Factory procedure on servicing
Optimod Fm 8100A/1

8100A1 with face plate open at the lab bench.

How to change Pre-Emphasis circuit parts on Card #6 from US & Japan Standards 75ms/sec to European Standards 50ms/sec. Procedure   Here



Hello serious fan or sound engineers of Optimods around the globe. Here is the promising info on how to keep healthy your 8100A1/XT or XT2 Including the latest updates directly from the factory guidance, released just before the digital Optimod 8200V1.0 comes out. Must do all the following steps which is suggested from the factory for a good working order.

Servicing the 8100A And 8100A/1 Procedure Directions.
Rev 1998

PS: If anyone has any other interest info on servicing, upgrades modifications etc gladly I added here, will be useful for all of us:-) Also if notice any error or misspellings please let me know.

Email 261fm(at)261.gr

Thank you

Servicing the 8100A & 8100A/1

 1) Plug unit in a listen to it.

2) Open unit up. Remove and inspect all cards.

3) Unmodify and update cards including any field updates.

4) Install any RET kits
(RET27 and 8100AFC card # 0 are the most common).

5) Realign cards in this order
(See section E in the owner’s manual).

a) Power supply

b) Card #3

c) Card #4

d) Card #5

e) Card #8

f) Card #9

g) Card #0

h) Balance left and right channels

i) Card #6

j) Card #7

k) Do full test and alignment on unit.

6) Perform Field Audio-of Performance Procedure in section D of the manual.

7) Test interfacing unit with a XT or XT2 chassis.

Servicing the 8100A/XT and 8100A/XT2
1) Must have a properly aligned 8100A/l to service any 8100A/XT or 8100A/XT2. 

2) Set the jumpers on Card #5, Card #6, Card #8 and Card #9 for XT2 configuration.

 3) Verify that the 8100A/1 has the correct #5 card. Verify that any modification needed have been done.

 4) Verify all upgrades are installed in the unit. There are three updates, Upgrade #l, Upgrade #2 (RET-36) and Upgrade #3 (RET-39).

 5) Perform Field Alignment starting on Page 4-9 of the owner's manual.

 5) After alignment do field audit of performance on page 4-2. 1 Version 1.0 (October 9, 1997) 8100A/1 Cards Initial Checks and Updates

 Power Supply
1) Make sure the ground link on the rear barrier strip is installed.

 2) If this is an 8100A/1, it should have RET-27 incorporated into the chassis.Resistors R103 and R104 on the regulator board should be 0.62 ohm Resistors and the DB25 connector should be wired to the mother board. Older units, the 8100A's and some 8100A/1's used 0.91 ohm resistors. In This configuration an attached XT or XT2 chassis will not run correctly because not enough current is available. Regardless of what version the 8100 is, replace R103 and R104 with 0.62 ohm resistors.

 3) If one or both of the power supply rails read higher than ±15 Volts and is not Adjustable, then the regulator circuit has gone bad and the only thing preventing the power supply rails from going to 23 volts are the zener diodes VR101 and VR102. Note, coloration around the zener diodes, i.e. black Charred marks on the board are a dead give away of a regulator failure. If this happens, repairs the regulator circuit and then replaced VR101 and VR102.

 4) Change power supply capacitors C111 and C112 if they are the orange type with 47uF, 100V electrolytic.

 Card #3 & #4
1) Undo any modifications the customer has done to the card.

 2) Note: Only on older PCB versions.
Install PCB modification at IC310 to prevent oscillations of the op-amp, Connect Pin 6 & 7 of IC310 together. Connect Pin 3 & 5 together.

 3) Replace the input potentiometer if it is the old aluminum type. The old ones tend to split and cause problems.

 4) If input potentiometer is feels stiff when turned, clean with solvent (TMS FREON spray works well).

 5) Replace the power supply capacitors C327 and C328 if they are the orange Type. If your unit has these capacitors, the unit is really old, plus the orange Ones tend to dry out and cause problems. Replace with 100uF, 25V electrolytic.

