf/es_ES/?ObjectID=85598992PD: Do not try ebay or aliexpress for this jfets, most or them does not work or they may make the fault even worse.

author: trondl
author_rank: Regular Contributor
timestamp: January 24, 2021, 03:10:18 pm
content: I think I may have found the real problem: ic13 7406 o.c. Hex inverter fails to go high on two outputs when the reset/mute circuit goes low after initializing. This holds P10&11 on cpu low so it cannot read the front panel switches etc.Ic 26 4049 which is in front of ic13 inverts corectly.Ic 13 has two inputs floating, and it has weird voltages on the input two inputs (1.2V or close).Two other inverter ports are used on the comparator, and seem to work correctly with lots of trafic.Out of circuit, ic13 is tested ok by tll866.So ic13 has two working gates, to floating, and two that always output low.Should I tie the two floating inputs to ground, or pullup to high?Part number is HD7406PThanks in advance

author: trondl
author_rank: Regular Contributor
timestamp: January 24, 2021, 04:43:13 pm
content: nanodocl: the handwriting is not mine. It’s the only manual in circulation i guess.

author: Renate
author_rank: Super Contributor
timestamp: January 29, 2021, 12:41:10 pm
content: IC 13, pins 2, 4 is a "mute" on the input panel.It should normally read low (but not driven low by IC 13).Push some buttons on the panel and you should see some positive pulses from the keyboard scanning.That is, you should see that if IC 20 is scanning, check for action on pins 11-18.If you're still having reset based problems, check the voltage on the 4 electrolytics in the reset section.In normal running all 4 caps should be at their resistor supply voltage (+5 or +15).Some of the pullups are awfully high (470k, 560k) for crappy old electrolytics.I really prefer not pulling any components for testing until I'm dead sure that it's bad.Even if I do a good job removing things the chance of complicating everything is too high.

author: trondl
author_rank: Regular Contributor
timestamp: March 30, 2021, 02:45:01 pm
content: Thanks for the knowledge!Almost all the caps have been replaced except those bellow 10uF as I don’t have them in stock.I am also starting to believe the reset circuit is misbehaving, possibly releasing the line too quick before the clock or 5V has stabilized.Since ALE on the CPU is showing a pulse, it should be executing although not properly reset.Is there a quick way to manually reset the cpu after power on?Short reset pin to ground for a second? Or would that cause trouble for the reset circuit itself?Temporarily solder in a switch somewhere in the circuit?I get that the reset circuit is RC based, but I don’t understand where they are in the circuit.

author: Renate
author_rank: Super Contributor
timestamp: March 30, 2021, 03:12:24 pm
content: Did you look for action on IC 20?Did you check the voltages on the 4 reset caps?The upper right should be zero, the other three should be about 5 V.IC 22 should be high on pin 2, low on pin 4 & pin 6

author: trondl
author_rank: Regular Contributor
timestamp: March 30, 2021, 03:24:17 pm
content: Renate: I haven’t checked yet due to time.They’re the first things I will check.I do remember checking if the buttons pulse did arrive back to the CPU, and they all did.Upper half at one pin, and lower on the other.In the mean time I thought about how to reset the CPU manually to verify if this is actually a reset issue or if it is something more sinister (PROM bitrot).

author: trondl
author_rank: Regular Contributor
timestamp: March 30, 2021, 03:27:20 pm
content: Renate: also, Thanks for pointing out the relevant caps!I’ve only replaced the 22uF.

author: trondl
author_rank: Regular Contributor
timestamp: April 08, 2021, 07:52:51 pm
content: Renate: Measurements have been made!IC20: No activity. Some high, some low.IC19 and IC20 have previously been swapped to check for changes. Same result.Button switch pulses arrive via pin headers 15 & 17 back to CPU P10 & P11IC22 seems to be ok: pin 2 high, pin 4 & 6 lowPoR/M circuit:C72 +4.26V Ramps up very slow, more than a secondR190 +4.26VC73 +5.9V Has been recapedR175 +14.8VC67 +0.25V Rising sawtoothR156 +4.9VC68 +1.9VR159 +4.9VPoR/M timingReset ~250msClk ~160msVCC ~25msVDD ~155msCPU ALE ~155ms Has about 0.7kHz pulse, indicating it should in theory execute code.The only logic close to the CPU not verified by the TLL866 is IC18 (74LS48N bcd decoder).I have tried grounding the Lamp Test pin, and all segments worked.Since CPU DB6 controls the .dot in the display, and the only thing displayed is ". . . .", unless the unit has warmed up for about 30m-1h, it may then starts to display a number which shifts/cycles left after a quick power reset.Could IC18 force the bus stuck? and could it be removed from the circuit to check if the CPU awakens?Sometimes when probing the Reset and/or the Clock, the CPU glitches and all the button LEDs and segments in VFD turns on.Also, maybe the clock crystal is a bit weak?Definitely not 0-5v, more like 0,8v - 4v at best.I do have a 2 pin 11Mhz crystal resonator at hand:https://uk.farnell.com/iqd-frequency-products/lfxtal003327/crystal-11mhz/dp/9712399Could it replace the 4 pin oscillator?Additional idle CPU data:T0 5vT1 40-44hz square ~5vP-PP20 5vP21 5vP23 5vP10 0vP11 0vP12 0vP13 0vP14 0vP15 0vP16 5vP24-27 3.7v to VFD. Ramps up to 3.25v, then after 155ms jumps to 3.7vDB7 3.2vDB6 3.2vDB4-5 0v a bit noisyDB0-3 1.2v

