This guide shows how to replace the flat cable for the Display Board that connects to the Assigner using modern IDC connectors. It is a difficult repair because it involves removal of the connector on the Assigner Board that has a plated through two sided PCB.
The Switch to Display Board flat cable can be replaced at the same time if wanted, see here for full details.
The cartridge cable is vulnerable to damage in the JX10 design, a guide here shows how it is replaced using PCBs to transition the signals suitable for passing over an IDC connector system.
It is essential that ESD precautions are taken when handling circuit boards and ground the metalwork of the instrument to earth during disassembly & reassembly. An ESD kit (like this one) can be purchased at low cost from eBay.
When handling the Assigner Board, it must be noted that it has a Roland custom Gate Array IC that can be damaged by static electricity and is irreplaceable without removing one from another instrument. Other ICs can be damaged too but can be replaced by modern equivalents or sourced from UTSource. Finding out which IC is faulty on an Assigner Board is guaranteed to bring headaches – Don’t risk it without getting an ESD kit!
Damaged Flat Cable
The glue used to hold the flat cable conductors can lose it’s bond strength with age. Sometimes when removing a flat cable, for example from the display and switch boards, they can get stressed and result in the horrifying condition as shown below. Reinsertion with bent pins would damage the assigner, display and switch board and probably short circuit the power supply.
With a great deal of care, it can be remedied with a more robust solution IDC cable and box headers.
- 2 off, Right Angle 34 Way box header: Farnell 221-5298
- 2 off, 34 Way IDC Socket with Strain Relief: Farnell 221-5256
- Ribbon Cable 34 Way 290mm Long: Farnell 297-355 for 1m
- 100uF 25v Electrolytic capacitor
- Solder Braid for pad clean up
New Flat Cable
The new flat cable is made up from insulation displacement cable and connectors “IDC”, 290mm long, 34 Way, 28 AWG, 0.072 mm² cable, connector pin spacing 0.1″.
The connectors can be attached by squeezing in a vice after carefully lining up the wires with the pairs of prongs that penetrate the insulation and grip the wire.
Before one strain relief clip is applied, the cable has the following properties:
- 290mm long, 34 Way
- Red stripe at opposite end of “V” marked on connectors
- Bump polarisers facing outwards
- When laid flat, one connector faces up and one connector faces down
The details of the cable and what it looks like is shown in the picture below.
The cable has a strain relief at the end that plugs into the assigner, the strain relief cannot be fitted in the Display Board end because it would otherwise foul the rear of the lid when installed.
Special note, the original cable is 290mm long. With the new method, it needs to be between 240mm and 290mm, up to 50mm can be removed such that it doesn’t have to be folded like the original. These instructions and pictures show a 290mm cable.
New Flat Cable Testing
The Flat cable has to be tested, otherwise serious damage to the assigner, power supply and display boards can occur if shorts are present.
Connect the cable to the IDC headers that are not yet fitted to the boards and use them to check the following:
- Continuity between cable ends
- Confirm no continuity between each pin and its neighboring pins
If IDC cables are not made properly, they can short adjacent signals or not connect at all. Once made, it is not recommended to take them apart and remake them. It is a good idea to order spare connectors in case mistakes are made.
The picture below shows a cable being tested using a multi-meter on “continuity” range using spare right angle and straight pin headers.
Do not attempt to poke test probes into the IDC connector cable sockets, otherwise the contacts inside will be widened and lead to intermittent connections when installed.
Remove Display Board Connector
Using a desolder pump, remove the existing flat cable header and 100uF capacitor C1 on the Display Board. Note that these pictures show a Display Board where the original Vacuum Fluorescent Display has been replaced and upgraded.
Capacitor C1 is not required if the display has been upgraded and can be discarded. If the original display is still present, then the capacitor needs to be replaced with a new one with longer leads as the old one won’t reach with the new connector in place.
It is necessary to clean up excess solder so that when the new connector is fitted, the pins don’t foul the excess solder and damage the copper pads on the PCB. The best way to do this is to use “solder braid” and a little extra flux.
The new connector has to be glued in place because the PCB doesn’t have double side plated through holes and is therefore very weak. Use IPA to thoroughly clean the area where the new connector is going to sit.
Fit Display Board Connector
The new connector has double row pins rather than “alternate” like the original connector. The new connector is fitted under tension because the back row of pins are at an angle. This requires patience and care not to bend any pins out of shape.
The best way of fitting is to push the rear pins in the first row of holes (on left in picture below), then using sideways force as shown by the green arrow, align the front row pins into the second row of holes before pushing them into place.
Once in place with the connector fully pushed down, tilt the connector back slightly in order to gain enough room to apply glue but not let it fall out.
Apply superglue in three places, ideally where the protrusions are that rest on the PCB surface.
Solder the connector pins to the board whilst ensuring the connector is flat to the PCB. This can be achieved by soldering a pin at each end, then reheating the joints, followed by pinching the PCB and connector together whilst the joint cools again. This ensures that any forces applied when fitting the new cable don’t lift the connector pads off the PCB.
Fit the replacement 100uF 25V capacitor if the Display Board has the original display.
Fit Assigner Board Connector
The Assigner Board connector is best done after gaining practice on the Display Board. Removing the connector without damaging the plated through holes on the PCB is difficult.
Using a desoldering tool, remove the solder off each pin. Here are some hints and tips to achieve the best result:
- Try to optimise the heating time to get the best result without “cooking” the PCB otherwise traces will lift off. Pads reaching wide traces, e.g. power and ground, will require a little more heating time.
- If not all solder is removed, reapply solder to the joint and try again.
- Once the joint has cooled down, place the tip of the iron on the pin itself to move it away from the edge of the hole. A satisfying “click” will be heard as it disengages from the remaining solder in the hole.
- Check that the pins are loose in their holes, if not then reapply solder and try again.
Remove the connector very carefully, it should be loose at this point and whilst moving it gently from side to side, the pins should all move together. Pins that don’t move still have solder attaching them to the wall of the through plating. Touching the iron on the pin whilst moving it should allow it to break free.
After the connector has been removed, touch up each pad by applying the iron to each pad in turn. This will melt any remaining solder in the plated through hole and smooth the surface ready for the new connector.
Inspect the through hole plating by holding the PCB up to a light, also inspect the pads and traces around the holes on both top and bottom sides. In the picture below, some damage to a ground trace was found where the pad was partially torn away when the connector was removed. This was later replaced using a wire link once the new connector was installed.
Fit the new connector using exactly the same method as on the Display Board taking care not to scratch the top surface traces with the connector pins. There is no need to use superglue because the double side pads with plated through holes are very robust once soldered.
Looking very closely at the top side pins after soldering should reveal a “fillet” around each leg indicating that a good joint has been made to both top and bottom side. If looking carefully, it can be seen that the picture shows an “incomplete fillet” around the torn pad pointed out earlier. Make any necessary repairs to traces that were damaged during connector removal.
The cable end without the strain relief is fitted and routed to the display board as shown in the pictures below.
Once the Display Board and Assigner Board have been refitted, insert the assigner cable end with the strain relief is fitted as shown in the picture below.
The final installation with a full set of flat cables for Display, Switch & Cartridge. Note how the Display Assigner cable is folded just like the original, although made to the original length of 290mm, it could have easily been 240mm, 50mm shorter!
The beauty of this installation now is that the instrument can be moved without fear of vital signals being intermittent.
Copyright © 2018 Super Synth Projects, Guy Wilkinson