 Alignment Procedure Notes:
1) If unable to achieve a C`MMR better then -70 dB (typically < -75 dB) look at the waveform on the oscilloscope. If the wave form looks dirty or there is 'pop-corn' seen on the scope then your power supply is bad, it may not be the Capacitor it can also be the IC's typically the LM723 and sometimes the LF301. If this is not the case then IC302 is probably bad and should be replaced.

 2) If the thump null looks funny (i.e. after getting the wave form as flat as Possible and you see peeks and valleys) replace both VCA's on the board.

 3) If you’re unable to achieve the gain setting of + 2dB then most likely the VCA Is bad. Replace all VCA's at this point.

 4) Typically I will also replace both VCA's on the other board. I try to use IC's from the same batch. This will save you many headaches down the line when you discover that the two channels will not balance out, or the levels between the two channels don't quite match right. (SAVE YOURSELF THE HASSLE CHANGES ALL VCAS IF ONE OF THEM SEEMS BAD!!!)

 Card #5
1) Note: there are two version of the #5 card. They current version is shown in the back of latest manual. The older #5 card with not work with the XT or XT2 chassis. Install RET-27 if a XT or XT2 chassis is to be used with the unit.

 2) Make sure R505 and R511 are 17.4k ohm resistors. The original ones were 16.2k ohms on older units. Also the R558 & 559 are 487k ohm resistors. The original ones were 17.4k ohm on older units.

 3) Replace power supply capacitors C512 and C513 if they are the orange ones with 100uF, 25V electrolytic.

 4) Check the proof / operate switch with a continuity tester. Make sure that it's not intermittent. The blue and black variety is very old, replace them when seen. Also replace switch it they seems stiff or hard to manipulate.

 5) Change the pots which are of the aluminum type.

 6) Clean the dirty pots with FREON TMS.

 7) The older modules are typically not mounted flush to the board, due to the Potting procedure used. While testing the card, try twisting the module back And forth if there is an intermittence between the solder pad and the module It will show up when the module of flexed. 

Card #6
1) Replace all orange capacitors, C632, C633, C626 & C627 with 100uf, 25V Electrolytic.

 2) Check the proof / operate switch with a continuity tester. Make sure that it's not intermittent. The blue and black variety is very old, replace them when seen. Also replace switch it they seems stiff or hard to manipulate.

 3) R633 and R667 should be 2.7k (old value 4.7k), R677 should be 14k (old Value 12k). Also optionally you may change R628 & R662 from 100k to 26.5k this change makes more accurate the yellow LED’s HF limiting indicators. With 100k The LED’s do not begin to flashes until about 8db gain reduction in the HF Limiter has already taken place.

 4) Turn R626, R660 and R6, 71 fully CW to defeat the FET bias and turn the Over shoot threshold to maximum before aligning.

 5) Older units which have the RET-27 installed should have the correct Modifications done see XT2 manual for more details.

 Card #8 & #9
1) Replace capacitors C827 & C828 if of orange type with 100uF, 25V Electrolytic.

 2) Replace capacitors C834 & C835 if of the orange type with 100uF, 63V Electrolytic.

 3) Verify diodes CR805 & CR806 are lifted if a # 0 card is installed.

 4) Verify jumpers are set correctly if a XT or XT2 chassis is installed. In older Units, R804 & R805 need to be lifted because there are no jumpers on the board.

 Card #7
1) Replace capacitors C724, C725, C712 & C713 if they are the orange type with 100uF, 25V electrolytic.

 2) Verify that IC701 & IC711 are LM318's.

 3) Verify that there is a 39pF capacitor soldered across R780.

 4) Verify that there is 220pF capacitor soldered across R747. This is an Optional modification installed on newer #7 cards to prevent high frequency Oscillation when the unit is initially powered up.

5) Verify that IC704 is AD518J. This is used in the original configuration of The #7 card and allows a maximum composite output level of no less that 4Vpp.

 6) On newer #7 cards use the MA332 IC, replaced R738 with a 100K pot and R739 with 10 ohms to achieve a maximum output of +12dBu.

 7) Note: Only on older PCB versions.
Install PCB modification at IC712 to prevent oscillations of the op-amp. Connect Pin 6 & 7 of IC712 together and Pin 5 to Ground trough a short piece of wire.

That's concludes the servicing.