NOT FOR PUBLIC DISPLAY

Technician Notes
Product: AD-8000
Topic: General Technician Notes
Document #: 6


Mechanical
1. Short front line screws: On older units (identifiable by the lack of screw holes lining the back edge on the top cover), the screws on the top and bottom cover that line the front panel are shorter than the rest. Make sure that the long screws do not go in these holes because they will drill a hole in the front panel PCB cutting a trace that is very close to the edge of the PCB. The symptom that will be displayed on the front panel when this occurs is that some of the segments will be missing on the seven-segment over indicators. To fix this, scrape a small portion of the trace that is just under the screwhole on either side of the hole, then jumper across to re-connect the trace.
2. DAC-8 Installation: Installation of the older serial number DAC-8 cards requires some caution. Push back the ribbon cable/connector that connects the power supply to the analog board so that the edge of the DAC-8 slides down just in front of the connector. If you push down without sliding the ribbon cable connector back, you can potentially damage the connector. The later DAC-8s have this corner cut at a 45 degree angle to fix this problem.
3. AMBus A slot fit: If an AMBus card doesn’t seem to slide all the way back into slot A, the L-bracket that holds the AMBus card back panel to the PCB is probably bumping up against the chassis. The only way to fix this is to shave down the top of the "L" bracket about 2mm with a file or a filing machine.
4. AMBus D slot fit: Sometimes an AMBus card will not go in all the way into the bottom slot (AMBus D). This is because the legs of the through-hole chips on the underside of AMBus PCB bump into the chassis. If these are too long cut down the points on the underside of the AMBus PCB.
5. Pinched cables: Make sure, when removing and reinstalling any PCB (analog, digital, and power supply), that no cables are pinched on the underside. This will cause a series of failures. This includes the black & white power cables that lead to the A/C receptacle; the headphone cable; the cables that lead under the digital board to the power switch. Also, make sure that the A/C cables are flat against the chassis. If not, the metal trough that covers the cables will pinch the cables and the boards won’t fit correctly.
6. Long screws: When working on older units, check to see if all the screws holding down the analog and digital boards are the longer screws (size = 6-32 X 7/16). Replace any of the shorter screws (size = 6-32 X 3/8) that have the locking washers with the longer screws without locking washers.
7. Front panel buttons sticking: There may be a few units that have front panel buttons that "stick" against the plastic silk-screened front panel piece. This is because the front panel holes through which the buttons poke are sometimes slightly too small for the button to easily slide through. To fix this, remove the button in question with a small flat-head screwdriver by carefully pushing the tip of the screwdriver against the side of the button and pulling towards you – one side and then the other (gently) until the cap of the button is removed entirely. Then, scrape the sides of the hole of the silk-screened front panel to make the opening just a very small bit wider. Do not cut into the plastic – only scrape with the side of the blade. Usually only a small amount (2-3 scrapes) is needed to open the hole just an infinitesimal amount. Re-install the button and test.
8. DAC Card Chassis Grounding: On every unit, check the two top screwholes where the DAC cards screw in. On the inside of the back panel, where the DAC card makes contact with the chassis, the paint on the chassis should be scraped off so that the metal of the DAC card and the metal of the chassis can make good contact and share chassis ground.
9. Headphone output: If one side of the headphone output does not work, consult ECN #61. Compare the resistance of one channel to the other. Re-flow solder if there are any cold solder joints. Also, sometimes the left and right sides may be reversed. We usually catch this sort of problem at Apogee. If you find one like this, switch the leads at the headphone connector. If both channels are not working and you’ve checked the connector, there is a possibility that the DAC chip has failed (U1 bottom right corner on the analog board) or the amplifier chip has blown (U2 in the same vicinity). Turn on the AD-8000’s oscillator and check for data input to the DAC at pin 5 and check for analog output at pins 9 (right) and 12 (left). If this is OK check for input into the amplifier chip (U2) at pins 6 and 9 and then check for amplified output at pins 2 and 13 of U2. If the DAC output is OK but you’re not getting input into the amplifier chip then there is most likely a cold solder joint in the rework in between the two stages. With your finger, move the caps and other components just to the left of U2. Check for cold-solder joints and re-flow solder as needed.
10. Intermittent behavior at the analog inputs: Check for cold solder joints at the resistor networks (RN1 and RN2). Measure resistance across opposite pins and compare it with a good channel. See Tech Note #6 AD8K Analog PCB Troubleshooting for more information.
11. Standoffs under Video Sync Module: The early version standoffs that fit under the Video Sync Module are too tall. If you come across this, remove the standoffs and replace with the normal mounting screws (just like the screws that fasten the analog and digital PCBs). Also, the first version of the Video Sync Module had holes that did not line up with the standoffs. Securing the VSM to the standoffs is not necessary. The connector holds the VSM securely without the use of mounting screws. When re-installing the Video Sync Module, make sure that all the pins line up with the correct holes. If you see that the Sync Source will not go down to the pull-up and pull-down rates, check that the VSM is inserted correctly.