author: Renate
author_rank: Super Contributor
timestamp: April 08, 2021, 10:12:57 pm
content: Wow, lots of info there. I'll have to look through it well.I'm thinking that the first diagnosis was the correct one, that the CPU PROM is going.I think that I'd concentrate on reading out the data even if it turns out to be another problem.Apparently it's easy.12V to EAReset LowAssert 12 lines addressReset HighRead data off 8 of those 12 linesAn Arduino should be able to do that easily.The only non 5V logic signal is the EA which is just a constant 12V.In any case, you'll sleep better knowing you have the data.OTOH, this is masked? not regular PROM, how can it degenerate?In ye olde day we used to have cans of "Freeze Mist" (those lovely CFCs) and there were lots of thermal problems with things.I'd put the unit in a freezer and see if it will work normally for even a minute.

author: trondl
author_rank: Regular Contributor
timestamp: April 09, 2021, 06:58:35 am
content: As I feared, and after verifying a somewhat healthy PoR sequence, I'm starting to believe so too.Considering that the unitinitiallyresponded to cold temperatures, I'll check if it can be brought back again.It's about 3 degrees Celcius outside now. I'll give it a bit of fresh air.Yes, it's a masked PROM if I understand it correctly. Wikipedia: "The 8049 has 2 KB of masked ROM"Just to be sure, I cannot dump it _in circuit_, no? Desoldering it is no problem.I have seen Arduino circuits constructed to dump MCS48 PROMs that did look a bit complex, involving transistors.Also, the TLL866 should also be able to dump it with some support circuit?If I'm able to dump it, luckily a 87C49 is not that expensive, or even better, the CPU is ok but needs it's ROM externally.

author: trondl
author_rank: Regular Contributor
timestamp: April 09, 2021, 08:05:04 am
content: Partial Success!!!I brought the unit to about freezing temperature outside.It was initially glitching, but a power cycle later, it came back to life.All logic and switches working as it should.This lasted for about two minutes before it froze (pun intended?).I let it cool down for a few seconds, and the same results.I tried editing it and save the presets, which worked.Now that I've brought back inside, it's all dead again.One thing I noticed before freezing (Random values in the VFD):The value started to jump to about double the initial value, and then drifted both ways a bit.There is a BIG hint in this: As mentioned in the hand writing in the Delay Time schematics (upper middle), Q43 (2SK117 MOSFET) is known to turn leaky and I think it is responsible for the delay calculation.Although this only report back to the main controller, could this be as simple as an itchy MOSFET?Should I try to swap it with a less mission critical transistor in the circuit?Since I can somewhat reliably bring it back to life, is there a special area I should pay extra attention to when probing for the actual offender?I do have a "Dust Off" can that does generate some condensation but does have a cooling effect. Worth a try?

author: Renate
author_rank: Super Contributor
timestamp: April 09, 2021, 11:01:38 am
content: Quote from: trondl on April 09, 2021, 08:05:04 amYou mean if you hold it upside-down and liquid comes out?Sure, I'd certainly try it.

author: trondl
author_rank: Regular Contributor
timestamp: April 09, 2021, 11:52:10 am
content: I tried to freeze Q43 first, no change.Freezing the CPU though worked.I waited until it crashed to measure the temperature with a cheap IR thermo, and it was around 12degC.The rest of the circuit was close to room temperatureProblem is that the clock crystal is veeery close by, so I cannot exclude it entirely.As mentioned, I do have a 2 pin 11mHz crystal resonatorI could put an ice cube in a sealed plastic bag on top of the CPU or crystal osc?

author: Renate
author_rank: Super Contributor
timestamp: April 09, 2021, 12:50:45 pm
content: If it's really the xtal, a scope probe on one of the terminals should make it either better or worse.In any case you'll see what it's doing with the extra capacitance.I'd try a nice hunk of metal in the freezer.That would be a better surface for conduction.Maybe put a few drops of IPA on top of the chip before laying the piece of metal down?Is it time to order that tank of liquid nitrogen yet?

author: trondl
author_rank: Regular Contributor
timestamp: April 09, 2021, 03:41:17 pm
content: Looks like a liquid cooled CPU is needed.Now that would be a worlds first on an MCS48A big bolt from the freezer with IPA on the CPU did the trick.I managed to probe some around and saw tons of activity on the bus for the first time.Now on to dump the ROM.You mentioned an easy Arduino hack.Was it this project?https://www.eevblog.com/forum/microcontrollers/simple-programmer-for-vintage-intel-mcs-48-microcontroller/

author: Renate
author_rank: Super Contributor
timestamp: April 09, 2021, 05:23:47 pm
content: I'm getting all confused now.The manual that @fzabkar linked shows only masked PROMs.It has waveforms for reading out the PROM using EA at 12V.Page 69 has absolute maximum of EA of 13V.A random project I saw documented just reading out the values of a masked PROM.I'd certainly first try to read this with something with no higher voltage programming supply.I'd be very careful about using the right EA voltage too.The thread that you linked speaks of 6V.