PSU
The following points are not valid with Rev E power supplies. In most cases, you will simply exchange the installed power supply for a Rev E PSU if the unit does not already have one. The Rev E PSU has a taller transformer and is generally bigger in size than any of its predecessors. It is somewhat difficult to install as it just fits in the space provided (see Tech Note #1 AD8K Rev E PSU Installation). Also, older chassis units must have extension stand-offs installed on the existing chassis standoffs before installing the new revision PSU.

12. Transformer Revs: The connector of the transformers differ from rev to rev. The earlier transformers (rev A and B) have two rows of five points, the later ones (rev C and C2) have three rows. The very latest rev (E) will have two different connectors and will look nothing like the earlier power supplies.
13. Black transformers: If you push lightly on the center section of some of the black-covered transformers, the center section pops out. Do not use these transformers. If you come across one of these, replace it with the normal silver covered transformer.
14. Mylar ring: Underneath the transformer there should be a rubber ring, then a Mylar ring between the rubber ring and the PCB. This is used to prevent arching from the transformer to the PCB that causes the rubber ring to burn and also causes damage to the power supply PCB.
15. 220 Power Supply: For a unit that will be used at 220V or above, make sure that the rectifiers on the heat sink are "S6" as opposed to "S4" (S4 can only be used on units operating at 120V and under). Manufacturer part # D4SB "S4" and "S6".
16. Fan switch: The size and position of the vent holes on the side of the chassis vary with the serial number. The later serial number units have larger vent holes; in fact, there are three versions with vent holes of different size and position. This is important when installing the new power supply. If the power supply that is being installed has a power switch for the fan, the switch must fit through one of the vent holes in order to be switched on and off. On the earliest chassis, the fan switch is positioned correctly without the use of a standoff. On the second version, a standoff must be used in order to get the switch to line up with the hole. In the third version, no standoff is needed.

Symptoms
1. Motor boat sound/fluttering/popping: When the jumpers on the DAC-8 card are configured for balanced operation and the outputs are fed to an unbalanced source, one of the signal pins will be grounded out and there will be loud noise at the outputs. Have the customer change the jumper configuration on the DAC card so that the first four channels reflect the four possibilities: unbalanced +4, unbalanced –10, balanced +4, balanced –10. Listen to each channel individually to determine the quietest one and set all the other jumpers to match the quiet one (see App Note #1 AD8K DAC 8 Noise).
2. Noise on the analog inputs: This will often have to do with a grounding incompatibility. Have the customer remove (or install) the jumpers on the analog board (JP1-1 to JP1-8) and listen to determine the best setting.
3. Burned ADC chips: If the A/D converters cannot be calibrated correctly or there is attenuation of the signal or excessive noise, check the ADC chips (U27-1 to U27-4) to see if they are brown in color. If this is the case, the ADC chips are burned and must be replaced. See Tech Note #6 AD8K Analog PCB Troubleshooting.
4. Heat: This is the number one enemy of this product. If customers call complaining that the unit gets progressively worse, ask them if they have any ventilation to the unit. Have them turn off the unit for an hour and see if it improves. If it does, then they must provide more ventilation and cooling to the unit by either turning on the power supply fan or removing the unit from a rack. The new Rev E PSU stays much cooler than older revisions PSUs. It also works better at the international voltages of 100/220/240V/50Hz.

Applications
1. Outputting to the same input source: With EPROM version 1.15, the AD-8000 mutes the output to the source that is selected in SOURCE SELECT. Apogee changed this in EPROM v. 119. Output to the INPUT SOURCE device is now active.
2. Error light when using with sampler: Some samplers do not send the correct S/PDIF validity bit. With EPROM v. 115, the AD-8000 will light the Error LED and mute the output if it does not see the correct S/PDIF validity bit. To troubleshoot this, have the customer connect another S/PDIF signal (such as a DAT player) to the AD-8000 to see if it works correctly. EPROM v. 119 ignores the validity bit and passes audio through regardless of the status of this bit.
3. Synchronizing multiple AD-8000’s: When synchronizing more than one AD-8000 (and other equipment) to a master source, such as a master AD-8000 or video sync generator, connect each successive AD-8000 using a BNC T-splitter. This is a better method of synching multiple AD-8000s than using the WC input and the WC output. For a complete diagram, see App Note #12 AD8K Pro Tools Configurations.
4. Non-volatile memory: There seem to be some configurations that are not remembered by the AD-8000 correctly. These involve configurations that have digital inputs. This may have to do with the power-up sequence. If the AD-8000 is clocking to another device and that device is turned-off before the AD-8000 is turned off, the AD-8000 will go into an ERROR condition. Upon re-powering the AD-8000, it will not remember the ERROR state but will boot to the default setup. There are other configurations with version EPROM v. 1.15 that are also not remembered. As of Jan 25, 1999, there is a new revision EPROM v. 1.19 that fixes this non-volatile memory problem.
5. ADAT/BRC synchronization: There have been several instances where the AD-8000 and the BRC have not synchronized correctly. The symptoms are that, when the BRC is WC master, the 44.1 and 48 sync LED’s on the AD-8000 alternately blink (this indicates that the AD-8000 is not receiving exactly 44.1K or 48K). When the AD-8000 is WC master to the BRC, there are audible pops and snaps. In every case, switching out the BRC has fixed the problem. Defective BRC’s should be sent to an Alesis service center to be repaired.
6. Digi-8 card channel swapping: Some of the very early Digi-8 cards swapped the channels pairs at random (1 goes to 2 and 2 goes to 1). This problem can only be remedied by changing the Digi-8 card with a Digi-8+ card.
7. Out of phase DAC-8 cables: If the output signal of a DAC-8 card is out of phase, make sure that the 25 pin output cable is pin 2 hot (the AD-8000 assumes that the cable is configured for pin 2 hot). There have been instances when a studio has set up the DAC-8 for pin 3 hot operation but had a pin 3 hot multi-pin cable; thus, the signal was out of phase. The Tascam specification calls for the cable to be pin-2 hot.
8. Error correction: When CDs are badly scratched, some CD players will put out an invalid data bit from their digital outputs. If the AD-8000 sees an invalid data bit, it mutes the audio. The tricky thing is that the CD player’s own DACs may ignore the invalid bit and still pass audio. So that, in this case, you will hear audio from the CD player’s analog outputs but not from the AD-8000. EPROM v. 119 ignores this invalid bit and passes audio normally.
9. Multiple digital inputs: This question pops up quite often: "Can I feed the AD-8000 multiple digital inputs simultaneously?" The AD-8000 can only accept one digital input source at a time. A "back-door" way of doing this is to put the AD-8000 in destination mode so that the initial digital input is being fed directly to the destination AMBus card. The destination device should have its channels in throughput mode. The returns from the destination device are fed back into the AD-8000 and are output to all the available outputs.
10. Single TDIF and ADAT cards -- which AMBus slot?: When using only one ADAT or TDIF card with the AD-8000, make sure it is installed in either slot "A" or "C". Do not install in the "B" or "D" slot. This has to do with the correct functionality of the bit-splitting function.
11. Checking the EPROM version w/o opening the top cover: When powering-up the AD-8000, press and hold the SOFT LIMIT button. On the 7-segment displays will appear the installed EPROM version. It will say, for example "CODE 115". Then it will display a checksum and boot to its normal state.
12. By-passing the boot-up wave for faster boot-up: When powering-up the AD-8000, press and hold the CLEAR METERS button. This will by-pass the initial boot-up razzle-dazzle.